The need to classify gas pipelines came into our lives with the widespread spread of technologies for using gas for the needs of the population. Heating of residential, administrative, and industrial buildings, the use of gas both in cooking and in production has long become a common thing for us.

The classification of gas pipelines is necessary measures and rules for systematization laying gas lines. may differ both in their purpose and in a number of indicators, such as: pressure, the material from which it is made, location, volumes of transported gas and others.

Contents of the article

About the types of classification according to the purpose of the highway

Due to the characteristic specifics of their use, gas pipes can be classified in several directions at once. After this, for an individual gas pipeline, a number of characteristics can be compiled that determine its properties and design features.

Special reference signs located along the entire gas pipeline route can tell us about this in detail. They are sign boards measuring 140x200 millimeters, with encrypted information about the gas pipeline.

Common in green (for steel options) and yellow ( polyethylene pipes) color version. Signs can be placed on the walls of buildings, as well as on special posts near the routes. These signs are installed at a distance of no more than 100 meters from each other, maintaining a line of sight zone.

When planning gas pipes can be distinguished: street, intra-block, inter-shop and yard. The characteristics of the location do not end there, because laying and inserting communications is possible on the ground, underground and above the ground.

In the gas supply system, gas pipelines can be classify according to their intended purpose:

• distribution These are external gas pipelines supplying gas from gas sources to distribution points, and in addition gas pipelines of medium and high pressure, connected to one object;
• gas pipeline-inlet. This is the section from the connection to the gas distribution pipeline to the inlet device that turns off the system;
• inlet gas pipeline. This is the gap from the shutdown device to the immediate internal gas pipeline;
• inter-village Such communications are laid outside populated areas;
• interior. An internal gas pipeline is considered to be the section that starts from the inlet gas pipeline to the final unit using gas.

Classification of gas pipelines by pressure

The pressure in the pipe is the most important indicator of the functioning of the gas pipeline. By calculating this indicator, it is possible to determine the capacity limit of the gas pipeline, its reliability, as well as the degree of risk that arises during its operation.

A gas pipeline is undoubtedly a potentially dangerous object, and therefore the laying or insertion of gas communications with a pressure exceeding the permissible carries great risks for the gas transportation system and the safety of surrounding people. Proper classification rules will help avoid accidents at explosive sites.

Separate high, medium and low pressure . A more detailed classification of gas pipelines is given below:

• high pressure category I-a. The gas pressure in such a gas pipeline can exceed 1.2 MPa. This type is used to connect to gas system steam and turbine plants, as well as thermal power plants. Pipe diameter from 1000 to 1200 mm;
• high pressure category I. The indicator ranges from 0.6 to 1.2 MPa. Used to transfer gas to gas distribution points. The pipe diameter is the same as the diameter of category I-a;
• high pressure category II. Indicator from 0.3 to 0.6 MPa. Supplied to gas distribution points for residential buildings and industrial facilities. The diameter of the high pressure line is from 500 to 1000 mm;
• medium pressure category III. The indicator can be in the range from 5 kPa to 0.3 MPa. They are used to supply gas to gas distribution points through medium pressure pipes located on residential buildings. Medium pressure pipe diameter from 300 to 500 mm;
• low pressure category IV. A pressure not exceeding 5 kPa is permissible. Such gas pipes supply the carrier directly to residential buildings. Low pressure gas pipelines have a pipe diameter of no more than 300 mm.

Types of gas pipelines by depth

Taking into account the factor of urban conditions, the load from heavy transport, the influence of snow and rain on the ground, the depth of communications in the city and their main variations require consideration of them separately.

The rules for laying gas mains also depend on the type of gas being transported. Pipes supplying dried gas can be laid in the freezing zone of the soil. The depth of installation is determined primarily by the likelihood of mechanical damage to the soil or road surface.

Dynamic loads should not cause stress in the pipes. At the same time, an increase in the laying depth directly proportionally affects the cost of road repair and construction work required when laying pipes.

• on driveways of streets with concrete or asphalt pavement, the minimum laying depth is allowed to be at least 0.8 meters; in the absence of such covering, a laying depth of 0.9 meters is allowed;
• the minimum depth for laying pipes transporting dry gas is assumed to be 1.2 meters from the ground surface;
• on streets and intra-block areas where there is guaranteed to be no traffic and there will be no traffic, the laying rules allow for the laying depth to be reduced to 0.6 meters;
• The depth of the underground gas pipeline depends on the presence of water vapor and the level of soil freezing. When transporting dry gas, the laying depth is usually 0.8 meters.

