A piston pump has been used for pumping liquids for many years. This design has become very widespread, as it works on the principle of displacing liquid by transmitting pressure. The operating principle of the piston pump of modern implementations is much more complex in comparison with the first models, due to which reliability and efficiency are significantly increased. Let us consider the features of such a mechanism in more detail.

Principle of operation

When considering the operating principle of a piston pump, it should be borne in mind that the first design appeared many decades ago. The work scheme has the following features:

1. The mechanism has a movable element that performs a reciprocating movement. It is produced by applying modern materials, due to which the insulating qualities are significantly increased.
2. The moving element is located in a cylindrical insulating container. When moving, the piston creates rarefied air in the working chamber, due to which liquid is sucked from the pipeline.
3. The reverse movement of the moving element leads to the squeezing of liquid into the outlet line. The valve design does not allow liquid to enter the suction line at the time of its ejection.

The simplest operating principle determines long-term and stable operation. It is worth considering that the flow created by such a device can move at different speeds. Too large a volume of the working chamber leads to the fact that the flow will move in jumps. In order to eliminate the occurrence of such an effect, a device with several pistons is installed.

Device

The plunger pump has a relatively simple design. Among the features we note the following points:

1. Working chamber. It is represented by a sealed case, which has a mirror surface in the inner part. Due to this, the movement of the moving element is significantly simplified. The working chamber is a part of the cylinder, which is determined by the maximum stroke of the rod. The surface of the cylinder is made using a material that is highly resistant to liquids.
2. The pressure and suction tubes are designed to drain and supply liquid. They can have different diameters. In addition, such a structural element may have a valve system, which significantly increases the efficiency of the mechanism.
3. The piston creates pressure in the system. The piston pump device has a piston, due to which the liquid is pumped. It is manufactured using several sealing materials. Due to this, the piston can move along the cylinder and at the same time create a vacuum. It is on the surface of the piston that serious pressure is exerted. Some versions are collapsible, allowing for repairs. For example, with prolonged use, seals wear out, which can be replaced if necessary to significantly extend the service life of the mechanism. However, there are also non-separable versions, the repair of which is possible only in special workshops.
4. The force is transmitted to the piston through the rod. In the manufacture of this element, high-quality steel with increased rigidity and strength is used. In addition, the materials used are characterized by high corrosion resistance, which significantly extends the service life of the structure. This element is connected to the drive through which force is transmitted. If the load is too high, the rod can become significantly deformed.

The reciprocating motion is transmitted from the electric motor through a special mechanism that converts the rotation. Modern options The designs are compact and can be installed for outdoor or indoor operation. In addition, in the manufacture of the case, metal is used that has high protection from environmental influences.

The device of the double-sided model has quite a large number of features:

1. There is a cylinder and a piston, as well as a rod. These elements are slightly different compared to those used to create a one-way mechanism.
2. Unlike the previous version, this one has two working chambers.
3. The two working chambers have their own discharge and suction valves.

Despite the significant increase in the efficiency of the piston pump, its design is quite simple. In this case, each stroke involves the suction and expulsion of liquid. This significantly increases the efficiency value.

Varieties

The most popular ones are on sale various options execution of piston pumps. Classification is carried out according to the following criteria:

1. The number of pistons that create pressure in the system.
2. The number of discharge and suction cycles in one stroke.

On sale there is a double-acting piston pump, as well as a version with one, three, or several pistons. As previously noted, by increasing the number of moving elements, the possibility of pulsating flow movement is eliminated. As for the number of cycles, there are single-acting and double-acting models, as well as differential models.

Classification can also be carried out according to the following criteria:

1. Power.
2. Throughput or performance.
3. Dimensions of the structure.
4. Layout features.

A variety of companies produce piston pumps. Quality may depend on the type of materials used, the popularity of the brand and the purpose of a particular model.

Areas of application

The liquid pump can be used to solve the most various tasks. The created design is characterized by high versatility. However, the presence of a moving element and the use of sealing rings when creating a piston makes it impossible to use a piston pump for pumping large volumes of liquids.

Considering the scope of application, we note the following points:

1. The materials used in manufacturing can withstand the effects of various chemical substances. That is why piston pumps are used to work with various types fuels, explosive mixtures and chemically aggressive environments.
2. There are quite a large number of models on sale that can be used for work at home.
3. IN Food Industry the design is also used extremely often. This is due to the delicate effect on the pumped medium.

In the manufacture of the structure, the most various materials, which determine the scope of application.

Advantages and disadvantages

A piston liquid pump is characterized by a fairly large number of advantages and disadvantages. The advantages include:

1. Simplicity of design. As previously noted, similar piston pumps were manufactured several decades ago and their design has changed insignificantly.
2. High reliability, which can be associated with the simplicity of the mechanism and the use of high-quality materials. Wear-resistant materials can withstand prolonged mechanical stress.
3. Ability to work with various media. The wide range of applications is determined by the fact that the materials used do not react to the effects of various chemicals.

There are also several serious drawbacks. An example is low productivity. Such models are less suitable for pumping large quantity liquids. In addition, the design is not suitable for long-term operation, since the active elements quickly wear out and lose their performance characteristics.

Piston pump

Piston pump (plunger pump) - one of the types of volumetric hydraulic machines in which the displacers are one or more pistons (plungers) performing reciprocating motion.

Rice. 2. Differential circuit for switching on a piston pump. During the movement of the piston to the left, part of the liquid is diverted into the rod cavity, the volume of which is less than the volume of the displaced liquid due to the fact that part of the volume of the rod cavity is occupied by the rod

Unlike many other positive displacement pumps, piston pumps are not reversible, that is, they cannot operate as hydraulic motors due to the valve distribution system.

Piston pumps should not be confused with rotary piston pumps, which include, for example, axial piston and radial piston pumps.

Principle of operation

The operating principle of a piston pump (Fig. 1) is as follows. When the piston moves to the right, a vacuum is created in the working chamber of the pump, the lower valve is open and the upper valve is closed, and liquid is sucked in. When moving in the opposite direction, excess pressure is created in the working chamber, and the upper valve is already open and the lower one is closed - liquid is pumped.

One type of piston pump is the diaphragm pump.

Fighting pulsation

One of the disadvantages of piston pumps, like other positive displacement pumps, is the pulsation of flow and pressure. Pulsations can be reduced by arranging several pistons in a row and connecting them to one shaft so that their operating cycles are shifted in phase relative to each other at equal angles. Another way to combat pulsation is to use a differential pump activation circuit (Fig. 2), in which liquid is pumped not only during the forward stroke of the piston, but also during the reverse stroke.

Double-acting pumps are also widely used, in which both the piston and rod chambers have (in contrast to the differential switching circuit) their own valve distribution system. Such pumps have a lower pulsation coefficient and higher efficiency than single-acting pumps (Fig. 1).

To combat pulsation, hydraulic accumulators are also used, which at the moment highest pressure They store energy and release it when the pressure drops.

Application

Piston pumps have been used since ancient times. Their use for water supply purposes has been known since the 2nd century BC. Currently, piston pumps are used in water supply systems, in the food and chemical industries, and in everyday life. Diaphragm pumps are used, for example, in fuel supply systems in internal combustion engines.

see also

Literature

1. Hydraulics, hydraulic machines and hydraulic drives: Textbook for mechanical engineering universities / T. M. Bashta, S. S. Rudnev, B. B. Nekrasov and others - 2nd ed., revised. - M.: Mechanical Engineering, 1982.
2. Geyer V. G., Dulin V. S., Zarya A. N. Hydraulics and hydraulic drive: Textbook for universities. - 3rd ed., revised. and additional - M.: Nedra, 1991.

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See what a “piston pump” is in other dictionaries:

piston pump- A reciprocating pump, the working parts of which are made in the form of pistons. [GOST 17398 72] Subjects pump EN piston pump DE Kolbenpumpe FR pompe à pistons ...

