What pipe diameter is needed depending on the flow rate and pressure. How to calculate water consumption based on pipe cross-section How to calculate water consumption based on pipe diameter
In some cases, you have to deal with the need to calculate the water flow through the pipe. This indicator indicates how much water the pipe can pass, measured in m³ / s.
- For organizations that have not supplied the water meter, the charge is based on the account of the pipe's patency. It is important to know how accurately these data are calculated, for what and at what rate you have to pay. This does not apply to individuals, for them, in the absence of a meter, the number of registered people is multiplied by the consumption of water by 1 person according to sanitary standards. This is a fairly large volume, and with modern tariffs it is much more profitable to supply a meter. In the same way, in our time, it is often more profitable to heat water yourself with a column than to pay utilities for their hot water.
- The calculation of the permeability of the pipe plays a huge role when designing a house, when connecting communications to the house .
It is important to make sure that each branch of the water supply will be able to get its share of the main pipe, even during peak flow times. The water supply system is designed for comfort, convenience, and ease of labor for a person.
If every evening the residents of the upper floors will practically not reach the water, what kind of comfort can we talk about? How can you drink tea, wash dishes, swim? And everyone drinks tea and bathes, so the amount of water that the pipe could provide was distributed over the lower floors. This problem can play a very bad role in firefighting. If firefighters connect to the central pipe, and there is no pressure in it.
Sometimes calculating the flow of water through a pipe can come in handy if, after repairing the water supply system by would-be masters, replacing part of the pipes, the pressure has dropped significantly.
Hydrodynamic calculations are not easy and are usually performed by qualified professionals. But let's say you are engaged in private construction, designing your cozy spacious house.
How to calculate the water flow through the pipe yourself?
It would seem that it is enough to know the diameter of the pipe hole in order to get, maybe, rounded, but generally fair figures. Alas, this is very little. Other factors can change the result of calculations at times. What affects the maximum water flow through the pipe?
- Pipe section... An obvious factor. The starting point for fluid dynamics calculations.
- Pipe pressure... With increasing pressure, more water passes through a pipe with the same cross section.
- Bends, turns, diameters, bifurcations inhibit the movement of water through the pipe. Different variants to varying degrees.
- Pipe length... Longer pipes will carry less water per unit of time than shorter ones. The whole secret is in the force of friction. Just as it delays the movement of objects familiar to us (cars, bicycles, sledges, etc.), the frictional force impedes the flow of water.
- A pipe with a smaller diameter turns out to have more area of contact of water with the surface of the pipe in relation to the volume of water flow. And from each point of contact, a friction force appears. Just as in longer pipes, in narrower pipes the speed of water movement becomes slower.
- Pipe material... Obviously, the degree of roughness of the material affects the magnitude of the friction force. Modern plastic materials (polypropylene, PVC, metal-plastic, etc.) are very slippery compared to traditional steel and allow water to move faster.
- Duration of pipe operation... Lime deposits, rust greatly impair the flow capacity of the water supply system. This is the most tricky factor, because the degree of pipe clogging, its new internal relief and friction coefficient are very difficult to calculate with mathematical precision. Fortunately, calculating water consumption is most often required for new construction and fresh, unused materials. On the other hand, this system will be connected to the existing communications that have been existing for many years. And how will she behave herself in 10, 20, 50 years? Newest technologies greatly improved this situation. Plastic pipes do not rust, their surface practically does not deteriorate over time.
Calculation of water flow through the tap
The volume of the outflowing liquid is found by multiplying the section of the pipe opening S by the outflow velocity V. The section is the area of a certain part of the volumetric figure, in this case, the area of a circle. Found by the formula S = πR2... R will be the radius of the pipe hole, not to be confused with the radius of the pipe. π is a constant, the ratio of the circumference of a circle to its diameter, approximately 3.14.
The outflow rate is found by the Torricelli formula:. Where g is the gravitational acceleration on planet Earth equal to approximately 9.8 m / s. h is the height of the water column above the hole.
Example
Let's calculate the water flow through a faucet with an opening with a diameter of 0.01 m and a column height of 10 m.
Hole section = πR2 = 3.14 x 0.012 = 3.14 x 0.0001 = 0.000314 m2.
Outflow velocity = √2gh = √2 x 9.8 x 10 = √196 = 14 m / s.
Water flow = SV = 0.000314 x 14 = 0.004396 m³ / s.
