The speed of water movement in gravity pipes is assumed to be no less than the speed of water flow in the river.

Standard pipe diameters are accepted, rounding those obtained by calculation downward. Based on the accepted diameter, the actual speed in the gravity pipe is determined, and it must be greater than the calculated one. This speed is then checked at high water levels, i.e. flood, when, to ensure minimal siltation, the full flow is passed through one line.

Accepted diameter of gravity pipelines D (in m) must be checked for silt-free fine sediment transported through the pipe in an amount ρ (in kg/m 3), having a weighted average hydraulic size ω, m/sec, according to formula (6) and on the mobility of sediment of size d captured in the pipe and dragged along the bottom, m, according to formula (7)

(6)

where V is the speed of water flow in gravity lines, m/sec;

u is the rate of precipitation of suspended particles in the flow; u≈0.07∙V m/sec;

D – diameter of gravity lines, m;

A – parameter taken equal to 7.5-10;

d – particle diameter, m.

The diameter of gravity water intake lines must ensure the possibility of hydraulic removal of sediment deposited in them.

Siphon pipes are allowed to be used in water intakes of categories II and III. These pipes, as previously noted, are made from welded steel pipes; their number is assumed to be at least two.

The diameter of the siphon pipes is determined by the flow rate during normal operation of the water intake and by the speed of water movement in them 0.7-1.2 m/sec.

The greatest amount of vacuum should be created at the top point of the siphon, at which an air collector connected to a vacuum pump is installed. The permissible height of the siphon, equal to the difference between the elevations of its top point and the low water level (LW), is determined in emergency mode using the formula:

where is the permissible vacuum at the highest point of the siphon, taken 0.6-0.7 mPa;

– pressure loss along the length of the siphon from the receiving point to the air collector, m;

∑ξ – the sum of the local resistance coefficients in the siphon;

V is the speed of water movement in the siphon conduit during emergency mode, m/sec;

h in – pressure loss in the ascending branch of the siphon, m.

Total pressure loss in the siphon line and water receiver:

h=h in +һ n +һ solve, m(9)

where h n – pressure loss along the length and local resistance of the siphon, m;

h solve – pressure loss in the grid, m.

Pressure loss in gratings 0.03-0.06 m.

The calculation is made for the conditions of normal and emergency operation of the water intake.

Businesses and homes consume large amounts of water. These digital indicators become not only evidence of a specific value indicating consumption.

In addition, they help determine the diameter of the pipe assortment. Many people believe that calculating water flow based on pipe diameter and pressure is impossible, since these concepts are completely unrelated.

But practice has shown that this is not so. The throughput capabilities of the water supply network depend on many indicators, and the first in this list will be the diameter of the pipe assortment and the pressure in the main.

It is recommended to calculate the pipe capacity depending on its diameter at the design stage of pipeline construction. The data obtained determines the key parameters of not only the home, but also the industrial highway. All this will be discussed further.

Calculate the pipe capacity using an online calculator

ATTENTION! To calculate correctly, you need to note that 1 kgf/cm2 = 1 atmosphere; 10 meters of water column = 1 kgf/cm2 = 1 atm; 5 meters of water column = 0.5 kgf/cm2 and = 0.5 atm, etc. Fractional numbers are entered into the online calculator through a dot (For example: 3.5 and not 3.5)

Enter parameters for calculation:

What factors influence the permeability of liquid through a pipeline?

The criteria that influence the described indicator make up a large list. Here are some of them.

The inner diameter that the pipeline has.
The speed of flow, which depends on the pressure in the line.
Material taken for the production of pipe assortment.

The water flow rate at the outlet of the main is determined by the diameter of the pipe, because this characteristic, together with others, affects the throughput of the system. Also, when calculating the amount of liquid consumed, one cannot discount the wall thickness, which is determined based on the expected internal pressure.

One could even argue that the definition of “pipe geometry” is not affected by the length of the network alone. And the cross section, pressure and other factors play a very important role.

In addition, some system parameters have an indirect rather than a direct effect on the flow rate. This includes the viscosity and temperature of the pumped medium.

To summarize, we can say that determining the throughput allows you to accurately determine the optimal type of material for building the system and make a choice of the technology used for its assembly. Otherwise, the network will not function efficiently and will require frequent emergency repairs.

Calculation of water consumption by diameter round pipe, depends on its size. Consequently, over a larger cross section, a significant amount of liquid will move within a certain period of time. But when performing calculations and taking into account the diameter, one cannot discount the pressure.