Laying a gas pipeline in a trench.mp4 (video)

Main gas pipelines and their security zones

Main gas pipelines are entire complexes technical structures, whose main task is to transport gas from the place of its production to distribution points, and then to the consumer. In close proximity to the city they become local. The latter, in turn, serve to distribute gas throughout the city and deliver it to industrial enterprises.

The design and installation of main communications must take into account the volume of gas, the power of the equipment working with it, gas pressure and, of course, the rules for laying main gas pipelines. The location of the main gas pipeline near the facility that needs to be gasified does not mean that the tie-in will be applied specifically to it.

The tie-in can be laid several kilometers from the gasified section. In addition, the tie-in must take into account the practical possibility of providing the consumer with a given power and pressure in the pipe.

Main pipes have different capacities. It is influenced, first of all, by the fuel and energy balance of the area in which the pipeline is planned to be laid. At the same time, it is necessary to rationally determine the annual amount of gas, taking into account the volume of the resource, for the future after the start of operation of the complex.

Typically, the performance parameter characterizes the amount of gas supplied per year. Throughout the year, this figure will fluctuate downward due to the uneven use of gas by the population over the seasons. In addition, this is also affected by changes in ambient temperature.

The security zone of the main gas pipeline implies a section on both sides of the gas pipeline, limited by two parallel lines. Security zones for main gas pipes are mandatory due to the explosiveness of such communications. And therefore it must be carried out taking into account the required distance.

To maintain the required length of security zones, the following rules must be taken into account:

• for high pressure lines. Category I – the security zone is 10 m;
• for high pressure pipes Category II – the security zone is 7 m;
• for medium pressure lines. – the security zone is 4 m;
• for low pressure pipes – the security zone is 2 m.

This characteristic depends on several factors. First of all, this is the diameter of the pipe, as well as the type of liquid, and other indicators.

For hydraulic calculation pipeline, you can use the hydraulic pipeline calculation calculator.

When calculating any systems based on fluid circulation through pipes, there is a need to accurately determine pipe capacity. This is a metric value that characterizes the amount of liquid flowing through pipes over a certain period of time. This indicator is directly related to the material from which the pipes are made.

If we take, for example, plastic pipes, they differ in almost the same throughput throughout their entire service life. Plastic, unlike metal, is not prone to corrosion, so a gradual increase in deposits is not observed in it.

As for metal pipes, they throughput decreases year after year. Due to the appearance of rust, the material inside the pipes peels off. This leads to surface roughness and the formation of even more plaque. This process occurs especially quickly in hot water pipes.

The following is a table of approximate values, which was created to make it easier to determine the throughput of pipes in apartment wiring. This table does not take into account the reduction in throughput due to the appearance of sedimentary build-ups inside the pipe.

Table of pipe capacity for liquids, gas, water vapor.

Type of liquid	Speed ​​(m/sec)
City water
Water pipeline
Water system central heating
Pressure system water in pipeline line
Hydraulic fluid	up to 12m/sec
Oil pipeline line
Oil in the pressure system of the pipeline line
Steam in the heating system
Steam central piping system
Steam in a heating system with high temperature
Air and gas in central system pipeline

Most often, ordinary water is used as a coolant. The rate of decrease in throughput in pipes depends on its quality. The higher the quality of the coolant, the longer the pipeline made of any material (steel, cast iron, copper or plastic) will last.

Calculation of pipe capacity.

For accurate and professional calculations, you must use the following indicators:

• The material from which pipes and other elements of the system are made;
• Pipe length
• Number of water consumption points (for water supply system)

The most popular calculation methods:

1. Formula. A rather complex formula, which is understandable only to professionals, takes into account several values ​​at once. The main parameters that are taken into account are the material of the pipes (surface roughness) and their slope.

2. Table. This is a simpler way by which anyone can determine the throughput of a pipeline. An example is the engineering table of F. Shevelev, from which you can find out the throughput capacity based on the pipe material.

3. Computer program. One of these programs can be easily found and downloaded on the Internet. It is designed specifically to determine the throughput for pipes of any circuit. In order to find out the value, you need to enter initial data into the program, such as material, pipe length, coolant quality, etc.

It should be said that the latter method, although the most accurate, is not suitable for calculating simple household systems. It is quite complex and requires knowledge of the values ​​of a wide variety of indicators. To calculate a simple system in a private house, it is better to use tables.

An example of calculating pipeline capacity.