Translated into liters, it turns out that 4.396 liters per second can flow out of a given pipe.
Why do we need such calculations
When drawing up a plan for the construction of a large cottage with several bathrooms, a private hotel, organization fire system, it is very important to have more or less accurate information about the transporting 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 quite 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. "Passability of the pipe". In this case, the question of the tariffs applied in this case is quite logical.
It is important to understand that the second option does not apply to private premises (apartments and cottages), where, in the absence of meters, when calculating payment, sanitary standards are taken into account: usually it is up to 360 l / day per person.
What determines the permeability of the pipe
What determines the flow rate of water in a circular 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 will be able to pass in a certain time. And a simple formula for the volume of a pipe will allow you to find out this value. At the same time, the 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 factors affecting water consumption.
In addition to them, the following points must also be taken into account:
- 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, the water is influenced exclusively 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 high values.
- Water consumption depends on the diameter to a much more complex degree than it seems at first glance. When the pipe diameter is small, the walls resist water flow by an order of magnitude more than in thicker systems. As a result, as the diameter of the pipe decreases, its advantage in terms of the ratio of the flow rate to the internal area index in the fixed length section decreases. To put it simply, a thick water pipe transports water much faster than a thin one.
- Manufacturing material... Another important point, directly affecting the speed of movement of water through the pipe. For example, smooth propylene is much more conducive to water sliding than rough steel walls.
- Duration of service... Over time, rust appears on steel pipes. In addition, it is typical for steel, as well as for cast iron, to gradually accumulate lime deposits. The resistance to water flow of pipes with deposits is much higher than that of new steel products: this difference sometimes reaches 200 times. In addition, overgrowing 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 plastic and metal-plastic products do not have such problems: even after decades of intensive use, the level of their resistance to water flows remains at the original level.
- The presence of turns, fittings, adapters, valves contributes to additional inhibition 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. As a conclusion, we can say that a simple determination of the pipe diameter from the water flow rate is hardly possible.
New ability to calculate water consumption
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 outflow hole are much smaller than the diameter of the water supply system. In this case, the formula for calculating water over the cross section of the Torricelli pipe v ^ 2 = 2gh is applicable, where v is the speed of flow through a small hole, g is the acceleration of gravity, and h is the height of the water column above the tap (a hole with a cross section s, per unit time passes the 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 water column 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 extracting the square root, v = 13.98570698963767 comes out. After rounding off to get a simpler speed reading, the result is 14m / s. The cross-section of a 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 to carry out. Also in the public domain there are special tables indicating water consumption for the most popular sanitary ware, with a minimum value of 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 rate. However, you can still derive certain indicators for yourself. This is especially true if the system is equipped with plastic or metal-plastic pipes, and water consumption is carried out by taps with a small outlet section. In some cases, this method of calculation is applicable to steel systems, but we are talking primarily about new water pipelines, which did not have time to be covered with internal deposits on the walls.
Water consumption in a watercourse is the volume of liquid passing through the cross section. Consumable unit - m3 / s.
The calculation of the consumed water should be carried out even at the planning stage of the water supply system, since the main parameters of the water pipelines depend on this.
Water consumption in the pipeline: factors
In order to independently calculate the flow rate of water in the pipeline, you need to know the factors that ensure the permeability of water in the pipeline.
The main ones are the degree of pressure in the water conduit and the diameter of the pipe section. But, knowing only these values, it will not be possible to accurately calculate the water consumption, since it also depends on such indicators as:
- Pipe length. With this, everything is clear: the longer its length, the higher the degree of friction of the water against its walls, so the fluid flow slows down.
- The material of the pipe walls is also an important factor on which the flow rate depends. So, the smooth walls of a polypropylene pipe give the least resistance than steel.
- The diameter of the pipeline - the smaller it is, the higher the resistance of the walls to the movement of the liquid will be. The narrower the diameter, the more disadvantageous is the correspondence of the outer surface area to the inner volume.
- The service life of the water supply system. We know that over the years they are exposed to corrosion, and lime deposits form on cast iron. The frictional force against the walls of such a pipe will be significantly higher. For example, the surface resistance of a rusty pipe is 200 times higher than that of a new steel pipe. / Li>
- Changing the diameter at different sections of the conduit, bends, shut-off fittings or fittings significantly reduce the flow rate.
