Businesses, as well as apartments and houses in general, consume large amounts of water. The numbers are huge, but can they say anything else, except for the fact of a certain expense? Yes they can. Namely, the water flow can help calculate the diameter of the pipe. It would seem that these parameters are not related to each other, but in fact the relationship is obvious.

After all, the throughput of the water supply system depends on many factors. A significant place in this list is precisely the diameter of the pipes, as well as the pressure in the system. Let's delve deeper into this issue.

Factors affecting the permeability of water through a pipe

The flow rate of water through a circular pipe with a hole depends on the size of this hole. Thus, the larger it is, the more water will pass through the pipe in a certain period of time. However, do not forget about pressure. After all, you can give an example. A meter pillar will push water through a centimeter hole much less per unit time than a pillar with a height of several tens of meters. It is obvious. Therefore, the water flow will reach its maximum at the maximum internal section of the product, as well as at the maximum pressure.

Diameter calculation

If you need to get a certain water flow at the outlet of the water supply system, then you can not do without calculating the diameter of the pipe. After all, this indicator, along with the rest, affects the throughput rate.

Of course, there are special tables that are on the Web and in specialized literature that allow you to bypass the calculations, focusing on certain parameters. However, one should not expect high accuracy from such data, the error will still be present, even if all factors are taken into account. Therefore, the best way to obtain accurate results is to independently calculate.

For this you will need the following data:

• Water consumption consumption.
• Head loss from the starting point to the point of consumption.

It is not necessary to calculate the consumption of water consumption - there is a digital standard. You can take data on the mixer, which says that about 0.25 liters are consumed per second. This figure can be used for calculations.

An important parameter for obtaining accurate data is the head loss in the area. As you know, the head pressure in standard water supply risers is in the range from 1 to 0.6 atmospheres. The average is 1.5-3 atm. The parameter depends on the number of floors in the house. But this does not mean that the higher the house, the higher the pressure in the system. In very tall buildings (more than 16 floors), a division of the system into floors is sometimes used to normalize the pressure.

With regard to head loss, this figure can be calculated using pressure gauges at the starting point and before the point of consumption.

If, nevertheless, knowledge and patience for self-calculation is not enough, then you can use tabular data. And let them have certain errors, the data will be accurate enough for certain conditions. And then, according to the water consumption, it will be very easy and quick to get the diameter of the pipe. This means that the water supply system will be calculated correctly, which will make it possible to obtain such an amount of liquid that will satisfy the needs.

Working with the calculator is simple - enter data and get the result. But sometimes this is not enough - an accurate calculation of the pipe diameter is possible only with manual calculation using formulas and correctly selected coefficients. How to calculate the diameter of the pipe according to the water flow? How to determine the size of the gas line?

When calculating the required pipe diameter, professional engineers most often use special programs that can calculate and give an accurate result using known parameters. It is much more difficult for an amateur builder to perform the calculation on his own to organize water supply, heating, gasification systems. Therefore, most often, when building or reconstructing a private house, the recommended pipe sizes are used. But not always standard advice can take into account all the nuances of individual construction, so you need to manually perform a hydraulic calculation in order to choose the right pipe diameter for heating and water supply.

Calculation of pipe diameter for water supply and heating

The main criterion for selecting a heating pipe is its diameter. From this indicator depends on how effective the heating of the house will be, the life of the system as a whole. With a small diameter in the lines, increased pressure can occur, which will cause leaks, increased stress on pipes and metal, which will lead to problems and endless repairs. With a large diameter, the heat transfer of the heating system will tend to zero, and cold water will simply ooze from the tap.

pipe capacity

The diameter of the pipe directly affects the throughput of the system, that is, in this case, the amount of water or coolant passing through the section per unit time matters. The more cycles (movements) in the system for a certain period of time, the more efficient the heating. For water supply pipes, the diameter affects the initial water pressure - a suitable size will only maintain pressure, and an enlarged one will reduce it.