Pipeline length is an important indicator when calculating throughput. The length of the pipeline has a significant impact on throughput indicators. The greater the distance water travels, the less pressure it creates in the pipes, which means the flow speed decreases.

Here are some examples. Based on tables developed by engineers for these purposes.

Pipe capacity:

• 0.182 t/h with a diameter of 15 mm
• 0.65 t/h with pipe diameter 25 mm
• 4 t/h with a diameter of 50 mm

As can be seen from the examples given, a larger diameter increases the flow rate. If the diameter is doubled, the throughput will also increase. This dependence must be taken into account when installing any liquid system, be it plumbing, drainage or heat supply. Especially it concerns heating systems, since in most cases they are closed, and the heat supply in the building depends on the uniform circulation of the liquid.

GAS NETWORKS

Modern distribution systems natural gas supplies are a complex complex of structures consisting of gas distribution stations, gas networks for various purposes, gas control points and installations, backup systems and gas combustion plants. Each element of the gas supply system has its own tasks and characteristics.

3.1. Estimated gas costs

To design a gas supply system for a populated area, data on annual consumption is required natural gas. This is determined by standards taking into account the development perspective of consumers.

Since the gas supply system has a high cost and high metal consumption, serious attention should be paid to justifying the calculated gas costs. These costs are used to select gas pipeline diameters.

Gas networks must be designed for maximum hourly flow rates. Estimated hourly gas consumption Q r.h, m 3 / h for household needs is determined as a share of annual consumption according to the formula:

Where K tah - hourly maximum coefficient (transition from Q year to the maximum hourly gas consumption).

The estimated hourly gas consumption for the technological needs of industrial and agricultural enterprises should be determined based on the fuel consumption data of these enterprises (taking into account changes in efficiency when switching to gas fuel). Coefficient K max, is the reciprocal of the number of hours per year of use of the minimum (K t ax= 1/m). Magnitude K t ax for industrial enterprises depends on the type of production, technological process and the number of work shifts per day.

For individual residential buildings and public buildings Q r.h is determined by the sum of the nominal gas consumption of gas appliances, taking into account the coefficient of simultaneity of their operation.

(3.2)

Where K 0 - simultaneity factor; q nom - nominal gas consumption of the device, m 3 / h; P- number of similar devices; X - number of types of devices.

3.2. Calculation of gas pipeline diameter and permissible pressure loss

The throughput capacity of gas pipelines can be taken from the conditions for creating, at maximum permissible gas pressure losses, the most economical and reliable system in operation, ensuring the stability of the operation of hydraulic fracturing and gas control units (GRU), as well as the operation of consumer burners in the permissible gas pressure ranges.

The calculated internal diameters of gas pipelines are determined based on the condition of ensuring uninterrupted gas supply to all consumers during hours of maximum gas consumption.

Calculation of the diameter of a gas pipeline should, as a rule, be performed on a computer with an optimal distribution of the calculated pressure loss between sections of the network.

If it is impossible or impractical to perform calculations on a computer (lack of an appropriate program, certain sections of gas pipelines, etc.), hydraulic calculations can be performed using the formulas given below or using nomograms (SP-42-101-2003) compiled using these formulas.

The calculated pressure losses in high and medium pressure gas pipelines are accepted within the pressure category adopted for the gas pipeline.

Calculated total losses gas pressure in low-pressure gas pipelines (from the gas supply source to the most remote device) is assumed to be no more than 180 MPa, including in distribution gas pipelines 120 MPa, in gas inlet pipelines and internal gas pipelines - 60 MPa.

The values ​​of the calculated gas pressure loss when designing gas pipelines of all pressures for industrial, agricultural and household enterprises and public utility organizations are taken depending on the gas pressure at the connection point, taking into account the technical characteristics of the gas equipment accepted for installation, automatic safety devices and automatic control of process mode thermal units.

The pressure drop in a section of the gas network can be determined:

· for medium and high pressure networks according to the formula

(3.3)

Where P H- absolute pressure at the beginning of the gas pipeline, MPa; R K- absolute pressure at the end of the gas pipeline, MPa; P 0 = 0.101325 MPa; λ - coefficient of hydraulic friction; l- estimated length of a gas pipeline of constant diameter, m; d- internal diameter of the gas pipeline, cm; ρ 0 - gas density under normal conditions, kg/m3; Q 0- gas consumption, m 3 /h, under normal conditions;

· for low pressure networks according to the formula

(3.4)

Where P H- pressure at the beginning of the gas pipeline, Pa; R K - pressure at the end of the gas pipeline, λ, l, d, ρ 0 , Q 0- the designations are the same as in the previous formula.