A positive-displacement pump whose working body is a piston that performs a reciprocating movement in a cylinder... Big Encyclopedic Dictionary

A positive-displacement pump whose working body is a piston that performs a reciprocating movement in a cylinder. * * * PISTON PUMP PISTON PUMP, a volumetric pump, the working element of which is a piston that performs a reciprocating movement in ... ... encyclopedic Dictionary

piston pump- stūmoklinis siurblys statusas T sritis automatika atitikmenys: engl. piston pump; positive displacement pump vok. Kolbenpumpe, f; Pumpe in Verdrängungsbauart, f; volummetrische Pumpe, f rus. piston pump, m pranc. pompe à piston, f; pompe… … Automatikos terminų žodynas

piston pump- stūmoklinis siurblys statusas T sritis fizika atitikmenys: engl. piston pump vok. Kolbenpumpe, f rus. piston pump, m pranc. pompe à piston, f … Fizikos terminų žodynas

piston pump- stūmoklinis siurblys statusas T sritis Energetika apibrėžtis Slankiojamojo judesio siurblys, kurio pagrindinis darbinis mechanizmas yra stūmoklis. Skysčio tiekimo netolygumui sumažinti naudojami daugiacilindriai siurbliai arba pneumatiniai ar… … Aiškinamasis šiluminės ir branduolinės technikos terminų žodynas

See Art. Pump... Great Soviet Encyclopedia

A reciprocating pump, the working parts of which are made in the form of pistons (see figure). The unevenness of fluid supply is reduced by using multi-cylinder P. n., as well as pneumohydraulic. batteries. Head 10,000 m or more. They find... ... Big Encyclopedic Polytechnic Dictionary

piston pump- volumetric pump... Dictionary of Russian synonyms for automatic control technologies

axial piston pump- A rotary piston pump, in which the axis of rotation of the rotor is parallel to the axes of the working elements or makes an angle with them less than or equal to 45°. [GOST 17398 72] Subjects pump EN axial piston pump DE Axialkolbenpumpe FR pompe à pistons axiaux … Technical Translator's Guide

Piston pumps are among the volumetric pumps in which the movement of liquid is carried out by displacing it from fixed working chambers by displacers. Working chamber positive displacement pump is a limited space that alternately communicates with the inlet and outlet of the pump. Displacer is called the working body of the pump, which displaces liquid from the working chambers (plunger, piston, diaphragm).

Piston pumps are classified according to the following indicators: 1) by type of displacer: plunger, piston and diaphragm; 2) by the nature of the movement of the leading link: reciprocating movement of the leading link; rotational movement of the drive link (crank and cam pumps); 3) by the number of discharge and suction cycles in one double stroke: single-acting; double acting. 4) by the number of pistons: single-piston; two-piston; multi-piston.

Rice. 7.3. Single acting piston pump

Single action pump . The diagram of a single-action pump is shown in Fig. 7.3. Piston 2 connected to the crank mechanism through a rod 3 , as a result of which it performs a reciprocating motion in the cylinder 1 . When the piston moves to the right, it creates a vacuum in the working chamber, causing the suction valve 6 liquid also rises from the supply tank 4 through the suction pipeline 5 enters the working chamber 7 . When the piston moves in reverse (to the left), the suction valve closes and the discharge valve 8 opens and liquid is forced into the pressure pipe 9 .

Since each engine revolution corresponds to two piston strokes, of which only one corresponds to discharge, the theoretical productivity per second will be

Where F- piston area, m²; l- piston stroke, m; n- engine speed, rpm.

To increase the performance of piston pumps, they are often made in double, triple, etc. The pistons of such pumps are driven by a single crankshaft with offset cranks.

Actual pump performance Q less than theoretical, since leaks occur due to untimely closing of valves, leaks in valves and piston and rod seals, as well as incomplete filling of the working chamber.

Valid Feed Ratio Q to theoretical Q T is called the volumetric efficiency of a piston pump:

Volumetric efficiency is the main economic indicator characterizing the operation of the pump.

Rice. 7.4. Double acting piston pump

Double acting pump . A more uniform and increased supply of liquid, compared to a single-action pump, can be achieved with a double-action pump (Fig. 7.4), in which each piston stroke corresponds to simultaneous suction and discharge processes. These pumps are made horizontal and vertical, the latter being the most compact. The theoretical capacity of a double acting pump will be

Where f- rod area, m2.

Rice. 7.5. Diagram of a piston pump with a differential piston

Differential pump . In a differential pump (Fig. 7.5) the piston 4 moves in a smoothly machined cylinder 5 . The piston is sealed by an oil seal 3 (option I) or small gap (option II) with the cylinder wall. The pump has two valves: suction 7 and injection 6 , as well as an auxiliary camera 1 . Suction occurs in one stroke of the piston, and discharge in both strokes. So, when the piston moves to the left from the auxiliary chamber into the discharge pipeline 2 a volume of liquid is displaced equal to (F - f)l; When the piston moves to the right, a volume of liquid equal to f l. Thus, during both strokes of the piston, a volume of liquid equal to

(F - f)l + fl = Fl

those. the same amount as supplied by a single-action pump. The only difference is that this amount of liquid is supplied during both strokes of the piston, therefore, the supply occurs more evenly.

According to GOST 17398, pumps according to the principle of operation and design are divided into two main groups - dynamic and volumetric (table).

Dynamic pumps include pumps in which the liquid in the chamber moves under force and has a constant connection with the inlet and outlet pipes. This force action is carried out using an impeller, which imparts kinetic energy to the fluid, which is transformed into pressure energy. Dynamic pumps are vane, electromagnetic, friction and inertia pumps.

Volumetric pumps include pumps in which the energy of the fluid is transferred according to the principle of mechanical periodic displacement of the fluid by a working fluid, which creates a certain fluid pressure during the movement. In positive displacement pumps, the liquid receives energy as a result of periodic changes in a closed volume, which alternately communicates with the input and output of the pump. Displacement pumps include piston, plunger, diaphragm, rotary and gear pumps.

Vane pumps are pumps in which energy is transferred using a rotating blade wheel (which serves as their working body), through the dynamic interaction of the wheel blades with the liquid flowing around them. Vane pumps are centrifugal, axial and diagonal.

Centrifugal pumps are called vane pumps with fluid movement through the impeller from the center to the periphery, axial - vane pumps (GOST 9366) with fluid movement through the impeller in the direction of its axis. The impellers of axial pumps consist of several screw cavities shaped like propeller blades.

Friction and inertia pumps are a group of dynamic pumps in which energy is transferred to a fluid by friction and inertia forces. These include vortex, screw, labyrinth, worm and jet pumps. Vane pumps are also classified according to pressure, power and speed coefficient.

By pressure(m head of liquid) pumps are distinguished: Low-pressure up to 20 m, medium-pressure from 20 to 60, high-pressure over 60.

By power(kW) pumps can be micropumps up to 0.4, small up to 4, small up to 100 with a flow rate of 0.5 m 3 /s, medium up to 400, large over 400 with a flow rate above 0.5 m 3 /s, unique over 8000 when feeding over 20 m 3 /s.

Speed ​​coefficient

,

where n is the rotation speed, rpm; Q - flow, m 3 /s; H- head, m.

In this formula, the pressure H for multistage pumps is understood as the pressure developed by one wheel (stage). If the pump has a double-entry impeller, substitute a Q value equal to half the flow. The speed coefficient represents the most complete hydraulic characteristic centrifugal pumps, allows you to classify pumps not according to one particular parameter (flow rate, pressure or rotation speed), but according to their combination and provides a basis for comparing different types of pumps and choosing the pump most suitable for operation under given conditions. For different types of vane pumps, the ns rpm values ​​are given below:

Centrifugal ones are low-speed 50...80, normal 80...150, high-speed 350...500. Diagonal pumps have a coefficient speed is in the range of 350...500, and for axial ones 500...1500.

The speed factor ns also determines the shape of the pump impeller. As an example, consider the wheels of pumps of different speeds. A low-speed wheel is characterized by the fact that the output diameter is much larger than the input diameter and the wheel has a relatively small width. With increasing speed, this difference decreases, the width increases, and then the wheel becomes diagonal and axial.

Classification of pumps by design and purpose.

When classifying vane pumps by design, the following characteristics are taken into account: the location of the axis of rotation (vertical, horizontal), the location and design of the supports (cantilever, with external or internal supports, etc.), the number of wheels (one-, two- and multi-stage), implementation of inlet and outlet (with a semi-spiral or chamber inlet, with a blade outlet, etc.), the presence of regulation, the design of the housing (with a longitudinal connector, sectional, etc.), immersion under the level, type of seal (with a soft seal, with a mechanical seal, etc.), design of the impeller (with an open or closed impeller, rotary-vane, with two-way entry, etc.), self-priming ability, tightness, the presence of a structural connection with the engine, heating systems or cooling, pre-connected screw, purpose (for installation in a well, capsule, etc.).