According to the diameter, a plumbing and heating scheme is selected, the number of radiators and their sectionality, and the optimal length of the mains is determined.

Since the throughput of the pipe is a fundamental factor when choosing, you should decide what, in turn, affects the permeability of water in the line.

Factors influencing the patency of the highway:

1. The pressure of water or coolant.
2. The inner diameter (section) of the pipe.
3. The total length of the system.
4. pipeline material.
5. Pipe wall thickness.

On the old system, the patency of the pipe is aggravated by lime, silt deposits, the effects of corrosion (on metal products). All this together reduces the amount of water passing through the section over time, that is, used lines work worse than new ones.

It is noteworthy that this indicator does not change for polymer pipes - plastic is much less than metal, allowing slag to accumulate on the walls. Therefore, the throughput of PVC pipes remains the same as on the day they were installed.

Calculation of pipe diameter by water flow

Determining the right amount of water

To determine the diameter of the pipe by the flow rate of the passing liquid, you will need the values ​​​​of the true water consumption, taking into account all plumbing fixtures: a bathtub, a kitchen faucet, a washing machine, a toilet bowl. Each individual section of the water supply system is calculated according to the formula:

qc = 5× q0 × α, l/s

where qc is the value of water consumed by each device;

q0 is a normalized value, which is determined by SNiP. We accept for the bath - 0.25, for the kitchen faucet 0.12, for the toilet bowl -0.1;

a is a coefficient that takes into account the possibility of simultaneous operation of plumbing fixtures in the room. Depends on the probability value and the number of consumers.

In sections of the highway where the water flows for the kitchen and the bath, for the toilet and the bath, etc., are combined, the probability value is added to the formula. That is, the possibility of simultaneous operation of a kitchen faucet, bathroom faucet, toilet bowl and other appliances.

The probability is determined by the formula:

Р = qhr µ × u/q0 × 3600 × N,

where N is the number of water consumers (devices);

qhr µ is the maximum hourly water consumption that can be taken according to SNiP. We choose for cold water qhr µ = 5.6 l / s, the total flow is 15.6 l / s;

u is the number of people using plumbing.

Example of water consumption calculation:

The two-storey house has 1 bathroom, 1 kitchen with installed washing machine and dishwasher, shower, 1 toilet. A family of 5 lives in the house. Calculation algorithm:

1. We calculate the probability P = 5.6 × 5 / 0.25 × 3600 × 6 = 0.00518.
2. Then the water flow for the bathroom will be qc = 5 × 0.25 × 0.00518=0.006475 l/s.
3. For the kitchen qc \u003d 5 × 0.12 × 0.00518 \u003d 0.0031 l / s.
4. For a toilet, qc = 5× 0.1 × 0.00518=0.00259 l/s.

We calculate the diameter of the pipe

There is a direct dependence of the diameter on the volume of the flowing liquid, which is expressed by the formula:

where Q is water consumption, m3/s;

d – pipeline diameter, m;

w is the flow velocity, m/s.

By transforming the formula, we can select the value of the diameter of the pipeline, which will correspond to the volume of water consumed:

Yulia Petrichenko, expert

d = √(4Q/πw), m

The flow rate of water can be taken from Table 2. There is a more complex method for calculating the flow rate - taking into account losses and the coefficient of hydraulic friction. This is a rather voluminous calculation, but in the end it allows you to get the exact value, unlike the tabular method.

Example: Calculate the diameter of the pipe for the bathroom, kitchen and toilet, based on the obtained water flow rates. We select from table 2 the value of the water flow rate in the pressure water supply - 3 m / s.

Why do we need such calculations

When drawing up a plan for the construction of a large cottage with several bathrooms, a private hotel, the organization of a fire system, it is very important to have more or less accurate information about the transport capabilities of the existing pipe, taking into account its diameter and pressure in the system. It's all about pressure fluctuations during the peak of water consumption: such phenomena seriously affect the quality of the services provided.