Hydraulic friction coefficient λ determined depending on the mode of gas movement through the gas pipeline, characterized by the Reynolds number,

(3.5)

Where ν - coefficient of kinematic viscosity of gas, m 2 /s, under normal conditions; Q 0 , d - the designations are the same as in the previous formula, and the hydraulic smoothness of the inner wall of the gas pipeline, determined by the condition

where Re is the Reynolds number; P- equivalent absolute roughness of the inner surface of the pipe wall, taken equal for new steel - 0.01 cm, for used steel - 0.1 cm, for polyethylene, regardless of the time of operation - 0.0007 cm; d- the designation is the same as in the previous formula.

Depending on the value of Re, the coefficient of hydraulic friction λ defined:

· for laminar mode of gas movement Re< 2000

· for critical gas movement mode Re = 2000-4000

(3.8)

· for Re > 4000 - depending on the fulfillment of condition (3.6);

· for a hydraulically smooth wall (inequality (3.6) is true):

· at 4000< Rе < 100000 по формуле

· at Re > 100000

(3.10)

· for rough walls (inequality (6) is unfair) for Re > 4000

(3.11)

Where P - the designation is the same as in formula (3.6); d- the designation is the same as in formula (3.4).

The estimated gas consumption in sections of low-pressure external gas distribution pipelines that have gas travel costs should be determined as the sum of transit and 0.5 gas travel costs in this section.

The pressure drop in local resistances (elbows, tees, shut-off valves, etc.) can be taken into account by increasing the actual length of the gas pipeline by 5-10 %.

For external above-ground and internal gas pipelines, the estimated length of gas pipelines is determined by the formula

(3.12)

Where l- actual length of the gas pipeline, m; - the sum of the local resistance coefficients of the gas pipeline section; d- the designation is the same as in formula (3.4); λ - coefficient of hydraulic friction, determined depending on the flow regime and hydraulic smoothness of the walls of the gas pipeline according to formulas (3.7) - (3.11).

Calculation of ring networks of gas pipelines should be carried out by linking gas pressures at the nodal points of the calculation rings. The problem of pressure loss in the ring is allowed up to 10 % .

When performing hydraulic calculations of overhead and internal gas pipelines, taking into account the degree of noise created by gas movement, gas movement speeds should be taken as no more than 7 m/s for low-pressure gas pipelines, 15 m/s for medium-pressure gas pipelines, 25 m/s for high-pressure gas pipelines .

When performing hydraulic calculations of gas pipelines, carried out using formulas (3.5)-(3.12), as well as using various methods and programs for electronic computers compiled on the basis of these formulas, the calculated internal diameter of the gas pipeline should first be determined using the formula

(3.13)

Where d- design diameter, cm; A, B, t, t 1 - coefficients determined in Tables 3.1 and 3.2 depending on the network category (pressure) and gas pipeline material; Q 0 - estimated flow rate gas, m 3 / h, at

normal conditions; ΔР UD- specific pressure loss (Pa/m - for low pressure networks, MPa/m - for medium and high pressure networks), determined by the formula

Permissible pressure loss (Pa - for low pressure networks, MPa/m - for medium and high pressure networks); L- distance to the most distant point, m.

Table 3.1

Table 3.2

The internal diameter of the gas pipeline is taken from the standard range of internal diameters of pipelines: the nearest larger one is for steel gas pipelines and the nearest smaller one is for polyethylene ones.

3.3. Calculation of high and medium pressure gas networks.

3.3.1. Calculation of branched distribution gas pipelines of high and medium pressure

The hydraulic operating modes of gas distribution pipelines must be adopted from the conditions for creating a system that ensures the stability of the operation of all gas distribution stations, hydraulic fracturing units, and burners within the permissible limits of gas pressure.

Calculation of gas pipelines comes down to determining the required diameters and checking the specified pressure drops.

The calculation procedure may be as follows.

1 . The initial pressure is determined by the operating mode of the gas distribution system or hydraulic fracturing unit, and the final pressure is determined by the passport characteristics of consumer gas appliances.

2. Select the most distant points of branched gas pipelines and determine the total length l 1 according to selected

main directions. Each direction is calculated separately.

3. Determine the estimated gas costs for each section of the gas pipeline Qp.

4. By values Q p By calculation or according to nomograms SP 42-101-2003, the diameters of the sections are pre-selected, rounding them up.