When classified by purpose, pumps are distinguished: general purpose (table) for pumping clean water with a small content of suspended particles; for pumping pulp or soil - dredgers, soil and mud; for supplying water from wells - electric submersible with a motor located under the water level, and deep, in which the motor is installed above the well, and the pump is located in the well under water (a sectional shaft goes from the pump to the motor, held in guide bearings installed in crosspieces between sections of water-lifting pipes); for pumping gasoline, kerosene or oils, chemicals, etc.

Type K and KM pumps are single-stage cantilever pumps with a liquid inlet into the impeller on one side. They have the following characteristics: head 8.8...9.8 m, suction height up to 8 m and flow 4.5...360 m/h.

Depending on the size, each pump has its own brand, which indicates the diameter of the inlet pipe, the speed coefficient and the type of pump. Thus, the number 8 on a cantilever pump of the 8K-18 brand means the diameter of the inlet pipe (mm), reduced by 25 times, the cantilever type of pump is designated by the letter K, and the number 18 means the speed coefficient of the pump reduced by 10 times.

ND type pumps are single-wheel horizontal pumps with a two-way supply of liquid to the impeller. There are three types of such pumps: NDn (low pressure), NDs (medium pressure) and NDv (high pressure). Each of the three varieties has several sizes. The diameter of the pressure pipe (mm), reduced (rounded) by 25 times, is indicated by a number before the letters in the pump brand. The suction height of such pumps does not exceed 7 m.

Pumps of the NDn type have a flow of 1350...5000 m3 / h and a head of 10 to 32 m;

pumps type NDs - flow 216...6500 m3/h and head 18...90 m,

NDv type pumps deliver from 90 to 720 m3/h and pressure 22...104 m.

Pumps of the NMK, TsNS, TsNNM, TsK types are multi-stage horizontal pumps, where the liquid is supplied from both sides to the first impeller. These pumps have several varieties with the number of wheels from 2 to 11. They have a head of up to 2000 m and a flow of 3600 m3/h.

The group of horizontal centrifugal pumps includes single-wheel pumps of type D with a flow of 380...12,500 m3/h and a head of 12...137 m, four-stage pumps of type M with a flow of 700...1200 m3/h and a head of 240... 350 m three- and five-stage pumps type MD with a flow of 90...320 m/h and a head of 138...725 m four- and six-stage sectional pumps of the NGM type with a flow of 54...90 m/h and a head of 102.. .210 m.

Let's consider vertical centrifugal and axial pumps for pumping water and clean liquids.

Pumps of the NDsV type - they are produced in two standard sizes: 207 DV and 24 NDv. These are single-stage vertical medium-pressure pumps with two-way liquid inlet into the impeller. The flow is 2700...6500 m3/h, the pressure is 40...79 m.

Type B pumps are the largest pumps, single-stage vertical with one-way liquid entry into the impeller. They are produced with a flow from 3000 to 6500 m3/h, a head of 18...72 m in several standard sizes.

Axial pumps. Vane pumps in which the fluid moves through the impeller parallel to its axis are called axial pumps.

Such pumps are designed to supply large quantities of liquid at relatively low pressures. In axial pumps, the fluid flow emerging from the channels of the impeller has a vortex structure with a twist, and when it enters the stationary channels of the straightening apparatus, it unwinds, gradually moving in the axial direction.

Advantages of axial pumps: simplicity and compact design. Compact design is crucial for large flow rates and, therefore, for large pipeline diameters. Axial pumps can be installed on a vertical, horizontal or inclined pipe.

In axial pumps, the liquid, moving translationally, simultaneously receives rotational motion created by the impeller. To eliminate the rotational movement of the liquid, a guide device is used, through which the liquid flows before exiting into the pressure pipeline.

Diagonal pumps. The design of diagonal pumps is similar to axial pumps; their main difference is the shape of the impeller. The liquid medium moves in the impeller at an angle to the pump axis (diagonally), which determines the name of these pumps.

A diagonal pump of a rotary vane type with an impeller with a diameter of 2 m (Fig.) is designed for a head of 30 m. The blades of the impellers can be rigidly mounted and can be rotary, i.e. their installation is adjustable.

Liquid ring pumps belong to the group of self-priming or vacuum pumps.

Their design is such that they can suck in both air and water. A big drawback of centrifugal pumps of conventional designs is their inability to independently absorb liquid, since the air initially located in the suction pipe, due to its low mass, cannot be pumped out to create a sufficiently deep vacuum to ensure the rise of liquid until it fills the pump impeller. Liquid ring pumps can create significant vacuum in the air, and therefore lift liquid through the suction pipe to a sufficiently high height, i.e. they can suck in liquid themselves without first priming the pump. This phenomenon is called self-suction.

Liquid ring pumps are used as independent units for pumping gases or liquids, but more often as auxiliary units to ensure the filling of large centrifugal pumps, as well as to create and maintain a vacuum in various containers and apparatus.

The pressure of a vortex pump is 4...6 times greater than that of a centrifugal pump, with the same dimensions and rotation speed. Vortex pumps are produced in single-stage and two-stage versions. In addition, vortex pumps have self-priming ability, which allows them to be used as vacuum pumps when priming large centrifugal pumps. Vortex pumps have a relatively low efficiency (25...55%). They produce combined pumps, in which both vortex and centrifugal impellers are placed in one housing.

A comparison of the technical data of vortex and centrifugal-vortex pumps shows that with the same flow rates, vortex and centrifugal-vortex pumps operate at higher pressures, but relatively low efficiencies.

Airlifts ( emulsion water lifts). Airlifts are used in sewers to lift household fecal and waste industrial wastewater.

Typically, an airlift is a lifting pipe designed to raise a mixture of water and air. The pipe is lowered into a well, to which compressed air is supplied through another pipe. Both pipes are inserted into casing pipe wells and lowered to water level.

The operating principle of the airlift is as follows. When immersed in water, the riser pipe fills with water. Air and water supplied into the pipe form a water-air mixture, which has a lower density compared to water and, therefore, rises to a higher level. In this way, water is transported from the well to the water-air reservoir. Here the water is freed from air and flows by gravity to the consumer.

In the case of temporary use of air-lift installations (for example, during construction during water depletion or during surveys when performing test pumping), it is possible to do without water-lifting pipes. In this case, the air supplied through the water-lifting pipe 4 is released directly into the casing pipe, where it mixes with water. The resulting water-air emulsion will flow directly through the casing.

Advantages of airlifts: absence of rubbing and blocking parts in the well, the ability to pass contaminated water and use curved wells, simplicity of design, etc.

The main disadvantages: low efficiency of the airlift installation (10... 15%), the need for a second rise of water from the collection tank to the consumer using a centrifugal or other pump, and the need for significant (at least 50% of the total height) immersion of the airlift nozzle under the dynamic water horizon ( DHA) formed during airlift operation.

Question No. 36. Dynamic pump pressure.

The dynamic pressure of a pump is the increment in the kinetic energy of a unit mass of liquid in the pump.

This is the portion of the total head that relates to the velocity of the fluid. The dynamic head Hd is determined by the following formula: Hd = v/2g where: V is the fluid velocity measured at the inlet (in m/s); g – free fall acceleration (in m/s?). If the inlet and outlet pipes have different diameters, the dynamic pressure is the difference in the dynamic pressures at the suction and outlet. If the inlet and outlet pipes have the same diameter, then there is no dynamic pressure.

Question No. 37. Performance, power and efficiency of a dynamic pump.