In addition, if the water supply system is not equipped with water meters, then when paying for utility services, the so-called. "Permeability of the pipe". In this case, the question of the tariffs applied in this case quite logically emerges.

At the same time, it is important to understand that the second option does not apply to private premises (apartments and cottages), where, in the absence of meters, sanitary standards are taken into account when calculating payment: usually this is up to 360 l / day per person.

What determines the permeability of the pipe

What determines the flow of water in a round pipe? One gets the impression that the search for an answer should not cause difficulties: the larger the cross section of the pipe, the greater the volume of water it can pass in a certain time. A simple formula for the volume of the pipe will allow you to find out this value. At the same time, pressure is also remembered, because the higher the water column, the faster the water will be forced through the communication. However, practice shows that these are far from all the factors affecting water consumption.

In addition to them, the following points also have to be taken into account:

1. Pipe length. With an increase in its length, the water rubs against its walls more strongly, which leads to a slowdown in the flow. Indeed, at the very beginning of the system, water is only affected by pressure, but it is also important how quickly the next portions will have the opportunity to enter the communication. Braking inside the pipe often reaches large values.
2. Water consumption depends on the diameter to a much more complex extent than it seems at first glance. When the size of the pipe diameter is small, the walls resist the water flow by an order of magnitude more than in thicker systems. As a result, as the diameter of the pipe decreases, its benefit in terms of the ratio of the water flow rate to the indicator of the internal area in a section of a fixed length decreases. To put it simply, a thick plumbing system transports water much faster than a thin one.
3. Production material. Another important point that directly affects the speed of movement of water through the pipe. For example, smooth propylene promotes water sliding to a much greater extent than rough steel walls.
4. Service life. Over time, rust appears on steel water pipes. In addition, for steel, as well as for cast iron, it is typical to gradually accumulate lime deposits. The resistance to water flow of a pipe with deposits is much higher than that of new steel products: this difference sometimes reaches 200 times. In addition, the overgrowth of the pipe leads to a decrease in its diameter: even if we do not take into account the increased friction, its permeability clearly decreases. It is also important to note that products made of plastic and metal-plastic do not have such problems: even after decades of intensive use, their level of resistance to water flows remains at the original level.
5. The presence of turns, fittings, adapters, valves contributes to additional braking of water flows.

All of the above factors have to be taken into account, because we are not talking about some small errors, but about a serious difference several times over. As a conclusion, it can be said that a simple determination of the pipe diameter from the water flow is hardly possible.

New possibility of water consumption calculations

If the use of water is carried out by means of a tap, this greatly simplifies the task. The main thing in this case is that the dimensions of the hole for the outpouring of water are much smaller than the diameter of the water pipe. In this case, the formula for calculating water over the cross section of the Torricelli pipe v ^ 2 \u003d 2gh is applicable, where v is the speed of flow through a small hole, g is the acceleration of free fall, and h is the height of the water column above the tap (a hole having a cross section s, per unit time passes water volume s*v). It is important to remember that the term "section" is used not to denote the diameter, but its area. To calculate it, use the formula pi * r ^ 2.

If the column of water has a height of 10 meters and the hole has a diameter of 0.01 m, the water flow through the pipe at a pressure of one atmosphere is calculated as follows: v^2=2*9.78*10=195.6. After taking the square root, v=13.98570698963767. After rounding to get a simpler speed figure, the result is 14m/s. The cross section of the hole, having a diameter of 0.01 m, is calculated as follows: 3.14159265*0.01^2=0.000314159265 m2. As a result, it turns out that the maximum water flow through the pipe corresponds to 0.000314159265 * 14 = 0.00439822971 m3 / s (slightly less than 4.5 liters of water / second). As you can see, in this case, the calculation of water over the cross section of the pipe is quite simple. Also freely available are special tables indicating the water consumption for the most popular plumbing products, with a minimum value for the diameter of the water pipe.