5. For selected standard diameters find the actual values ​​of the pressure drop and then refine P K.

6. Pressures are determined starting from the beginning of the gas pipeline, because the initial pressure of the hydraulic fracturing system or hydraulic fracturing is known. If the pressure R K the actual value is significantly greater than the specified one (more than 10%), then the diameters of the final sections of the main direction are reduced.

7. After determining the pressures in this main direction, carry out hydraulic calculation gas pipeline branches using the same method, starting from the second point. In this case, the pressure at the sampling point is taken as the initial pressure.

3.3.2. Calculation of ring gas networks of high and medium pressure

All city networks rely on a given pressure drop. The calculated drop for a high (medium) pressure network is determined from the following considerations. Initial pressure (R n) is taken to be maximum according to SNiP, and the final pressure (R k) such that when maximum load the network was provided with minimal permissible pressure gas in front of the regulators at the hydraulic fracturing station. The value of this pressure is the sum of the maximum gas pressure in front of the burners, the pressure drop in the subscriber branch at maximum load, and the pressure drop in the gas distribution system. In most cases, it is enough to have an excess pressure of 0.15÷0.20 MPa in front of the pressure regulators.

When calculating ring networks, it is necessary to leave a pressure reserve to increase the throughput of the system in emergency hydraulic conditions. 100% supply of gas to consumers in the event of failures of system elements is associated with additional capital investments.

The maximum effect can be achieved with the following formulation of the problem. Due to the short duration of emergency situations, a decrease in the quality of the system should be allowed when its elements fail. The decline in quality is assessed by the security ratio To about, which depends on the category of consumers. The volumetric flow rate of gas supplied to the consumer during emergency mode will be determined from the ratio

Where . - calculated consumer gas consumption, m 3 /h.

The supply coefficient for municipal consumers can be taken as 0.80÷0.85, for heating boiler houses 0.70 ÷ 0.75. After justification K about For all consumers, the necessary network capacity reserve is determined.

High (medium) pressure networks usually consist of one ring and a number of outlets to gas control points. The calculation is made for three modes: normal and two emergency, when the head sections on both sides of the power point are turned off, and the gas flows in one direction at reduced loads. Network diameters are taken to be the maximum of two emergency modes.

The procedure for calculating one ring network is as follows.

1. A preliminary calculation of the diameter of the ring is made using the formulas of section 3.2.

2. Two options for hydraulic calculation of emergency modes are performed. The diameters of the sections are adjusted so that the gas pressure at the last consumer does not drop below the minimum permissible value. For all branches, the diameters of gas pipelines are calculated to fully utilize the pressure drop with the supply of gas

3. Calculate the distribution of flows under normal conditions and determine the pressure at all nodal points.

4. The diameters of branches to concentrated consumers are checked during an emergency hydraulic mode. If the diameters are insufficient, they are increased to the required sizes.

3.4. Calculation of low pressure gas networks

3.4.1. Calculation of branched low pressure gas distribution pipelines

Consumers are usually connected directly to urban low-pressure networks. Fluctuations in gas pressure among consumers depend on the magnitude of the calculated pressure drop (∆) and the degree of its use along the path of gas movement from the supply point to the gas appliance. Depending on the accepted gas pressures in front of household gas appliances, the maximum gas pressures in gas distribution pipelines after hydraulic fracturing are set: 0.003 MPa at a nominal pressure (∆) of devices of 0.002 MPa and 0.002 MPa at a nominal pressure of devices of 0.0013 MPa.

When calculating gas pipelines, it is advisable to use nomograms constructed according to calculation formulas(see Appendix B SP 42-101-2003).

Standard procedure for calculating a gas network.

1. The initial and final pressures are taken according to the hydraulic fracturing operating mode and the characteristics of gas appliances.

2. The pressure drop in low pressure gas pipelines should be determined depending on Re.

3. Determine the estimated gas costs for sections Q p ., i ,.

4. Select the most distant points of the system and calculate , for each direction.

5. A hydraulic calculation of gas pipelines is carried out to determine the diameter and pressure drop according to the formulas of section 3.1.2.

Taking into account the degree of noise created by gas movement in low-pressure gas pipelines, gas movement speeds should be taken no more than 7 m/s.

where is the actual length of the gas pipeline, m; MC - estimated length of the local resistance section; - the sum of the local resistance coefficients of a gas pipeline section length l, m.

7. Using the nomograms of Appendix B SP 42-101-2003, the actual values ​​of pressure drops for each section are determined.

8. Determine the total pressure loss in the entire direction

and compare them with the given ones.