What are the quantities used to calculate the water flow rate?
The following values are used in the formulas:
- Q is the total (annual) water consumption per person.
- N is the number of residents of the house.
- Q is the daily flow rate.
- K - coefficient of uneven consumption, equal to 1.1-1.3 (SNiP 2.04.02-84).
- D is the pipe diameter.
- V is the water flow rate.
Formula for calculating water consumption
So, knowing the values, we get the following formula for water consumption:
- For daily calculation - Q = Q × N / 100
- For hourly calculation - q = Q × K / 24.
- Calculation by diameter - q = × d2 / 4 × V.
Example of calculating water consumption for a household consumer
The house has a toilet, washbasin, bathtub, kitchen sink.
- According to Appendix A, we take the flow rate per second:
- Toilet bowl - 0.1 l / sec.
- Washbasin with mixer - 0.12 l / sec.
- Bath - 0.25 l / sec.
- Kitchen sink - 0.12 l / sec.
- The sum of water consumed from all supply points will be:
- 0.1 + 0.12 + 0.25 + 0.12 = 0.59 l / s
- According to the total flow rate (Appendix B) 0.59 l / s corresponds to the design flow rate of 0.4 l / s.
You can convert to cubic meters per hour by multiplying it by 3.6. Thus, it turns out: 0.4 x 3.6 = 1.44 cubic meters / hour
Procedure for calculating water consumption
The entire calculation procedure is specified in the set of rules 30. 13330. 2012 SNiP 2.04.01-85 * "Internal water supply and sewerage" updated edition.
If you are planning to start building a house, redeveloping an apartment or installing plumbing structures, then information on how to calculate water consumption will be very useful .. Calculation of water consumption will help not only determine the required volume of water for a particular room, but will also allow you to timely identify a decrease in pressure in the pipeline. In addition, thanks to simple formulas, all this can be done independently, without resorting to the help of specialists.
When laying water mains, the most difficult thing is to calculate the throughput of pipe sections. Correct calculations will ensure that the water flow rate is not too large and its pressure does not decrease.
The importance of correct calculations
Calculation of water consumption allows you to choose the right material and pipe diameter
When designing a cottage with two or more bathrooms or a small hotel, it is necessary to take into account how much water the pipes of the selected section can supply. After all, if the pressure in the pipeline drops with a large consumption, this will lead to the fact that it will be impossible to take a shower or a bath normally. If a problem arises in a fire, you may even lose your home. Therefore, the calculation of the cross-country ability of highways is carried out even before the start of construction.
For small business owners, it is also important to know the throughput rates. Indeed, in the absence of metering devices, utilities, as a rule, present an invoice for water consumption to organizations according to the volume passed by the pipe. Knowing the data on your water supply will allow you to control water consumption and not pay extra.
What determines the permeability of the pipe
Water consumption will depend on the configuration of the water supply system, as well as the type of pipes from which the network is mounted
The permeability of pipe sections is a metric value that characterizes the volume of liquid passed through the pipeline for a certain time interval. This indicator depends on the material used in the manufacture of pipes.
Plastic pipelines maintain almost the same permeability throughout the entire operating period. Plastic, in comparison with metal, does not rust, thanks to this, the lines do not clog for a long time.
For metal models, the throughput decreases year after year. Due to the fact that pipes rust, the inner surface gradually flakes off and becomes rough. Because of this, much more plaque forms on the walls. In particular, hot water pipes clog up quickly.
In addition to the material of manufacture, the permeability also depends on other characteristics:
- The length of the plumbing. The greater the length, the lower the flow rate due to the influence of the friction force, and the pressure also decreases accordingly.
- Pipe diameter. The walls of narrow lines create more resistance. The smaller the cross-section, the worse the ratio of the flow rate to the value of the internal area in a section of a fixed length will be. In wider pipelines, water moves faster.
- The presence of bends, fittings, adapters, taps. Any fittings slow down the movement of water flows.
When determining the indicator bandwidth it is necessary to take into account all these factors in combination. In order not to get confused in numbers, it is worth using proven formulas and tables.
Calculation methods
The coefficient of friction is influenced by the presence of locking elements and their number
To determine the permeability of the water supply system, you can use three calculation methods:
The last method, although the most accurate, is not suitable for calculating ordinary household communications. It is quite complex, and for its application you will need to know a variety of indicators. To calculate a simple network for a private house, you should resort to using an online calculator. Although not as accurate, it is free and does not need to be installed on a computer. You can get more accurate information by comparing the data calculated by the program with the table.