Productivity (Q) is usually expressed in cubic meters x per hour (m 3 / hour). Since fluids are completely incompressible, there is a direct relationship between performance, or flow rate, pipe size and fluid velocity. This relationship has the form: Where ID is the internal diameter of the pipeline, inch V is the fluid speed, m/sec Q is the productivity, (m 3 /hour)

Rice. 1. Suction head - shows the geometric heads in the pumping system, where the pump is located above the suction reservoir (static head)

Power and efficiency The work performed by a pump is a function of the total head and the weight of the fluid pumped over a given period of time. As a rule, the formulas use the pump performance parameter (m 3 / hour) and liquid density instead of weight. The power consumed by the pump (bhp) is the actual power on the pump shaft imparted to it by the electric motor. Pump output power or hydraulic (whp) is the power supplied by the pump to the liquid medium. These two definitions are expressed by the following formulas. The pump input power (power input) is greater than the pump output power or hydraulic power due to mechanical and hydraulic losses occurring in the pump. Therefore, pump efficiency (Pump Efficiency) is defined as the ratio of these two values. Speed ​​and pump type Speed ​​is a calculation factor used to classify pump impellers by type and size. It is defined as the speed of rotation of a geometrically similar impeller delivering 0.075 m 3 /s of fluid at 1 m of head. (U.S. units of 1 gpm at 1 ft of head) However, this definition is used for engineering design purposes only, and speed must be understood as a coefficient for calculating certain pump characteristics. To determine the speed coefficient, the following formula is used: Where N – Pump speed (in revolutions per minute) Q – Capacity (m 3 /min) at the point of maximum efficiency. H – Pressure at the point of maximum efficiency. Speed ​​determines the geometry or class of the impeller, as shown in Fig. 3
Rice. 3 Wheel shape and speed As speed increases, the ratio between the outer diameter of the impeller D2 and the inlet diameter D1 decreases. This ratio is 1.0 for an axial flow impeller. Impellers with radial blades (low Ns) generate pressure due to centrifugal force. Pumps with higher Ns generate pressure partly using the same centrifugal force and partly using axial forces. The higher the speed coefficient, the greater the share of axial forces in creating pressure. Axial flow or propeller pumps with a speed factor of 10,000 (in US units) and higher generate pressure solely due to axial forces. Radial flow impellers are typically used when high heads and low flow rates are required, while axial flow impellers are used for high-volume, low-capacity applications. Positive Positive Head (NPSH), Inlet Pressure and Cavitation The Hydraulic Institute defines the NPSH parameter as the difference between the absolute pressure of the liquid at the inlet of the impeller and the saturated vapor pressure. In other words, this is the excess of the internal energy of the liquid at the entrance to the impeller by its saturated vapor pressure. This ratio allows you to determine whether the liquid in the pump will boil at the point of minimum pressure. The pressure that a liquid exerts on the surfaces surrounding it depends on the temperature. This pressure is called vapor pressure, and it is a unique characteristic of any liquid that increases with temperature. When the vapor pressure of a liquid reaches ambient pressure, the liquid begins to evaporate or boil. The temperature at which this evaporation occurs will decrease as the ambient pressure decreases. When a liquid evaporates, it increases in volume significantly. One cubic meter of water at room temperature turns into 1700 cubic meters of steam (evaporation) at the same temperature. From the above it is clear that if we want to pump liquid effectively, we need to keep it in a liquid state. Thus, NPSH is defined as the value of the actual suction height of the pump at which evaporation of the pumped liquid will not occur at the point of minimum possible liquid pressure in the pump. Required NPSH value (NPSHR) - Depends on pump design. As fluid passes through the pump suction port and enters the impeller guide vane, fluid velocity increases and pressure drops. Pressure losses also occur due to turbulence and uneven fluid flow, because the liquid hits the wheel. The centrifugal force of the impeller blades also increases the speed and reduces the pressure of the fluid. NPSHR is the required head pressure at the pump suction port to compensate for all pressure losses in the pump and keep the liquid above the vapor pressure level and limit the head losses resulting from cavitation to 3%. A three percent head drop margin is a generally accepted NPSHR criterion adopted to facilitate calculations. Most low suction pumps can operate at low or minimal NPSHR without seriously affecting their life. NPSHR depends on the speed and performance of the pumps. Pump manufacturers typically provide NPSHR information. Allowable NPSH (NPSHA) is a characteristic of the system in which the pump operates. This is the difference between atmospheric pressure, pump suction lift and saturated vapor pressure. The figure shows 4 types of systems, for each there are formulas for calculating the NPSHA system. It is also very important to take into account the density of the liquid and bring all quantities to one unit of measurement.
Rice. 4 Calculation of the liquid column above the pump suction pipe for typical suction conditions Pv - Atmosphere pressure , in meters; Vр - Pressure of saturated vapors of a liquid at the maximum operating temperature of the liquid; P - Pressure on the surface of the liquid in a closed container, in meters; Ls - Maximum suction lift, in meters; Lн - Maximum height of support, in meters; Hf - Friction loss in the suction pipeline at the required pump performance, in meters. In a real system, NPSHA is determined using a pressure gauge mounted on the suction side of the pump. The following formula is used: Where Gr - Pump suction pressure gauge readings, expressed in meters, taken with a plus (+) if the pressure is above atmospheric and with a minus (-) if below, adjusted for the centerline of the pump; hv = Dynamic pressure in the suction pipe, expressed in meters. Cavitation is a term used to describe the phenomenon that occurs in a pump when the NPSHA is insufficient. In this case, the liquid pressure is lower than the saturated vapor pressure, and the smallest vapor bubbles of the liquid move along the impeller blades; in the high-pressure area, the bubbles quickly collapse. The destruction or “explosion” is so rapid that it can be heard as a rumbling sound, as if gravel had been poured into a pump. In high suction pumps, the bubble explosions are so strong that the impeller blades are destroyed within just a few minutes. This effect can increase and under certain conditions (very high suction capacity) can lead to serious erosion of the impeller. Cavitation that has arisen in the pump is very easy to recognize by its characteristic noise. In addition to damage to the impeller, cavitation can lead to a decrease in pump performance due to the evaporation of liquid occurring in the pump. When cavitation occurs, the pump head may decrease and/or become unstable, and the pump's power consumption may also become unstable. Vibrations and mechanical damage such as bearing damage can also result from running a pump with high or very high suction capacity due to cavitation. To prevent the unwanted effect of cavitation for standard low suction pumps, it is necessary to ensure that the system NPSHA is higher than the pump NPSHR. High suction pumps require reserve for NPSHR. The Hydraulic Institute standard (ANSI/HI 9.6.1) suggests an increase in NPSHR of 1.2 to 2.5 times for high and very high suction pumps when operating within the acceptable performance range.

Question No. 38. Basic equation for the operation of centrifugal pumps.

The basic equation of a centrifugal pump is for the first time general view was obtained in 1754 by L. Euler and bears her name.

Considering the movement of liquid inside the impeller, we will make the following assumptions: the pump pumps ideal liquid in the form of jets, i.e., there are no types of energy losses in the pump. The number of identical pump blades is infinitely large (z = µ), their thickness is zero (d = 0), and the angular speed of rotation of the wheel is constant (w = const.).

Liquid is supplied axially to the impeller of a centrifugal pump at a speed Vo, i.e. in the direction of the shaft axis. Then the direction of the liquid jets changes from axial to radial, perpendicular to the shaft axis, and the speed due to centrifugal force increases from the value V1 in the space between the blades of the impeller to the value V2 at the exit of the wheel.

In the inter-blade space of the impeller, when the fluid moves, absolute and relative flow velocities are distinguished. Relative speed flow - speed relative to the impeller, and absolute - relative to the pump housing.

Rice. Diagram of fluid movement in the impeller of a centrifugal pump

The absolute speed is equal to the geometric sum of the relative fluid speed and the peripheral speed of the impeller. The peripheral speed of the fluid exiting between the impeller blades coincides with the peripheral speed of the wheel at a given point.

Peripheral fluid velocity (m/s) at the impeller inlet

Peripheral speed of liquid at the outlet of the impeller (m/s)

Where n-impeller rotation speed, rpm; D1 And D2 - internal and external diameters of the impeller, m, w- angular speed of rotation of the impeller rad/s

When the impeller moves, fluid particles move along the blades. Rotating together with the impeller, they acquire a peripheral speed, and moving along the blades - a relative speed.

The absolute speed v of the fluid movement is equal to the geometric sum of its components: the relative speed w and district u, i.e. v = w+ And.

The relationship between the velocities of liquid particles is expressed by a parallelogram or triangles of velocities, which makes it possible to give an idea of ​​the radial and circumferential components of absolute velocity.