If the deviation from the accepted value is more than 10%, the diameter of the gas pipelines is changed, starting from the final sections of the main directions.

3.4.2. Calculation of low pressure ring gas networks

The procedure for carrying out network calculations.

1. Select the main directions of gas flows and determine the most distant end points.

2. Determine the concentrated and specific travel costs of gas for all circuits of the gas network.

3. Determine travel, transit and estimated gas costs by section.

4. Based on the given pressure drop in the network for the main directions, the values ​​of ∆P are estimated

During pipeline design, the choice of pipe sizes is carried out on the basis of a hydraulic calculation, which determines the internal diameter of the pipes to pass the required amount of gas with allowable pressure losses or, conversely, the pressure loss when transporting the required amount of gas through a log house of a previously specified diameter. The resistance that is provided to the movement of gas in the pipeline is summed up from local resistances and linear friction resistances: friction resistances play their role along the entire length of the pipeline, and local resistances are created only at the point of changes in the direction and speed of gas movement (tees, corners, etc. ). Detailed hydraulic calculation of gas pipelines is carried out according to the formulas given in SP 42-101-2003, which also takes into account the mode of gas movement and the hydraulic resistance coefficients of the gas pipeline.
***
You can also use Online calculations to calculate the diameter of the gas pipeline and its dimensions. A shortened version is provided here.
***

To calculate the internal diameter of a gas pipeline, you can use the formula:

DP= (626AQ0/ρ0 ΔPsp)1/m1

DP – design diameter. Q0 – calculated gas flow (m3/h). ΔРу – specific pressure loss (Pa/m)

The internal diameter of the gas pipeline is taken from the standard internal diameters of pipelines: the nearest smaller one is for polyethylene gas pipelines and the nearest larger one is for steel ones.

In low-pressure gas pipelines, the calculated total gas pressure loss is taken to be no more than 1.80 * 10 (to the third power) PA, in internal gas pipelines and gas inlet pipelines - 0.60 * 10 (to the third power) PA.

In order to calculate the pressure drop, it is necessary to determine a parameter such as the Reynolds number, which depends on the nature of the gas movement. It is also necessary to determine “λ” - the coefficient of hydraulic friction. The Reynolds number is a dimensionless ratio that reflects the mode in which a gas or liquid moves: turbulent and laminar.

There is a so-called critical Reynolds number, which is equal to 2320. If the Reynolds number is less than the critical value, then the regime is laminar, if more, then it is turbulent.

The Reynolds number, as a criterion for the transition from laminar to turbulent and vice versa, is relevant for pressure flows. If we consider the transition to free-flow flow, then here the transition zone between the turbulent and laminar regime increases, so it is not particularly necessary to use the Reynolds number as a criterion.

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Pipe throughput: simple about complex things

How does the capacity of a pipe change depending on the diameter? What factors besides cross section, affect this parameter? Finally, how to calculate, even approximately, the permeability of a water pipeline with a known diameter? In this article I will try to give the most simple and accessible answers to these questions.

Our task is to learn how to calculate the optimal cross-section of water pipes.

Why is this necessary?

Hydraulic calculation allows you to obtain optimal minimum water pipe diameter value.

On the one hand, there is always a catastrophic shortage of money during construction and repairs, and the price per linear meter of pipes increases nonlinearly with increasing diameter. On the other hand, an undersized water supply section will lead to an excessive drop in pressure at the end devices due to its hydraulic resistance.

When the flow rate is at the intermediate device, the pressure drop at the end device will lead to the fact that the water temperature with the cold water and hot water taps open will change sharply. As a result, you will either be doused with ice water or scalded with boiling water.

Restrictions

I will deliberately limit the scope of the problems under consideration to the water supply of a small private house. There are two reasons:

1. Gases and liquids of different viscosities behave completely differently when transported through a pipeline. Consideration of the behavior of natural and liquefied gas, oil and other media would increase the volume of this material several times and would take us far from my specialization - plumbing;
2. In the case of a large building with numerous plumbing fixtures, for the hydraulic calculation of the water supply it will be necessary to calculate the probability of simultaneous use of several water points. IN small house the calculation is performed for peak consumption by all available devices, which greatly simplifies the task.

Factors

Hydraulic calculation of a water supply system is a search for one of two quantities:

• Calculation of pipe capacity for a known cross-section;
• Calculation of the optimal diameter with a known planned flow rate.

In real conditions (when designing a water supply system), it is much more common to perform the second task.