As you can already understand, there is no universal simple way to calculate the diameter of the pipeline depending on the water flow. However, you can still deduce certain indicators for yourself. This is especially true in cases where the system is equipped with plastic or metal-plastic pipes, and water is consumed by taps with a small outlet cross section. In some cases, this calculation method is applicable to steel systems, but we are talking primarily about new water pipes that have not had time to become covered with internal deposits on the walls.

The calculation of water consumption is made before the construction of pipelines and is an integral part of hydrodynamic calculations. During the construction of main and industrial pipelines, these calculations are made using special programs. When building a domestic pipeline with your own hands, you can carry out the calculation yourself, but it should be borne in mind that the result obtained will not be as accurate as possible. How to calculate the water consumption parameter, read on.

Factors Affecting Throughput

The main factor by which the pipeline system is calculated is the throughput. This indicator is influenced by many different parameters, the most significant of which are:

1. pressure in the existing pipeline (in the main network, if the pipeline under construction will be connected to an external source). The calculation method taking into account pressure is more complex, but also more accurate, since it is pressure that determines such an indicator as throughput, that is, the ability to pass a certain amount of water in a certain unit of time;
2. the total length of the pipeline. The larger this parameter, the greater the number of losses manifested during its use and, accordingly, to eliminate the pressure drop, it is required to use pipes of a larger diameter. Therefore, this factor is also taken into account by specialists;
3. the material from which the pipes are made. If metal pipes are used for a structure or other line, then an uneven inner surface and the possibility of gradual clogging with deposits contained in the water will lead to a decrease in throughput and, accordingly, a slight increase in diameter. When using plastic pipes (PVC), polypropylene pipes, and so, the possibility of clogging with deposits is practically excluded. What's more, the inner surface of plastic pipes is smoother;

1. section of pipes. According to the internal section of the pipe, you can independently make a preliminary calculation.

There are other factors that experts take into account. But for this article they are not essential.

Method for calculating the diameter depending on the cross section of pipes

If, when calculating the pipeline, it is necessary to take into account all of these factors, it is recommended to make calculations using special programs. If preliminary calculations are sufficient for the construction of the system, then they are carried out in the following sequence:

• preliminary determination of the amount of water consumption by all family members;
• calculation of the optimal size of the diameter.

How to calculate the water consumption in the house

You can determine the amount of cold or hot water consumed in the house by several methods:

• according to the meter reading. If meters are installed when entering the pipeline into the house, then determining the water consumption per day per person is not a problem. Moreover, when observing for several days, you can get fairly accurate parameters;

• according to the established norms, determined by experts. The standard for water consumption per person is set for certain types of premises with the presence / absence of certain conditions;

• according to the formula.

To determine the total amount of water consumed in the room, it is necessary to make a calculation for each plumbing unit (bath, shower, faucet, and so on) separately. Calculation formula:

Qs \u003d 5 x q0 x P, where

Qs is an indicator that determines the amount of flow;

q0 is the established norm;

P is a coefficient that takes into account the possibility of using several types of plumbing fixtures at the same time.

The q0 indicator is determined depending on the type of plumbing equipment according to the following table:

The probability P is determined by the following formula:

P = L x N1 / q0 x 3600 x N2, where

L - peak water consumption for 1 hour;

N1 - the number of people using plumbing fixtures;

q0 - established standards for a separate plumbing unit;

N2 - the number of installed plumbing fixtures.

It is unacceptable to determine the water flow without taking into account the probability, since the simultaneous use of plumbing fixtures leads to an increase in the flow power.

Let's calculate water using a specific example. It is necessary to determine the water flow according to the following parameters:

• 5 people live in the house;
• 6 units of sanitary equipment are installed: a bathtub, a toilet bowl, a sink in the kitchen, a washing machine and a dishwasher installed in the kitchen, a shower cabin;
• peak water consumption for 1 hour in accordance with SNiP is set equal to 5.6 l / s.