Radial component

circumferential component

where a is the angle between the absolute and peripheral speeds (at the impeller inlet a1 and at the outlet a2).

The angle b between the relative and peripheral speeds characterizes the outline of the pump blades.

We study the change in 1 since the moment of momentum of the mass of the liquid t = rQ, Where r- liquid density; Q- pump supply.

Using the theorem of mechanics on the change in angular momentum in relation to the movement of liquid in the channel of the impeller, we will derive the basic equation of a centrifugal pump, which will allow us to determine the pressure (or pressure) developed by the pump. This theorem states: the change in time of the main angular momentum of a system of material points relative to a certain axis is equal to the sum of the moments of all forces acting on this system.

The moment of momentum of the fluid relative to the axis of the impeller in the inlet section

Moment of momentum at the impeller exit

where r1 and r2 - distances from the wheel axis to the input V1 and output V2 speed vectors, respectively.

According to the definition of the moment of the system, we can write:

Since according to Fig.

Groups of external forces - gravity, pressure forces in the design sections (inlet-outlet) and on the side of the impeller and fluid friction forces on the streamlined surfaces of the impeller blades - act on the mass of liquid filling the inter-blade channels of the impeller.

The moment of gravity forces relative to the axis of rotation is always equal to zero, since the leverage of these forces is equal to zero. For the same reason, the moment of pressure forces in the design sections is also equal to zero. If the friction forces are neglected, then the moment of the friction forces is zero. Then the moment of all external forces relative to the axis of rotation of the wheel is reduced to the moment Mk the dynamic effect of the impeller on the fluid flowing through it, i.e.

Work Mk by relative speed is equal to the product of flow rate and theoretical pressure P.T. created by the pump, i.e. equal to the power transmitted to the fluid by the impeller. Hence,

This equation can be represented as

Dividing both parts into Q, we get

Considering that pressure N = Р/(pg) and substituting this value we get

If we neglect friction forces, we can obtain dependencies called basic equations of a vane pump. These equations reflect the dependence of the theoretical pressure or head on the main parameters of the impeller. The transfer speeds at the entrance to the axial pump and at the exit from it are the same, so the equation takes the form

In most pumps, liquid enters the impeller almost radially and, therefore, the speed V1 » 0. Taking into account the above

or

The theoretical pressure and pressure developed by the pump, the greater, the greater the peripheral speed on the outer circumference of the impeller, i.e., the larger its diameter, rotation speed and angle b2, i.e., the “steeper” the impeller blades are located.

The actual pressure and pressure developed by the pump are less than the theoretical ones, since the actual operating conditions of the pump differ from the ideal ones accepted when deriving the equation. The pressure developed by the pump decreases mainly due to the fact that with a finite number of impeller blades, not all fluid particles are deflected uniformly, as a result of which the absolute speed decreases. In addition, part of the energy is spent on overcoming hydraulic resistance. The influence of the finite number of blades is taken into account by introducing a correction factor k(characterizing a decrease in the circumferential velocity component V2u), a decrease in pressure due to hydraulic losses - by introducing a hydraulic efficiency hr. Taking these corrections into account, the total pressure

and full pressure

Coefficient value hr depends on the design of the pump, its dimensions and the quality of the internal surfaces of the wheel flow part. Usually the value hr is 0.8...0.95. Meaning k with the number of blades from 6 to 10, a2 = 8...14 0 and V2u = 1.5...4 m/s, it ranges from 0.75 to 0.9.

When the impeller of a centrifugal pump rotates, the liquid located between the blades, thanks to the developed centrifugal force, is thrown through the volute chamber into the pressure pipeline. The escaping liquid frees up the space it occupies in the channels on the inner circumference of the impeller, so a vacuum is formed at the entrance to the impeller, and excess pressure is formed at the periphery. Under the influence of the difference in atmospheric pressure in the receiving tank and the reduced pressure at the inlet to the impeller, the liquid flows through the suction water supply into the inter-blade channels of the impeller.

A centrifugal pump can only operate if its internal cavity is filled with the pumped liquid not lower than the pump axis, therefore the pumping unit is equipped with a device for priming the pump.

Question No. 39. Performance characteristics of the N-0 centrifugal pump.

The characteristic of a centrifugal pump, or external and operating characteristics, is the graphical dependence of the main indicators of the pump, such as pressure, power and efficiency, on flow, and the cavitation characteristic is a graph of the dependence of pressure, flow and efficiency on excess suction pressure N.

All pump parameters are interconnected, and changing one of them inevitably entails changing the others. If, at a constant rotor speed, the pump flow is increased, the pressure it creates will decrease. When operating conditions change, the efficiency of the pump also changes: at certain certain values ​​of flow and pressure, the efficiency of the pump will be maximum, and under all other modes of its operation, the pump operates with worse efficiency. Note that the efficiency is greatly influenced by the speed coefficient .

The characteristics of centrifugal pumps clearly show the efficiency of their operation in various modes and allow you to accurately select the most economical pump for given operating conditions.

Due to hydraulic losses and variability of hydraulic efficiency, the operating characteristic of the pump differs from the theoretical one.

Pressure losses in the impeller consist of losses due to friction in the channels of the impeller, losses due to impact when the speed at the entrance to the impeller deviates from the tangential direction in the blade, etc.

As can be seen from Fig. b, all dependencies are plotted on one graph on the appropriate scales, and the flow Q pump is plotted along the abscissa axis, and pressure H, vacuum height, power and efficiency are plotted along the ordinate axis.

To determine the required pump parameters from the operating characteristics, proceed as follows. According to a given pump flow Qo found on the curve Q -N point C, from which a horizontal line is drawn until it intersects with the scale N, where the pressure corresponding to the given flow rate is found. To determine the power and efficiency of the pump, draw horizontal straight lines from the points A And IN and on scales N and h and thus find the corresponding values No and ho.

Pump performance has several distinct points and areas. The starting point of the characteristic corresponds to zero pump flow Q=0, which is observed when the pump operates with a closed valve on the pressure pipeline. As can be seen from Fig. and, in this case, the centrifugal pump develops a certain pressure and consumes power, which is spent on mechanical losses and heating the water in the pump.

The operating mode of the pump corresponding to maximum efficiency is called optimal. The main goal of selecting pumps is to ensure their operation at optimal conditions, taking into account that the efficiency curve is flat in the zone of the optimal point, however, in practice, they use the working part of the pump characteristics (a zone corresponding to approximately 0.9hmax, within which the selection and operation of pumps is allowed ).

Cavitation characteristics necessary to assess the cavitation properties of pumps and the right choice suction height. To build the cavitation characteristics of the pump, it is subjected to cavitation tests on special stands.

Within certain limits of change in excess suction pressure Hvs.iz values Q, N And h remain unchanged. At certain values ​​of Hvs.izb, noise and crackling noises appear during pump operation, characterizing the onset of local cavitation. With a further decrease in Hvs.iz value Q, N And h begin to gradually decrease, cavitation noise increases and ultimately the pump fails. Determine precisely the moment when cavitation begins to affect Q, N And h is not possible, therefore, the minimum excess suction height Hvs.iz min is conventionally taken as its value at which the pump flow drops by 1% of its original value.

Very often, the Nvac curve is also applied to the performance characteristics of pumps - Q, which gives the values ​​of the permissible vacuum suction height depending on pump supply.

Question No. 40. Velocity triangles. Recalculation and modeling of parameters.

Fig.2.1. Fluid movement in the impeller

In the interblade channels of the impeller, fluid particles participate in a complex movement:

 portable - together with the impeller;

 relative - in relation to the walls of the interscapular canals;

 absolute - resulting in relation to the above movements.

The absolute velocity vector of a particle can be represented by the sum of the portable (peripheral) velocity and the relative velocity.

The relative velocity of the particle at any point in the blade profile is tangential to it. Absolute speed is decomposed into circumferential speed V iu and meridian (consumable) V i m components that are determined by the following formulas

Where i= 1.2. The index "1" corresponds to the parameters of the fluid at the entrance to the impeller, and "2" - at the exit from it.

2.1. Basic Equation of Turbomachinery

(Eulerian turbine equation)

The basic equation of turbomachines connects the geometric and kinematic characteristics of the impeller with the pressure it develops. When deriving it, it is assumed that the trajectory of liquid particles in the interblade channels repeats the outline of the blade profile, i.e. for the impeller, the assumption is made that the number of infinitely thin blades located on it is infinite (a sign of this will be the symbol  as an index).