Everyday logic dictates that the maximum water flow through a pipeline is determined by its diameter and inlet pressure. Alas, the reality is much more complicated. The fact is that the pipe has hydraulic resistance: Simply put, the flow is slowed down by friction against the walls. Moreover, the material and condition of the walls predictably influence the degree of braking.

Here full list Factors affecting the performance of a water pipe:

• Pressure at the beginning of the water supply (read - pressure in the line);
• Slope pipes (change in its height above the conditional ground level at the beginning and end);

• Material walls Polypropylene and polyethylene have much less roughness than steel and cast iron;
• Age pipes. Over time, steel becomes overgrown with rust and lime deposits, which not only increase roughness, but also reduce the internal clearance of the pipeline;

This does not apply to glass, plastic, copper, galvanized or metal-polymer pipes. Even after 50 years of operation they are in new condition. The exception is silting of the water supply when large quantities suspensions and the absence of filters at the inlet.

• Quantity and angle turns;
• Diameter changes water supply;
• Presence or absence welds, burr from soldering and connecting fittings;

• Shut-off valves. Even full bore ball valves provide some resistance to flow movement.

Any calculation of pipeline capacity will be very approximate. Willy-nilly, we will have to use average coefficients typical for conditions close to ours.

Torricelli's Law

Evangelista Torricelli, who lived at the beginning of the 17th century, is known as a student of Galileo Galilei and the author of the very concept atmospheric pressure. He also owns a formula that describes the flow rate of water pouring out of a vessel through a hole of known dimensions.

For the Torricelli formula to work, you must:

1. So that we know the water pressure (the height of the water column above the hole);

One atmosphere under Earth's gravity is capable of raising a water column by 10 meters. Therefore, pressure in atmospheres is converted into pressure by simply multiplying by 10.

1. So that there is a hole significantly smaller than the diameter of the vessel, thus eliminating loss of pressure due to friction against the walls.

In practice, Torricelli's formula allows one to calculate the flow of water through a pipe with an internal cross-section of known dimensions at a known instantaneous pressure at the time of flow. Simply put: to use the formula, you need to install a pressure gauge in front of the tap or calculate the pressure drop in the water supply system at a known pressure in the line.

The formula itself looks like this: v^2=2gh. In it:

• v is the flow velocity at the outlet of the hole in meters per second;
• g is the acceleration of the fall (for our planet it is equal to 9.78 m/s^2);
• h is the pressure (the height of the water column above the hole).

How will this help in our task? And the fact that fluid flow through the hole(the same bandwidth) is equal to S*v, where S is the cross-sectional area of ​​the hole and v is the flow velocity from the above formula.

Captain Obviousness suggests: knowing the cross-sectional area, it is not difficult to determine the internal radius of the pipe. As you know, the area of ​​a circle is calculated as π*r^2, where π is taken to be rounded equal to 3.14159265.

In this case, Torricelli’s formula will look like v^2=2*9.78*20=391.2. The square root of 391.2 is rounded to 20. This means that water will pour out of the hole at a speed of 20 m/s.

We calculate the diameter of the hole through which the flow flows. Converting the diameter to SI units (meters), we get 3.14159265*0.01^2=0.0003141593. Now let’s calculate the water consumption: 20*0.0003141593=0.006283186, or 6.2 liters per second.

Back to reality

Dear reader, I would venture to guess that you do not have a pressure gauge installed in front of the mixer. Obviously, for a more accurate hydraulic calculation, some additional data is needed.

Typically, the calculation problem is solved in reverse: given the known water flow through the plumbing fixtures, the length of the water pipe and its material, a diameter is selected that ensures the pressure drop to acceptable values. The limiting factor is the flow rate.

Reference data

The normal flow rate for internal water supply systems is considered to be 0.7 - 1.5 m/s. Exceeding the last value leads to the appearance of hydraulic noise (primarily at bends and fittings).

Water consumption standards for plumbing fixtures are easy to find in regulatory documentation. In particular, they are given in the appendix to SNiP 2.04.01-85. To save the reader from lengthy searches, I will provide this table here.

The table shows data for mixers with aerators. Their absence equalizes the flow rate through the sink, washbasin and shower faucets with the flow rate through the mixer when filling the bathtub.

Let me remind you that if you want to calculate the water supply of a private house with your own hands, add up the water consumption for all installed devices . If these instructions are not followed, you will be in for surprises such as a sharp drop in temperature in the shower when you open the tap. hot water on .