How to calculate bandwidth
The tabular method is the simplest. Several tables of counting have been developed: you can choose the one that is suitable depending on the known parameters.
Calculation based on pipe section
In SNiP 2.04.01-85, it is proposed to find out the amount of water consumption by the pipe circumference.
In accordance with the SNiP standards, the daily water consumption by one person is no more than 60 liters. This data is for a house without running water. If a water supply network is installed, the volume increases to 200 liters.
Calculation based on the temperature of the coolant
As the temperature rises, the permeability of the pipe decreases - the water expands and thereby creates additional friction.
You can calculate the required data using a special table:
| Pipe section (mm) | Bandwidth | |||
| By heat (hl / h) | By heat carrier (t / h) | |||
| Water | Steam | Water | Steam | |
| 15 | 0,011 | 0,005 | 0,182 | 0,009 |
| 25 | 0,039 | 0,018 | 0,650 | 0,033 |
| 38 | 0,11 | 0,05 | 1,82 | 0,091 |
| 50 | 0,24 | 0,11 | 4,00 | 0,20 |
| 75 | 0,72 | 0,33 | 12,0 | 0,60 |
| 100 | 1,51 | 0,69 | 25,0 | 1,25 |
| 125 | 2,70 | 1,24 | 45,0 | 2,25 |
| 150 | 4,36 | 2,00 | 72,8 | 3,64 |
| 200 | 9,23 | 4,24 | 154 | 7,70 |
| 250 | 16,6 | 7,60 | 276 | 13,8 |
| 300 | 26,6 | 12,2 | 444 | 22,2 |
| 350 | 40,3 | 18,5 | 672 | 33,6 |
| 400 | 56,5 | 26,0 | 940 | 47,0 |
| 450 | 68,3 | 36,0 | 1310 | 65,5 |
| 500 | 103 | 47,4 | 1730 | 86,5 |
| 600 | 167 | 76,5 | 2780 | 139 |
| 700 | 250 | 115 | 4160 | 208 |
| 800 | 354 | 162 | 5900 | 295 |
| 900 | 633 | 291 | 10500 | 525 |
| 1000 | 1020 | 470 | 17100 | 855 |
To summarize plumbing system this information is not extremely important, but is considered the main indicator for heating circuits.
Searching data depending on pressure
The water flow pressure of the common line is taken into account when selecting pipes
When selecting pipes for the installation of any communication network, it is necessary to take into account the flow pressure in the common line. If there is a head under high pressure, it is necessary to install pipes with a larger cross-section than when moving by gravity. If these parameters are not taken into account when selecting pipe sections, and a large water flow is passed through small networks, they will make noise, vibrate and quickly become unusable.
To find the largest calculated water flow, a table of pipe throughput is used depending on the diameter and different indicators of water pressure:
| Consumption | Bandwidth | |||||||||
| Pipe section | 15 mm | 20 mm | 25 mm | 32 mm | 40 mm | 50 mm | 65 mm | 80 mm | 100 mm | |
| Pa / m | Mbar / m | Less than 0.15 m / s | 0.15 m / s | 0.3 m / s | ||||||
| 90,0 | 0,900 | 173 | 403 | 745 | 1627 | 2488 | 4716 | 9612 | 14940 | 30240 |
| 92,5 | 0,925 | 176 | 407 | 756 | 1652 | 2524 | 4788 | 9756 | 15156 | 30672 |
| 95,0 | 0,950 | 176 | 414 | 767 | 1678 | 2560 | 4860 | 9900 | 15372 | 31104 |
| 97,5 | 0,975 | 180 | 421 | 778 | 1699 | 2596 | 4932 | 10044 | 15552 | 31500 |
| 100,0 | 1000,0 | 184 | 425 | 788 | 1724 | 2632 | 5004 | 10152 | 15768 | 31932 |
| 120,0 | 1200,0 | 202 | 472 | 871 | 1897 | 2898 | 5508 | 11196 | 17352 | 35100 |
| 140,0 | 1400,0 | 220 | 511 | 943 | 2059 | 3143 | 5976 | 12132 | 18792 | 38160 |
| 160,0 | 1600,0 | 234 | 547 | 1015 | 2210 | 3373 | 6408 | 12996 | 20160 | 40680 |
| 180,0 | 1800,0 | 252 | 583 | 1080 | 2354 | 3589 | 6804 | 13824 | 21420 | 43200 |
| 200,0 | 2000,0 | 266 | 619 | 1151 | 2488 | 3780 | 7200 | 14580 | 22644 | 45720 |
| 220,0 | 2200,0 | 281 | 652 | 1202 | 2617 | 3996 | 7560 | 15336 | 23760 | 47880 |
| 240,0 | 2400,0 | 288 | 680 | 1256 | 2740 | 4176 | 7920 | 16056 | 24876 | 50400 |
| 260,0 | 2600,0 | 306 | 713 | 1310 | 2855 | 4356 | 8244 | 16740 | 25920 | 52200 |
| 280,0 | 2800,0 | 317 | 742 | 1364 | 2970 | 4356 | 8568 | 17338 | 26928 | 54360 |
| 300,0 | 3000, | 331 | 767 | 1415 | 3078 | 4680 | 8892 | 18000 | 27900 | 56160 |
The average pressure in most of the risers varies from 1.5 to 2.5 atmospheres. The dependence on the number of floors is regulated by dividing the water supply network into several branches. Water injection by means of pumps also affects the change in flow rate.