If we consider this calculation using a specific example, it turns out that less liquid will pass through a meter-long pipe product through a 1 cm hole over a certain time period than through a pipeline reaching a height of a couple of tens of meters. This is natural, because the highest level of water consumption on the site will reach the highest values at the maximum pressure in the network and at the highest values of its volume.

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Section calculations according to SNIP 2.04.01-85

First of all, you need to understand that calculating the diameter of a culvert is a complex engineering process. This will require special knowledge. But when carrying out the domestic construction of a culvert, hydraulic calculations of the cross-section are often carried out independently.

This type of design calculation of flow velocity for a culvert can be carried out in two ways. The first is tabular data. But, turning to the tables, you need to know not only the exact number of taps, but also containers for collecting water (baths, sinks) and other things.

Only if you have this information about the culvert system, you can use the tables provided by SNIP 2.04.01-85. They are used to determine the volume of water based on the girth of the pipe. Here is one such table:

External volume of pipe assortment (mm)

Approximate amount of water obtained in liters per minute

Approximate amount of water, calculated in m3 per hour

If you focus on SNIP standards, you can see the following in them - the daily volume of water consumed by one person does not exceed 60 liters. This is provided that the house is not equipped with running water, and in a situation with comfortable housing, this volume increases to 200 liters.

Clearly, these volume data showing consumption are interesting as information, but a pipeline specialist will need to determine completely different data - this is the volume (in mm) and the internal pressure in the line. This cannot always be found in the table. And formulas help you find out this information more accurately.

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It is already clear that the cross-sectional dimensions of the system affect the hydraulic calculation of consumption. For home calculations, a water flow formula is used, which helps to obtain the result given the pressure and diameter of the pipe product. Here is the formula:

Formula for calculation based on pressure and pipe diameter: q = π×d²/4 ×V

In the formula: q shows the water consumption. It is calculated in liters. d is the size of the pipe section, it is shown in centimeters. And V in the formula is a designation for the speed of movement of the flow, it is shown in meters per second.

If the water supply network is powered by a water tower, without the additional influence of a pressure pump, then the flow speed is approximately 0.7 - 1.9 m/s. If any pumping device is connected, then the passport for it contains information about the coefficient of pressure generated and the speed of movement of the water flow.

This formula is not the only one. There are many more. They can be easily found on the Internet.

In addition to the presented formula, it should be noted that the internal walls of pipe products have a huge impact on the functionality of the system. For example, plastic products have a smooth surface than their steel counterparts.

For these reasons, the resistance coefficient of plastic is significantly lower. Plus, these materials are not affected by corrosive formations, which also has a positive effect on the throughput of the water supply network.

Determination of head loss

The water passage is calculated not only by the diameter of the pipe, it is calculated by pressure drop. Losses can be calculated using special formulas. Which formulas to use, everyone will decide for themselves. To calculate the required values, you can use various options. There is no single universal solution to this issue.

But first of all, it is necessary to remember that the internal clearance of the passage of a plastic and metal-plastic structure will not change after twenty years of service. And the internal clearance of the passage of a metal structure will become smaller over time.

And this will entail the loss of some parameters. Accordingly, the speed of water in the pipe in such structures is different, because in some situations the diameter of the new and old network will be noticeably different. The resistance value in the line will also differ.

Also, before calculating the necessary parameters for the passage of liquid, you need to take into account that the loss of water supply flow velocity is associated with the number of turns, fittings, volume transitions, the presence of shut-off valves and friction force. Moreover, all this when calculating the flow rate must be carried out after careful preparation and measurements.

Calculating water consumption using simple methods is not easy. But, if you have the slightest difficulty, you can always turn to specialists for help or use an online calculator. Then you can count on the fact that the installed water supply or heating network will work with maximum efficiency.

Video - how to calculate water consumption

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Hydraulic calculations of free-flow (gravity) pipelines are based on the condition of maintaining the steady uniform movement of water in the pipes according to two basic formulas:

flow continuity formula

Chezy formula

where q is liquid flow, m 3 /s; ω—free section area, m2; V—fluid velocity, m/s; R—hydraulic radius, m; i is the hydraulic slope (equal to the slope of the pipe at steady uniform motion); C is the Chezy coefficient, depending on the hydraulic radius and the roughness of the wetted surface of the pipeline, m 0.5 / s.

The main difficulty in carrying out hydraulic calculations is determining the Chezy coefficient.