Determine the size of the probability:

P \u003d 5.6 x 4 / 0.25 x 3600 x 6 \u003d 0.00415

We determine the consumption of oxen for the bath, kitchen and toilet room:

Qs (baths) = 4 x 0.25 x 0.00518 = 0.00415 (l/s)

Qs (kitchens) \u003d 4 x 0.12 x 0.00518 \u003d 0.002 (l / s)

Qs (toilet) \u003d 4 x 0.4 x 0.00518 \u003d 0.00664 (l / s)

Calculation of the optimal section

The following formula is used to determine the cross section:

Q \u003d (πd² / 4) xW, where

Q is the amount of water consumed calculated by calculation;

d is the desired diameter;

W is the speed of water movement in the system.

By simple mathematical operations, it can be deduced that

d = √(4Q/πW)

W can be obtained from the table:

The indicators presented in the table are used for approximate calculations. To obtain more accurate parameters, a complex mathematical formula is used.

Let's determine the diameter of the pipes for the bath, kitchen and toilet according to the parameters presented in this example:

d (for the bathroom) \u003d √ (4 x 0.00415 / (3.14 x 3)) \u003d 0.042 (m)

d (for the kitchen) \u003d √ (4 x 0.002 / (3.14 x 3)) \u003d 0.03 (m)

d (toilet) = √(4 x 0.00664 / (3.14 x 3)) = 0.053 (m)

To determine the cross section of pipes, the highest design indicator is taken. Given the small margin in this example, it is possible to conduct water supply with pipes with a cross section of 55 mm.

How to calculate using a special semi-professional program, see the video.

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Pipe capacity: simple about the complex

How does the throughput of a pipe vary with diameter? What factors, besides the cross section, affect this parameter? Finally, how to calculate, albeit approximately, the permeability of a water supply system with a known diameter? In the 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 it needed

Hydraulic calculation allows you to get the optimal minimum the diameter of the pipeline.

On the one hand, there is always a catastrophic shortage of money during construction and repair, and the price of a linear meter of pipes grows non-linearly with an increase in diameter. On the other hand, an underestimated section of the water supply will lead to an excessive drop in pressure at the end devices due to its hydraulic resistance.

With a flow rate 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 dramatically. 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 tasks under consideration to the plumbing 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 specialty - plumbing;
2. In the case of a large building with numerous plumbing fixtures, for the hydraulic calculation of the water supply system, it will be necessary to calculate the probability of using several water points at the same time. In a small house, the calculation is performed for peak demand by all available appliances, which greatly simplifies the task.

Factors

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

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

In real conditions (when designing a water supply system), the second task is much more often necessary.

Household logic suggests that the maximum flow of water 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 slows down due to friction against the walls. Moreover, the material and condition of the walls predictably affect the degree of braking.

Here is a complete list of factors that affect the performance of a water pipe:

• Pressure at the beginning of the water supply (read - pressure in the route);
• bias 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 the roughness, but also reduce the internal clearance of the pipeline;

This does not apply to glass, plastic, copper, galvanized and metal-polymer pipes. They are in like new condition even after 50 years of operation. An exception is the silting of the water supply with a large amount of suspensions and the absence of filters at the inlet.

• Quantity and Angle turns;
• Diameter changes plumbing;
• Presence or absence welds, soldering beads and connecting fittings;

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

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

Law of Torricelli

Evangelista Torricelli, who lived in the early 17th century, is known as a student of Galileo Galilei and the author of the very concept of atmospheric pressure. He also owns a formula describing the flow rate of water pouring out of a vessel through an opening of known dimensions.

For the Torricelli formula to work, it is necessary:

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

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

1. For the hole to be significantly smaller than the diameter of the vessel, thus eliminating the loss of pressure due to friction against the walls.

In practice, Torricelli's formula allows you to calculate the flow of water through a pipe with an internal section of known dimensions at a known instantaneous head during flow. Simply put: to use the formula, you need to install a pressure gauge in front of the tap or calculate the pressure drop on the water supply 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 orifice, in meters per second;
• g is the acceleration of fall (for our planet it is equal to 9.78 m/s^2);
• h - head (height of the water column above the hole).