Also, when calculating the water flow through the pipe according to the table of pipe diameter and pressure values, not only the number of taps is taken into account, but also the number of water heaters, bathtubs and other consumers.
Hydraulic calculation according to Shevelev
For the most accurate identification of the indicators of the entire water supply network, special reference materials are used. They define the running characteristics for pipes made of different materials.
Why do we need such calculations
When drawing up a plan for the construction of a large cottage with several bathrooms, a private hotel, organization of a fire system, it is very important to have more or less accurate information about the transporting 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 quite 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. "Passability of the pipe". In this case, the question of the tariffs applied in this case is quite logical.
It is important to understand that the second option does not apply to private premises (apartments and cottages), where, in the absence of meters, when calculating payment, sanitary standards are taken into account: usually it is up to 360 l / day per person.
What determines the permeability of the pipe
What determines the flow rate of water in a circular 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 will be able to pass in a certain time. At the same time, the 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 factors affecting water consumption.
In addition to them, the following points must also be taken into account:
- 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, the water is influenced exclusively 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 high values.
- Water consumption depends on the diameter to a much more complex degree than it seems at first glance. When the pipe diameter is small, the walls resist water flow by an order of magnitude more than in thicker systems. As a result, as the diameter of the pipe decreases, its advantage in terms of the ratio of the flow rate to the internal area index in the fixed length section decreases. To put it simply, a thick water pipe transports water much faster than a thin one.
- Manufacturing material... Another important point that directly affects the speed of water movement through the pipe. For example, smooth propylene is much more conducive to water sliding than rough steel walls.
- Duration of service... Over time, rust appears on steel pipes. In addition, it is typical for steel, as well as for cast iron, to gradually accumulate lime deposits. The resistance to water flow of pipes with deposits is much higher than that of new steel products: this difference sometimes reaches 200 times. In addition, overgrowing 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 plastic and metal-plastic products do not have such problems: even after decades of intensive use, the level of their resistance to water flows remains at the original level.
- The presence of turns, fittings, adapters, valves contributes to additional inhibition 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. As a conclusion, we can say that a simple determination of the pipe diameter from the water flow rate is hardly possible.
New ability to calculate water consumption
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 outflow hole are much smaller than the diameter of the water supply system. In this case, the formula for calculating water over the cross section of the Torricelli pipe v ^ 2 = 2gh is applicable, where v is the speed of flow through a small hole, g is the acceleration of gravity, and h is the height of the water column above the tap (a hole with a cross section s, per unit time passes the 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 water column 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 extracting the square root, v = 13.98570698963767 comes out. After rounding off to get a simpler speed reading, the result is 14m / s. The cross-section of a 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 to carry out. Also in the public domain there are special tables indicating water consumption for the most popular sanitary ware, with a minimum value of 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 rate. However, you can still derive certain indicators for yourself. This is especially true if the system is equipped with plastic or metal-plastic pipes, and water consumption is carried out by taps with a small outlet section. In some cases, this method of calculation is applicable to steel systems, but we are talking primarily about new water pipelines, which did not have time to be covered with internal deposits on the walls.