The conclusion is based on the equation of angular momentum for steady motion of fluid in uniformly rotating channels, according to which the change per unit time of angular momentum of the fluid L located in the channel is equal to the moment of external forces acting on it:

External forces acting on the liquid in the channel include the forces with which the channel walls act on the liquid, pressure forces, friction forces, and gravity. The analysis shows that the resultant pressure forces on the inner and outer generatrices of the wheel pass through the axis of rotation and do not create torque. Due to the symmetry of the impeller, the forces of gravity are balanced, and the frictional forces acting on the peripheral surfaces of rotation are small. Based on the above, it is assumed that the moment is created only by forces arising from the interaction of the walls of the working channels with the liquid located in them.

This moment of external forces is related to the hydraulic power of the pump N g and angular rotation speed  with the following ratio:

Substituting the found values ​​into the law of change in angular momentum over time, we obtain the Euler equation:

. (2.1)

Euler's equation connects the theoretical pump head with fluid speeds, which depend on the pump flow, the angular speed of rotation of the impeller, as well as its geometric characteristics.

The flow at the entrance to the impeller is created by the device preceding it (supply). Therefore, the moment of speed (spin) is determined by the design of the inlet. The supply devices of many pumps do not spin the flow and the inlet torque is zero. In this case, the theoretical pressure is determined by the following equation:

where is the peripheral speed at the periphery of the wheel.

Considering that

Where n- rotation speed, rpm;

and the projection of the absolute speed at the exit from the wheel onto the peripheral speed, as follows from the speed triangle (see Fig. 2.1), is determined by the expression

the equation for the theoretical pressure will take the form:

This equation shows that the pressure depends on the value of the meridian component of the absolute speed at the outlet of the wheel, which is related to the pump flow by the equation

Where b 2 - width of the impeller channel at the outlet.

Theoretical head with a finite number of blades H t is less, which is taken into account by introducing a correction factor into the Euler equation 

From the consideration of velocity triangles (Fig. 2.1), based on the cosine theorem, we can write

Taking into account the given dependencies, the Euler equation can be transformed to the form:

where is the pressure created due to the action of centrifugal forces in the flow;

Pressure created by changing the relative speed in the impeller channel;

The pressure created by changing the absolute speed in the impeller channel.

The quantity is called the static part of the pressure, and the dynamic part of the pressure.

In order to reduce losses in the pump, it is desirable that the static part of the pressure predominates, due to the centrifugal component.

Question No. 41. Operation of a centrifugal pump on a given pipeline.

The combination of a pump, receiving and pressure tanks, pipelines connecting the above elements, control and shut-off valves, as well as control and measuring equipment constitutes a pumping unit. To move liquid through pipelines from the receiving tank to the pressure tank, it is necessary to expend energy on:

 rise of liquid to a height H g, equal to the difference in levels in the tanks (this value is called geometric pressure pumping unit);

 overcoming the pressure difference in them p n and p n;

 overcoming total hydraulic losses  h n in the suction and pressure pipelines.

Thus, the energy required to move a unit weight of liquid from the receiving tank to the pressure tank through pipelines, or required installation pressure determined by the expression:

The characteristic of a pumping unit is the dependence of the required pressure on the fluid flow. Geometric head H g, pressure p n and p n do not depend on consumption. Hydraulic losses are a function of flow and depend on the driving mode. In laminar mode, the pipeline characteristic is depicted as a straight line; with turbulent movement in rough pipes, there is a loss of pressure, and therefore the characteristic has the form of a parabola.

Figure 2.8 shows a diagram of the pumping unit and its characteristics. The pump operates in a mode in which the required pressure is equal to the pump pressure. To determine the operating mode of the pump, it is necessary to plot the characteristics of the pump and the pumping unit on the same graph on the same scale. The point of intersection of characteristics is called operating point.

Question No. 42. Parallel and sequential operation of centrifugal pumps.

Parallel operation of pumps is called simultaneous supply of pumped liquid by several pumps to a common pressure manifold. The need for parallel operation of several identical or different pumps arises in cases where it is impossible to provide the required water flow with the supply of one pump. In addition, since water consumption in the city is uneven by hour of the day and by season of the year, the supply pumping station can be adjusted by the number of simultaneously operating pumps.

When designing the combined operation of centrifugal pumps, it is necessary to have a good knowledge of their characteristics; Pumps should be selected taking into account the characteristics of the pipeline.

Centrifugal pumps can operate in parallel provided the developed pressure is equal.

If one of the pumps has a lower pressure than the others, then it can be connected for parallel operation only within the recommended operation range. As the pressure in the system increases, this pump can take part in the operation, but its efficiency will decrease. When the maximum pressure is reached, the pump flow will be equal to 0. A further increase in the pressure in the system will lead to the closure of the check valve and the pump being switched off from operation. Therefore, for parallel operation, pumps of the same type with equal or slightly different pressures and flows should be selected.

Various parallel pump operation schemes are often used for water supply and pumping Wastewater, where it is advisable to combine the supply from several pumps or stations into a common collector. Calculation of the operating mode for such schemes can be done analytically or graphically. In the practice of designing pumping stations, the graphical method is most widely used.

When operating pumps in parallel in a network, the following configuration options for the “pumps - network” system are possible:

the system operates several pumps with the same characteristics;

the system operates several pumps with different characteristics;

the pumps are connected to a common pipeline at a close distance from each other, i.e., the pressure loss from the pump to the pressure conduit is considered equal for all installed pumps, or the pumps are located at a sufficiently large distance from each other, i.e., the difference in pressure loss from pump before connecting to a common pressure pipeline must be taken into account.

Parallel operation of several pumps with the same characteristics. When constructing the characteristics of several parallel operating pumps on a common pressure pipeline, the pump flows at equal pressures are summed up.

If pumps with a flat characteristic Q - H are installed at the pumping station and they are located asymmetrically relative to the pressure pipeline, then in order to determine more accurate operating points for each pump during parallel operation, it is necessary to construct the given characteristics Q - I, for which the characteristics of the suction and pressure pipelines within the pumping station and subtract the ordinates of the obtained characteristics from the ordinates of the characteristics of the corresponding pumps.

Parallel operation of pumps located at different pumping stations. In water supply systems with several power sources, a scheme is used to supply water by several pumping stations to common collectors. In this case, it is necessary to calculate a system of parallel operating pumps located at different pumping stations.

Similar schemes are often used when pumping wastewater from individual sewerage areas into the pressure pipeline of another sewage pumping station. Such schemes can significantly reduce the length of pressure pipelines and reduce capital costs.

To calculate the system, it is necessary to determine the characteristics of parallel operation of pumps installed at each station. This calculation is made in the same way as for parallel operating pumps installed at close distances from each other. Then the reduced characteristics are constructed for the point of exit of the pressure water pipelines from the pumping station.

Sequential operation of pumps is called when one pump (I stage) supplies the pumped liquid to the suction pipe (sometimes into the suction pipeline) of another pump (II stage), and the latter supplies it to the pressure water conduit

In the design and construction of pumping stations, sequential operation of pumps is used in cases where liquid is supplied through pipes over very long distances or to great heights. In some cases, liquid can only be pumped using pumps operating in series. So, for example, at pumping stations that pump sludge, at the moment the working pump is started, it is necessary to create a pressure that exceeds the pressure developed by the pump, and which can be created by operating two pumps in series. A series connection is also used in cases where it is necessary to increase the pressure at a constant (or almost constant) flow rate, which cannot be done with one pump.

Let us consider the case of sequential operation of two centrifugal pumps of the same type installed next to each other.

The pressure of one pump is not sufficient even to lift water to the geometric height #g. When connecting a second pump of the same type with the same characteristic, it turns out that the pumps develop a pressure sufficient to raise water to a height #g and overcome the resistance in the pipeline at a given flow.

The operational point of operation of series-connected pumps is determined by point K, obtained by intersecting the total characteristic Q - #1+ts with the characteristic of the pipeline Q -#tr.