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

Captain Evidence suggests: knowing the cross-sectional area, it is easy to determine the inner radius of the pipe. As you know, the area of ​​a circle is calculated as π*r^2, where π is rounded 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 stream flows. Converting the diameter to SI units (meters), we get 3.14159265*0.01^2=0.0003141593. And now we calculate the water flow: 20 * 0.0003141593 \u003d 0.006283186, or 6.2 liters per second.

Back to reality

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

Usually, the calculation problem is solved from the opposite: with known water flow through 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 flow rate for internal water pipes is considered to be 0.7 - 1.5 m / s. Exceeding the latter value leads to the appearance of hydraulic noise (primarily at bends and fittings).

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

The table shows data for mixers with aerators. Their absence equalizes the flow through the sink, washbasin and shower faucets with the flow through the faucet when taking a bath.

Let me remind you that if you want to calculate the water supply of a private house with your own hands, sum up the water consumption for all installed appliances. If this instruction is not followed, surprises will await you, such as a sharp drop in the temperature in the shower when you open the hot water tap on.

If there is a fire water supply in the building, 2.5 l / s for each hydrant is added to the planned flow. For fire water supply, the flow velocity is limited to 3 m/s: in case of fire, hydraulic noise is the last thing that will unnerve the residents.

When calculating the pressure, it is usually assumed that on the device extreme from the input it must be at least 5 meters, which corresponds to a pressure of 0.5 kgf / cm2. Some plumbing fixtures (flowing water heaters, filling valves of automatic 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 the hydraulic losses on the device itself.

In the photo - instantaneous water heater Atmor Basic. It includes heating only at a pressure of 0.3 kgf/cm2 and above.

Flow rate, diameter, speed

Let me remind you that they are linked to each other by two formulas:

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

Where can I get the values ​​for the radius of the inner section?

• For steel pipes, it is, with a minimum error, equal to half of the control(conditional pass, which is marked pipe rolling);
• For polymer, metal-polymer, etc. the inner diameter is equal to the difference between the outer one, with which the pipes are marked, and twice the wall thickness (it is also usually present in the marking). The radius, respectively, is half the inner diameter.

1. The inner diameter is 50-3 * 2 = 44 mm, or 0.044 meters;
2. The radius will be 0.044/2=0.022 meters;
3. The area of ​​​​the internal section will be equal to 3.1415 * 0.022 ^ 2 \u003d 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.

head loss

How to calculate how much pressure is lost on a water supply system 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 cherished pressure drop in meters;
• i - hydraulic slope of the water pipe meter;
• L is the length of the water supply in meters;
• K- coefficient, which makes it possible to simplify the calculation of the pressure drop on the stop 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 roulette yet.

The 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 1000i values ​​(hydraulic slope per 1000 meters of water supply) can be found in Shevelev's tables, which, in fact, serve for hydraulic calculation. The tables are too large for an article, as they give 1000i values ​​for all possible diameters, flow rates, and life-adjusted materials.

Here is a small fragment of the Shevelev table for a 25 mm plastic pipe.

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

Let's use this table to calculate the pressure drop on a 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. With a flow velocity as close as possible to 1.5 m/s (1.38 m/s), the value of 1000i will be equal to 142.8 meters;
2. The hydraulic slope of one meter of pipe will be equal to 142.8 / 1000 \u003d 0.1428 meters;
3. The correction factor for domestic water pipes 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 at 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 the 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 through a water supply system with known characteristics, one can select in the “flow rate” column of the complete Shevelev table such a value at which the pressure at the end of the pipe does not fall below 0.5 atmospheres.

Conclusion

Dear reader, if the above instructions, despite the extreme simplification, still seemed 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 will be grateful for your additions, corrections and comments. Good luck, comrades!

If you want to express gratitude, add a clarification or objection, ask the author something - add a comment or say thanks!