Water consumption by pipe diameter: determining the diameter of the pipeline depending on the flow rate, calculation by section, the formula for the maximum flow rate at pressure in a circular pipe
Water consumption by pipe diameter: determining the diameter of the pipeline depending on the flow rate, calculation by section, the formula for the maximum flow rate at pressure in a circular pipe
Water flow through a pipe: is a simple calculation possible?
Is any simple calculation of the water flow rate based on the pipe diameter possible? Or the only way is to contact specialists, having previously depicted detailed map all the water pipes in the area?
After all, hydrodynamic calculations are extremely difficult ...
Our task is to find out how much water this pipe can pass.
What is it for?
- When self-calculating plumbing systems.
If you plan to build big house with several guest baths, a mini - hotel, think over a fire extinguishing system - it is advisable to know how much water a pipe of a given diameter can supply at a certain pressure.
After all, a significant drop in pressure at the peaks of water consumption is unlikely to please the residents. And a weak trickle of water from a fire hose is likely to be useless.
- In the absence of water meters, utilities typically invoice organizations “by pipe passability”.
Please note: the second scenario does not affect apartments and private houses. If there are no water meters, utility bills charge for water in accordance with sanitary standards. For modern well-maintained houses, this is no more than 360 liters per person per day.
We must admit: a water meter greatly simplifies relations with utilities
Factors affecting the permeability of the pipe
What affects the maximum water flow rate in a circular pipe?
The obvious answer
Common sense dictates that the answer should be very simple. There is a water pipe. There is a hole in it. The more it is, the more water will pass through it per unit of time. Oh, sorry, more pressure.
Obviously, a 10 centimeter column of water will push less water through a centimeter hole than a water column as high as a ten-story building.
So, from the inner section of the pipe and from the pressure in the water supply system, right?
Do you really need something else?
Correct answer
No. These factors affect the expense, but they are just the beginning of a long list. Calculating the flow rate of water by the diameter of the pipe and the pressure in it is like calculating the trajectory of a rocket flying to the moon, based on the apparent position of our satellite.
If we do not take into account the rotation of the Earth, the movement of the Moon in its own orbit, the resistance of the atmosphere and the gravity of celestial bodies, our spacecraft is unlikely to get even approximately to the desired point in space.
How much water will pour out of a pipe with a diameter x at a pressure in the path y is influenced not only by these two factors, but also by:
- Pipe length... The longer it is, the stronger the friction of water against the walls slows down the flow of water in it. Yes, the water at the very end of the pipe is affected only by the pressure in it, but the next volumes of water should take its place. And the water pipe slows them down, and how.
It is because of the loss of pressure in a long pipe that pumping stations are installed on oil pipelines.
- The diameter of the pipe affects the water flow much more difficult than common sense suggests... For small diameter pipes, the wall resistance to flow is much greater than for thick pipes.
The reason is that the smaller the pipe, the less favorable it is in terms of water flow rate, the ratio of the internal volume and surface area at a fixed length.
Simply put, it is easier for water to move through a thick pipe than through a thin one.
- Wall material is another important factor on which the speed of water movement depends.... If water slides over smooth polypropylene, like the sirloin of a clumsy lady on the sidewalk in ice, then rough steel creates much more resistance to flow.
- The age of the pipe also greatly affects the permeability of the pipe.... Steel water pipes rust, in addition, steel and cast iron over the years of operation are overgrown with lime deposits.
The overgrown pipe has much greater resistance to flow (resistance to polished new steel pipe and rusty differ 200 times!). Moreover, the areas inside the pipe, due to overgrowth, reduce their lumen; even under ideal conditions, much less water will pass through the overgrown pipe.
Do you think it makes sense to calculate the permeability along the pipe diameter at the flange?
Please note: the surface condition of plastic and metal-polymer pipes does not deteriorate over time. After 20 years, the pipe will have the same resistance to the flow of water as at the time of installation.
- Finally, any turn, change in diameter, a variety of valves and fittings - all this also slows down the flow of water.
Oh, if the above factors could be neglected! However, we are not talking about deviations within the margin of error, but about the difference in times.
All this leads us to a sad conclusion: a simple calculation of the water flow through the pipe is impossible.
A ray of light in the dark realm
In the case of a water flow through a tap, however, the task can be drastically simplified. The main condition for a simple calculation: the hole through which water is poured out must be negligible compared to the diameter of the water supply pipe.