A number of researchers have proposed their own universal formulas (empirical or semi-empirical dependencies), which to one degree or another describe the dependence of the Chezy coefficient on the hydraulic radius, the roughness of the pipeline walls and other factors:

formula of N, N. Pavlovsky:

where n is the relative roughness of the pipe wall; to determine the exponent y, the formula is used

y=2.5·√n-0.13-0.75·√R·(√n-0.1)

A. Manning formula:

formula of A.D. Altshul and V.A. Ludov for determining y.

y=0.57-0.22 lgC

formula of A. A. Karpinsky:

y=0.29-0.0021·C.

On the basis of these and other similar dependencies, hydraulic calculation tables and nomograms have been constructed, which allow design engineers to carry out hydraulic calculations of gravity networks and channels made of various materials. It is recommended to calculate free-flow gravity pipelines using the well-known Darcy-Weisbach formula:

i=λ/4R V 2 /2g

where λ is the coefficient of hydraulic friction; g—gravitational acceleration, m/s 2 .

The Chezy coefficient can be defined as:

Of the previously noted formulas obtained by domestic researchers, the most tested and best consistent with experimental data are the formulas of N. N. Pavlovsky. The validity of these formulas has been confirmed and tested by engineering practice, and there is no doubt about the possibility of their further use for the hydraulic calculation of free-flow networks made of ceramics, concrete and brick, i.e. those materials where the roughness coefficient n is of the order of 0.013-0.014, as well as polymeric ones certain correction factors.

Current trends in the widespread use of new pipes made of various materials (including polymers) during the repair and reconstruction of old networks lead to the fact that the drainage network of cities becomes more and more heterogeneous from year to year, which affects the difficulties of assessing hydraulic indicators, as well as difficulty in operation, since appropriate maintenance methods (for example, cleaning, etc.) must be applied for each dissimilar section of the pipeline.

For pipelines made of new materials, there are currently no strict hydraulic dependencies for changes in coefficients C and λ. Moreover, each manufacturer of new types of pipes publishes its own, sometimes biased, criteria for assessing the hydraulic compatibility of pipes made of various materials. The task is even more aggravated when there are many such materials and each of them finds its niche when repairing networks. As a result, a kind of network with “patches” appears. This does not exclude hydraulic imbalance, i.e., possible negative trends associated with flooding at pipe junctions or at certain distances from junctions.

Thus, for each type of pipeline material or protective coating, it is desirable for the designer to have unified dependencies for changes in hydraulic characteristics, i.e., the results of full-scale experiments to determine the Chezy, Darcy coefficients and other parameters of pipes made of various materials. Hence, as a conclusion, it is necessary to state the importance of conducting experimental hydraulic studies. The experimental values of the Chezy coefficient obtained during experiments on one diameter can be a criterion for approximate hydraulic similarity for the transition to other diameters.

Calculation of the diameters of water intake communication pipelines is carried out based on the values of permissible velocities under normal operating conditions of the water intake. For gravity pipes, according to the speed should be in the range from 1 to 1.5. The diameter of gravity pipes is taken according to Shevelev’s tables.

We accept two gravity lines. We accept 700 mm =1.23 m/s.

Determination of losses in gravity lines arising during operation:

, Where

L is the length of the gravity line. The length of the gravity line is determined from the river bottom profile. This is the horizontal distance from the outer wall of the water intake (taken at a distance of 5 m from the water edge at the water level) to the location of the head, L = 43.5 m.

V – speed of water flow in the pipe,
=1.23 m/s;

=2.45 m/s;

 - the sum of local resistance coefficients, we take according to:

= exhausttank=

3*0,25+0,1+0,97+1,0=3.57m

Normal mode:

0.47 m

Emergency mode:

Q av. =Q calc =961.22l/s;

1.65 m

7. System for washing cassette filters, heads and gravity pipes

Fig.5. System for washing cassette filters, heads and gravity pipes.

When the level difference in the river and in one or both chambers of the well reaches a critical value, it is necessary to begin washing the filter cassettes and gravity pipes. The level difference is determined by sensor readings. First, the filters of one of the heads are pulsed washed. If after 3-4 pulse washings of filters and gravity pipelines, the level difference is not restored to normal values, then begin pressure backwashing. The pipelines supplying water for flushing of gravity lines and filters are connected in the switching chamber to the pressure water conduit. The diameter of the supply pipelines is determined as follows:

The water velocity during backwash must satisfy the following condition:

Where - water speed in the washing line, take 1.5 m/s;

- water speed in the gravity line, m/s

In this case, the water consumption for flushing the gravity line is determined by the formula:

Where - gravity line diameter, m

m/s

m 3 /s

According to the diameter of the wash water supply pipes, we accept
4m/s diameter
mm.