If the building has a fire water supply, 2.5 l/s is added to the planned flow rate for each hydrant. For fire water supply, flow speed is limited to 3 m/s: In the event of a fire, hydraulic noise is the last thing that will irritate residents.

When calculating the pressure, it is usually assumed that at the device farthest from the input it should be at least 5 meters, which corresponds to a pressure of 0.5 kgf/cm2. Some plumbing fixtures (instantaneous water heaters, automatic filler valves) washing machines etc.) simply do not work if the pressure in the water supply is below 0.3 atmospheres. In addition, it is necessary to take into account hydraulic losses on the device itself.

On the picture - instantaneous water heater Atmor Basic. It turns on heating only at a pressure of 0.3 kgf/cm2 and above.

Flow, diameter, speed

Let me remind you that they are linked together by two formulas:

1. Q = SV. Water flow in cubic meters per second is equal to the cross-sectional area in square meters, multiplied by the flow speed in meters per second;
2. S = π r^2. The cross-sectional area is calculated as the product of pi and the square of the radius.

Where can I get the radius values ​​for the internal section?

• U steel pipes with a minimum error it is equal to half the remote control(conditional bore used to mark pipes);
• For polymer, metal-polymer, etc. the internal diameter is equal to the difference between the external one, which is used to mark the pipes, and twice the wall thickness (it is also usually present in the marking). The radius, accordingly, is half the internal diameter.

1. The internal diameter is 50-3*2=44 mm, or 0.044 meters;
2. The radius will be 0.044/2=0.022 meters;
3. The internal cross-sectional area will be equal to 3.1415*0.022^2=0.001520486 m2;
4. At a flow rate of 1.5 meters per second, the flow rate will be 1.5*0.001520486=0.002280729 m3/s, or 2.3 liters per second.

Loss of pressure

How to calculate how much pressure is lost in a water pipeline with known parameters?

The simplest formula for calculating the pressure drop is H = iL(1+K). What do the variables in it mean?

• H is the desired pressure drop in meters;
• i — hydraulic slope of a water pipe meter;
• L is the length of the water pipeline in meters;
• K— coefficient, which makes it possible to simplify the calculation of the pressure drop by shut-off valves And . It is tied to the purpose of the water supply network.

Where can I get the values ​​of these variables? Well, except for the length of the pipe, no one has canceled the tape measure yet.

Coefficient K is taken equal to:

With a hydraulic slope the picture is much more complicated. The resistance offered by a pipe to flow depends on:

• Internal section;
• Wall roughness;
• Flow rates.

A list of values ​​for 1000i (hydraulic slope per 1000 meters of water supply) can be found in Shevelev’s tables, which, in fact, serve for hydraulic calculations. The tables are too large for this article because they provide 1000i values ​​for all possible diameters, flow rates and materials, adjusted for service life.

Here is a small fragment of Shevelev’s table for a plastic pipe measuring 25 mm.

The author of the tables gives pressure drop values ​​not for the internal section, but for standard sizes, which are used to mark pipes, adjusted for wall thickness. However, the tables were published in 1973, when the corresponding market segment had not yet been formed.
When calculating, keep in mind that for metal-plastic it is better to take values ​​corresponding to a pipe one step smaller in size.

Let's use this table to calculate the pressure drop by polypropylene pipe with a diameter of 25 mm and a length of 45 meters. Let's agree that we are designing a water supply system for household purposes.

1. At a flow speed as close as possible to 1.5 m/s (1.38 m/s), the 1000i value will be equal to 142.8 meters;
2. The hydraulic slope of one meter of pipe will be equal to 142.8/1000=0.1428 meters;
3. The correction factor for domestic water supply systems is 0.3;
4. The formula as a whole will take the form H=0.1428*45(1+0.3)=8.3538 meters. This means that at the end of the water supply system, with a water flow rate of 0.45 l/s (the value from the left column of the table), the pressure will drop by 0.84 kgf/cm2 and at 3 atmospheres at the inlet it will be quite acceptable 2.16 kgf/cm2.

This value can be used to determine consumption according to Torricelli formula. The calculation method with an example is given in the corresponding section of the article.

In addition, in order to calculate the maximum flow rate through a water supply system with known characteristics, you can select in the “flow rate” column of Shevelev’s complete table a value at which the pressure at the end of the pipe does not fall below 0.5 atmosphere.

Conclusion

Dear reader, if the given instructions, despite being extremely simplified, still seem tedious to you, just use one of the many online calculators. As always, more information can be found in the video in this article. I would appreciate your additions, corrections and comments. Good luck, comrades!

July 31, 2016

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