If the pumps are installed in series at one station, then when constructing the pipeline characteristics it is necessary to take into account the losses in the section from the pressure pipe of the pump / to the suction pipe of the pump // and make an amendment to the characteristic Q - #ts. It is unacceptable to ignore losses in the connecting section, since usually the diameters of the fittings and pipeline connecting the pumps are taken equal to the diameter of the suction pipe of the pump //. Due to the high speeds of fluid movement, the pressure loss in this area is relatively large. For the same reason, it is necessary to strive to simplify the connecting pipeline as much as possible, avoiding turns if possible. It should be noted that connecting pumps in series is usually less economical than using a single pump.

Two pumps connected in series are driven as follows. When valves 1 and 2 are closed, pump / is turned on. After the pump / has developed a pressure equal to the pressure when the valve is closed, open the valve / and start the pump //. When the pump // develops a pressure equal to the pressure of 2#o, open valve 2.

When operating pumps in series, pay attention Special attention on the choice of pumps, since not all of them can be used for consistent operation according to the housing strength conditions. These conditions are specified in the technical data sheet of the pump. Typically, series connection of pumps is allowed in no more than two stages.

Series-connected pumps can be located in one machine room, significantly reducing operating costs and capital investments in the construction of the station building, but in this case it is necessary to install increased strength fittings and make more massive pipe fastenings and stops. Therefore, sometimes it is more advisable to place pumps at a distance from each other when transporting water over long distances.

The operation of each pump is characterized by a number of interconnected quantities, such as: productivity, pressure, speed, efficiency, power requirement.

Pumping units are often combinations of centrifugal pumps with asynchronous three-phase alternating current electric motors, which do not allow their speed to be adjusted.

A change in the speed of a centrifugal pump can take place, for example, when it is driven by an internal combustion engine or by means of a belt drive with the possibility of changing the diameter of the pulley. Motors direct current allow you to change the speed, but have very limited use.

The operation of a pump at a certain number of revolutions is characterized by a very specific QH curve, which graphically expresses the relationship between the productivity and pressure developed by the pump. Moreover, as follows from the above:

.

The latter represents the equation of a parabola with a parameter:

The operation of the pump is also characterized by an efficiency curve depending on Q and a power requirement curve depending on Q. As can be seen from what follows, Q and H for a given n are set in connection with the operation of the network.

The total height of the pressure overcome consists of a static (geometric) part and a dynamic part - resistance in pipelines, which changes with changes in the amount of pumped liquid.

If we construct the geometric height of the rise H in rectangular coordinates (parallel to the abscissa axis), at each point of this line we plot vertically (Fig. 24) segments equal to losses in the pipeline (network) when supplying corresponding amounts of liquid, then we obtain a parabolic curve characterizing the work pipeline (network). The pump must provide the pressure necessary to pass a certain flow rate through the network.

When superimposing the QH curve of the pump and the curve characterizing the operation of the network, point B of the intersection of these curves will determine the maximum flow of this pump when operating in a given pipeline (network). Lower productivity can be obtained by partially extinguishing the excess pressure on the valve; so, for example, if it is desirable to obtain productivity Q 2, then the required pressure should be H 2 ", and the pressure developed by the pump is H 2, therefore part of the pressure equal to H 2 - H 2 " should be extinguished when the valve is partially closed required to reduce Q 1 to Q 2. If you want to obtain a performance greater than Q 1 for example Q 3, it is necessary to develop the pressure H 3 "with the pump, and the pump at this performance develops the pressure H 3

In fig. 25 shows a diagram of the parallel operation of two pumps, and FIG. 26 - characteristics of the pump operation when the wheels are connected in parallel (double, triple pump). The total flow rate Q is equal to the sum of the flow rates of all wheels; the pressure developed by the pump varies within the same limits as the pressure developed by each wheel (the abscissas add up at the same ordinates).

When several pumps operate in the same pipeline (network) (parallel operation), the determination of operating points B is especially important. Considering that when two pumps operate, i.e., with double the amount of water, and when three pumps operate, i.e., with triple the amount of water, losses will increase by approximately 4 times (2 2) in the first case and approximately 9 times (3 2) in the second, we artificially reconstruct the loss curves for the case of operation of two and three pumps (Fig. 27), for which we set aside loss segments from the line of geometric pressure for the corresponding capacities, 4 times (with two pumps) and 9 times ( with three pumps) greater than with one pump.

A diagram of the sequential operation of two pumps is shown in Fig. 37.

The idea of ​​sequential operation of centrifugal pumps is reflected to some extent in the multi-wheel pump type. In fig. Figure 38 shows the characteristics of pumps with one, two and three identical wheels. The ordinates increase according to the number of wheels, the abscissas are the same.

The idea of ​​sequential operation is reflected in some designs of units that develop very high pressures. Multi-chamber pump with a capacity of 3000 l/min and a head of 728 m, shown in Fig. 39 appears to be divided into two parts connected in series, driven by a common motor; The water leaving the pressure fitting of the first part of the unit flows to the suction fitting of the second part and leaves the pressure fitting of this part of the unit with a pressure equal to the sum of the pressures caused by the operation of the first and second parts of the pump.

The arrangement of pumps driven by separate engines is called sequential when the pressure pipeline coming from the first is connected to the suction connection of the second; in this case, the pressures developed by both pumps are summed up (less losses in the pipeline connecting them).

Pumps are connected in series if there is a desire to increase the pressure of water supplied to any particular zone (if it is necessary to have sewer pumps with significant pressure, sometimes they design the installation of two pumps located in series; the operation of sewer pumps becomes more complicated).

Question No. 43. Selection of a centrifugal pump.

It is one of the most ancient. Mechanical displacement of a liquid medium can be called the simplest implementation of the pumping principle. Nowadays, the designs of such units, of course, have a more complex structure compared to the first representatives of the class. In its modern form, a piston liquid pump has a durable housing, a developed element base and provides ample opportunities for communication. The latter aspect determines the distribution of equipment in various areas from domestic needs to highly specialized industrial sectors.

Pump device

The basis of the unit is a metal cylinder, in which working processes with liquid take place. Physical manipulation is performed by a piston containing valves. Experts also call such a system a plunger system, based on the type of piston mechanisms used. In essence, the main function in such systems is performed by a piston liquid pump, which operates on the principle of reciprocating motion, although it differs from classical hydraulic motors in the presence of a valve distribution system. The structure of the drive mechanism also includes a whole range of service parts and components. The parts of this design include the crank and connecting rod, which form the basis of the power working body.

Operating principle

In a simplified form, the function of such units resembles a conventional syringe or a water intake column, in which the carrier is replaced by a valve. But, there are also features that a piston liquid pump has. The principle of operation in this case provides that the receiving pipeline will also have a closing valve. Thanks to this device, liquid cannot flow back into the cylinder.

Despite the simple workflow scheme, such pumps have one significant drawback. The fact is that reciprocating actions do not imply a uniform and smooth supply of the media. The erratic rates at which a piston liquid pump operates can present challenges for downstream maintenance of receiving services. However, the use of several pistons allows us to minimize this disadvantage.

Double acting models

The appearance of this type of piston pump is due to the desire of manufacturers to eliminate the pulsation effect, which occurs precisely because of the rhythm in which the piston pushes out portions of liquid. In such pumps, the rod and piston cavities have individual valve systems. This principle of water supply distribution allows not only to eliminate pulsation, but also to increase productivity. True, one-way liquid piston pumps still have their advantages, which are expressed in a higher degree of reliability and durability. Another modification that was supposed to eliminate the rhythmic supply of fluid is a pump supplemented with a hydraulic accumulator. At the moment of peak pressure, such units collect energy, and when it decreases, on the contrary, they release it. However, it is not always possible to completely eliminate pulsation and operating companies have to appropriately develop liquid intake configurations outside the pump design.

Purpose of pumps

Such units are used in different areas. Its principle of operation does not involve working with large volumes of media, but it has many other useful qualities. Since during the displacement of each new “dose” the piston receives a new liquid under dry cylinder conditions, the use of the design is justified in the chemical industry. The specialized purpose of piston liquid pumps allows work with aggressive media, explosive mixtures and certain types of fuel. But the use of piston units is not limited to this. They are also used for domestic needs, for supplying clean water and irrigation. Again, such models are not designed for large circulation volumes, but are distinguished by their reliability and gentle handling of the liquid being served - in fact, this factor has led to the widespread use of pumps in the food industry.