Pulse flushing calculation

Rice. 6. Calculation of pulse washing.

The calculation of pulse washing of fish protection cassettes of flooded water intakes consists of determining the maximum speed of water flow in a gravity water conduit during washing. Based on this speed, one can indirectly judge the effectiveness of its use (for example, in comparison with the possibly achievable flow speed when backwashing with water). The maximum speed of water flow in a gravity conduit
m/s, for some accepted values , L, D and d are determined by the formula

Where And - semi-amplitude of fluctuations in the liquid level in the vacuum riser, m;

, - duration of the first half-cycle of liquid level fluctuation in the vacuum riser

where F and ω are the areas of the live cross-section of the vacuum riser and gravity water conduit, respectively.
at F=ω

L-gravity line length

Ѳ- characteristic of the main hydraulic resistance is determined by the formula:

In this case, the coefficient ѱ is found using the formula:

Where, λ is the coefficient of hydraulic friction;

L and Dс - length and diameter of the gravity water conduit, m;

∑ζ - the sum of the coefficients of local resistance when water moves from the water source to inclusive.

h – pressure loss in the filter cassette, h = 0.3;

V is the speed of water in the filter cassette, determined by the formula:

,m/s

Where,
- speed of water flow into the cassette

Ρ=50% - cassette loading porosity

m/s

The characteristics of additional resistance are found using the formula

where D u d is the diameter of the vacuum riser and the air intake valve, respectively. D=700 mm;d=100 mm;

We define - height of water rise in the vacuum riser

accepted 3-8 m

Using the pulse washing calculation schedule, we determine

;
m/s

Determination of the diameters of gravity pipelines

Water from the head is transported through two gravity lines. The diameter of the gravity lines should be such that the speed of water movement along them is not less than the speed of water movement in the river in order to minimize the deposition of silt. To do this, during a flood with increased turbidity, we pass the entire flow through one gravity line, with a speed Vfav = 1.31 m/s.

The diameter of the gravity pipeline is determined by the formula:

dс.tr.=v(4*Qр/рV)=??4*0.4/3.14*1.31?=0.62m

we accept steel pipes with a diameter dс.tr = 700 mm, with a speed V = 0567 m/s, according to Shevelev’s table, during low-water periods the entire flow rate of 0.22 m/s will be passed through two gravity lines, with a speed V = 0.283 m/s, according to SNIP.

Pressure loss when water moves in gravity lines is determined by the formula:

??=i*?+?(zh*VI)/2g+?р, where

i - hydraulic slope or pressure loss per unit length of the pipeline (determined according to the Shevelev table),

Estimated length of the gravity pipeline, m,

g - resistance coefficient, taken depending on the local obstacle (determined from the reference book by A.N. Kurganov and N.F. Fedorov “Handbook for hydraulic calculations of water supply systems”).

For the case of shutting down one line for repair or flushing.

For the case of two lines operation.

As a result of calculating pressure losses, we determine the water level marks of the well. Let's use the following values:

For a narrowing transition - w=0.25

For two welded bends with an angle of 45° - w = 0.45

For a tee in the forward direction of the pipe - w=0.1

For a valve - w=50

To exit from the pipe (spout) into the water intake chamber - w=1

Therefore - ?f=51.8

Thus, we calculate the pressure loss when water moves along one gravity line:

Along the length i*?

This means that the pressure loss along the length will be equal to:

0.00061 *120m=0.0732

Pressure loss through the gratings?p=0.1 and the sum? is:

H=0.0732*51.8*(0.8І/2*9.81) +0.1=0.227

We found pressure losses when the entire water flow moves along one gravity line.

We determine the loss of water pressure when flow is passed through two gravity lines.

2) Along the length i*?

According to Shevelev’s tables for a flow rate of 800 mі/h.

Based on this flow rate, we determine it using Shevelev’s table:

d=700 mm, therefore, і=0.00061 (1000 і=0.61), with a speed V=0.567 m/s.

By consumption:

According to this flow rate, which we pass through two steel pipes with a diameter of 700 mm according to the Shevelev table, 1000 i = 0.178, therefore, i = 0.000178 with a speed V = 0.286 m/s, which means losses along the length:

??= i*?=0.00061 *120m=0.0732

Amount?f=51.8

H=51.8*0.4І/2*9.81+0.0732+0.1=0.596

We obtain pressure losses through two gravity pipelines.

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