Then Torricelli's law applies: v ^ 2 = 2gh, where v is the outflow velocity from the small hole, g is the acceleration of gravity, and h is the height of the water column that stands above the hole. In this case, the volume of liquid s * v will pass through the hole with the cross section s per unit time.
The master left you a gift
Do not forget: the section of the hole is not the diameter, it is the area equal to pi * r ^ 2.
For a water column of 10 meters (which corresponds to an excess pressure of one atmosphere) and a hole with a diameter of 0.01 meters, the calculation will be as follows:
We take the square root and get v = 13.98570698963767. For simplicity of calculations, we will round the value of the flow velocity to 14 m / s.
The section of a hole with a diameter of 0.01 m is 3.14159265 * 0.01 ^ 2 = 0.000314159265 m2.
Thus, the water flow through our hole will be equal to 0.000314159265 * 14 = 0.00439822971 m3 / s, or slightly less than four and a half liters per second.
As you can see, in this variant, the calculation is not very complicated.
In addition, in the appendix to the article, you will find a table of water consumption by the most common plumbing fixtures, indicating the minimum diameter of the connection.
Conclusion
That's all, in short. As you can see, universal simple solution We have not found; however, hopefully you find this article helpful. Good luck!
How to calculate the throughput of a pipe
Calculation of throughput is one of the most difficult tasks when laying a pipeline. In this article we will try to figure out exactly how this is done for different types pipelines and pipe materials.
High capacity pipes
Carrying capacity is an important parameter for any pipes, canals and other heirs of the Roman aqueduct. However, the throughput is not always indicated on the pipe packaging (or on the product itself). In addition, how much fluid the pipe passes through the section also depends on the pipeline diagram. How to correctly calculate the throughput of pipelines?
Methods for calculating the throughput of pipelines
There are several methods for calculating this parameter, each of which is suitable for a particular case. Some designations that are important in determining the throughput of a pipe:
Outside diameter - the physical size of the pipe section from one edge of the outer wall to the other. In calculations, it is designated as Dn or Dн. This parameter is indicated in the marking.
Nominal bore is an approximate value of the diameter of the internal section of the pipe, rounded to the nearest whole number. In calculations, it is designated as Du or Du.
Physical methods for calculating the throughput of pipes
The values of the throughput of pipes are determined by special formulas. For each type of product - for gas, water supply, sewerage - the calculation methods are different.
Tabular calculation methods
There is a table of approximate values created to facilitate the determination of the throughput of pipes for intra-apartment wiring. In most cases, high precision is not required, so values can be applied without complex calculations. But this table does not take into account the decrease in throughput due to the appearance of sediment build-up inside the pipe, which is typical for old highways.
There is an accurate flow rate calculation table, called the Shevelev table, which takes into account the pipe material and many other factors. These tables are rarely used when laying a water supply system around an apartment, but in a private house with several non-standard risers they can come in handy.
Calculation using programs
At the disposal of modern plumbing firms there are special computer programs for calculating the throughput of pipes, as well as many other similar parameters. In addition, online calculators have been developed that, although less accurate, are free and do not require installation on a PC. One of the stationary programs "TAScope" is a creation of Western engineers, which is shareware. IN large companies use "Hydrosystem" - a domestic program that calculates pipes according to criteria that affect their operation in the regions of the Russian Federation. In addition to hydraulic calculation, it allows you to read other parameters of pipelines. The average price is 150,000 rubles.
How to calculate the throughput of a gas pipe
Gas is one of the most difficult materials to transport, in particular because it has the property of being compressed and therefore able to escape through the smallest gaps in pipes. To the calculation of the throughput of gas pipes (as well as to the design gas system in general) have special requirements.
The formula for calculating the throughput of a gas pipe
The maximum throughput of gas pipelines is determined by the formula:
Qmax = 0.67 Du2 * p
where p is equal to the operating pressure in the gas pipeline system + 0.10 MPa or the absolute gas pressure;
Du - nominal pipe bore.
Exist complex formula for calculating the throughput of a gas pipe. When carrying out preliminary calculations, as well as when calculating a domestic gas pipeline, it is usually not used.