Advantages and disadvantages of the design

Among the advantages of such systems is the durability of the design. This is explained not only by the use of high-strength materials for the manufacture of components, but also by the operating principle itself. In addition, the piston liquid pump is distinguished by its ability to work with media that have high requirements for starting conditions. In particular, many experts note the benefits of “dry” suction, which not every pump can provide. As for the disadvantages, they mainly relate to low performance. Of course, it is theoretically possible to expand the technical parameters of the unit, but this will lead to increased operational requirements of the equipment. Moreover, many alternative designs can provide sufficient productivity at lower costs.

Conclusion

Pumps of this type occupy a separate place on the market, satisfying both the needs of private users and the needs of large enterprises. In modern modifications, the piston liquid pump allows you to perform a wide range of tasks. Some of them may well implement units of other types, but there are areas in which it is impossible to do without the hydraulic principle of pumping. This applies to the mentioned sectors of the chemical and food industries. On the other hand, the demand for piston pumps in everyday life is due to their simple design and undemanding maintenance. And this is not to mention the high operational life of this equipment.

A piston pump for water is used for pumping liquid from wells and wells, the depth of which does not exceed 10 m. Such a device is significantly superior to centrifugal models in terms of the required energy costs and its productivity.

In addition, in small summer cottages where water sources are located very far from the power grid, it is more profitable to use manual piston pumps.

1 Design and principle of operation of a piston pump

Piston-based water pumps are used when a larger type of liquid pump or high-pressure pumps are not cost-effective to use in a small area.

It can be used in an autonomous water supply system from a well, or you can use a manual version. A manual piston pump is used if there is no light in the country or the water consumption is not too large or for a plant sprayer.

The design of a piston water pump is very simple and almost identical to a car piston.

It consists of the following elements:

• cylindrical body;
• stock;
• piston;
• inlet pipe;
• valve in the bottom cover of the device;
• outlet pipe.

The piston is located inside a cylindrical body. In the top cover of the housing there is a hole (flange) with a special rubber gasket. A rod passes through the hole, one edge of which is welded to the piston. The rubber gasket is responsible for the tightness of the cylinder and maintains high pressure in it.

1.1 Operating principle of piston pumps (video)

1.2 Operating cycle

The piston has a check valve. It lets water in but prevents it from coming out. Exactly the same valve is located inside the inlet tube in the lower cylinder cover. When the rod rises up, it pulls the piston along with it. In this case, an area of ​​​​discharged pressure is formed in the sub-piston space, into which water is sucked through the lower valve. Then the piston begins to move downward, creating pressure on the lower valve. It closes and water is forced through the top valve into the space above the piston.

The second cycle of upward movement of the piston forces the liquid into the outlet tube. From there it enters the water supply system and moves to the tap, after which the entire work cycle is repeated again. The inlet tube of the device is usually made of rigid materials, since it should not stick together under the influence of retracting force. For this purpose, a reinforced hose or plastic pipeline is used.

A high-pressure liquid piston pump, unlike deep-well devices, is installed above the entrance to a well or well. And suction occurs through a long hose. In this case, the rod is fixed to the hydraulic motor if the model is an electric pump, or on a metal rocker if a manual water pump was purchased.

The valves of the device are usually either a ball or a membrane in a diaphragm piston type pump. In the first case, a ball made of glass, hard plastic or hard rubber is used as a flap for a conical hole. The peculiarity of the membrane type is that a rubber plate fixed on one side is used as a flap.

The maximum depth from which a piston pump with this design draws water does not exceed 8 meters. If the water surface is lower relative to the location of the device, atmospheric pressure will prevent injection. There are models for deep reservoirs, but their design is different. Their duralumin rod does not enter through a flange, but through an outlet tube on the top cover. This device increases the pressure in the cylinder and lifts water from a depth of up to 30 meters. The device operates when immersed in water depth of 1.5 m.

2 Classification of piston pumps

The distribution of units by type is carried out based on the design and operating principle of the mechanism. The first feature by which piston pumping equipment is divided is the type of drive. In this regard, mechanical and manual options stand out.

A piston hand pump uses a rocker arm connected to a rod on one side as a drive.

In mechanical models there is also distribution. The drive here is an electric motor. But the transmission of torque is carried out either directly to the rod, or using a crank mechanism. The motor itself is located separately from the device in places inaccessible to moisture.

Regarding the piston type, There are three types of devices:

1. Liquid piston type. In such devices, a standard flat piston with a valve acts as a working element.
2. . A mechanical hydraulic pump that uses a plunger (cylindrical piston).
3. Diaphragm type. On such devices, a gasket is installed on top of the standard piston, isolating it from the pumped liquid. This type of design is used by mud pumps and drilling piston units. The body is generously lubricated with oil or emulsion.

Radial piston pump - operating principle

According to the principle of operation, piston units are divided into:

1. Single. They represent a standard operating cycle and supply water in spurts.
2. Double action devices. In this case, two working chambers are used. In this case, in one revolution there are two cycles of liquid injection at once. Ensures uniform feeding.
3. Differential units have two chambers. Moreover, both valves (working and inlet) are located in the same chamber.

Depending on the purpose of the device and the required supply volume, one, two or several pistons are installed on piston-type pumps. There are models with different numbers of cylinders. In this case, a crank mechanism is used for the drive. Pistons, depending on their size, can be small (diameter up to 50 mm), medium (from 50 to 150 mm) and large (diameter exceeds 150 mm).

The type and structure of pumping units also vary depending on the liquid with which the device operates.

In this regard, the following stand out:

1. Cold water pumps. Standard mechanisms designed for pumping water from wells and wells. The temperature of the liquid should not exceed 45 degrees.
2. Models for pumping out hot water. Used for liquids with temperatures above 45 degrees. They differ in alloys that are not subject to thermal effects.
3. Piston-type acid units are designed to work with aggressive chemicals. The mechanisms of the device are made of high-strength materials that do not react with acids.
4. Drilling pumps. Used for drilling oil wells and canals in clay soil. In this case, a piston pump pumps out clay and dirt while drilling. Used as a component of a drilling rig.

In addition to conventional piston installations, combined types are often found. On them, the standard piston operating principle coexists with other types. As a result, they complement each other. An example of such a combination is piston rotary pumps.

In a rotary piston pump, in addition to the translational movement of the piston, the rotational movement of the rotor is used. The result is a stable and uniform flow of liquid. At the same time, the power of the device increases significantly. The operating principle is identical for axial piston adjustable pumps and hydraulic motors.

Some types of axial piston pumps and hydraulic motors are used on large agricultural machinery and other equipment. They are designed to regulate the hydraulic drive of machines.

2.1 The most popular models of piston pumping equipment

Despite the simplicity of design, efficiency and rarity of piston pumps, their popularity on the market is not very high. Therefore, some products of this type are supplied to markets by domestic producers.

An example of popular pumping equipment is the piston unit R 3 80 s. This is a universal model that is used for pumping water in open spaces, for work indoors and on ships. Pumps water, gasoline, oil. Equipped with a manual drive.

The technical characteristics of the device are as follows:

• cylinder body diameter – 80 mm;
• stroke of the working piston inside the cylinder – 80 mm;
• increased liquid, absorbs water from a depth of 5.5 m;
• the device is of a dual action type;
• per cycle, 0.74 liters of liquid are supplied.

Another model is produced by the Russian manufacturer Livgidromash. The AN 2 16 piston pump uses two pistons and two cylinders. The drive is a belt drive from an electric motor. This is mounted on a load frame.

The model comes in several configurations. Some of them are used as a pump for fresh technical water from a well. Others pump gasoline and other liquids. Pump use as a nutrient element for heating circuits.

The equipment has the following performance characteristics:

• operating power of the electric motor – 1.5 kW;
• liquid supply is 2 m3 per hour;
• number of piston strokes per minute – 165;
• the device provides pressure over an area of ​​160 m;
• weight – 110 kg.

To supply drinking water from a well, manual options are most often used, which are manufactured by Ukrainian and Russian manufacturers. Popular series: Economy, Optima K, Country, Style. The average cost of such speakers is from 5 to 10 thousand rubles. Models with a large depth of water pumping (up to 36 m) cost about 30-35 thousand rubles.