Qmax = 196.386 Du2 * p / z * T
where z is the coefficient of compressibility;
T is the temperature of the transported gas, K;
According to this formula, the direct dependence of the temperature of the transported medium on the pressure is determined. The higher the T value, the more the gas expands and pushes against the walls. Therefore, when calculating large pipelines, engineers take into account possible weather conditions in the area where the pipeline passes. If the nominal value of the pipe DN is less than the gas pressure generated when high temperatures in summer (for example, at + 38 ... + 45 degrees Celsius), then damage to the highway is likely. This entails the leakage of valuable raw materials, and creates the possibility of an explosion of the pipe section.
Table of flow rates of gas pipes depending on pressure
There is a table for calculating the throughput of a gas pipeline for commonly used pipe diameters and nominal working pressure. To determine the characteristics of a gas pipeline of non-standard dimensions and pressure, engineering calculations will be required. Also, the pressure, speed and volume of gas are influenced by the temperature of the outside air.
The maximum speed (W) of the gas in the table is 25 m / s, and the z (coefficient of compressibility) is 1. The temperature (T) is 20 degrees Celsius or 293 Kelvin.
Sewer pipe throughput
Bandwidth sewer pipe- an important parameter that depends on the type of pipeline (pressure or gravity). The calculation formula is based on the laws of hydraulics. In addition to the laborious calculation, tables are used to determine the throughput of the sewage system.
Hydraulic calculation formula
For the hydraulic calculation of the sewage system, it is required to determine the unknowns:
- pipeline diameter DN;
- average flow velocity v;
- hydraulic slope l;
- the degree of filling h / Du (in the calculations, they are repelled by the hydraulic radius, which is associated with this value).
In practice, they are limited to calculating the value of l or h / d, since the rest of the parameters are easy to calculate. In preliminary calculations, the hydraulic slope is considered to be equal to the slope of the earth's surface, at which the movement Wastewater will not be lower than self-cleaning speed. The speed values as well as the maximum h / DN values for domestic networks can be found in table 3.
In addition, there is a standardized value for the minimum slope for pipes with a small diameter: 150 mm
(i = 0.008) and 200 (i = 0.007) mm.
The formula for the volumetric flow rate of liquid looks like this:
where a is the flow area,
v - flow velocity, m / s.
The speed is calculated using the formula:
where R is the hydraulic radius;
C is the wetting coefficient;
From here, you can derive the formula for the hydraulic slope:
According to it, this parameter is determined if a calculation is required.
where n is the roughness factor, ranging from 0.012 to 0.015, depending on the pipe material.
The hydraulic radius is considered equal to the normal radius, but only when the pipe is completely filled. In other cases, use the formula:
where A is the cross-flow area of the fluid,
P is the wetted perimeter, or the transverse length of the inner surface of the pipe that touches the liquid.
Tables of throughput of gravity sewer pipes
The table includes all the parameters used to perform the hydraulic calculation. The data is selected by the value of the pipe diameter and substituted into the formula. Here, the volumetric flow rate of the liquid q passing through the cross-section of the pipe has already been calculated, which can be taken as the throughput of the line.
In addition, there are more detailed tables of the Lukins, containing ready-made values of throughput for pipes of different diameters from 50 to 2000 mm.
Tables of throughput of pressure head sewage systems
In the tables of the capacity of the pressure pipes of the sewage system, the values depend on the maximum degree of filling and the calculated average flow rate of the waste water.
Water pipe throughput
Plumbing pipes are most commonly used in the home. And since they are under heavy load, then the calculation of the throughput of the water main becomes important condition reliable operation.
Permeability of the pipe depending on the diameter
Diameter is not the most important parameter when calculating the permeability of a pipe, but it also affects its value. The larger the inner diameter of the pipe, the higher the permeability, as well as the lower the chance of blockages and plugs. However, in addition to the diameter, it is necessary to take into account the coefficient of friction of water against the pipe walls (tabular value for each material), the length of the pipeline and the difference in fluid pressures at the inlet and outlet. In addition, the number of elbows and fittings in the pipeline will greatly affect permeability.
Table of throughput of pipes by temperature of the coolant
The higher the temperature in the pipe, the lower its throughput, since the water expands and thereby creates additional friction. This is not important for the water supply system, but in heating systems is a key parameter.
There is a table for calculations for heat and coolant.
Table of throughput of pipes depending on the pressure of the coolant
There is a table describing the capacity of pipes depending on the pressure.
Table of pipe throughput depending on diameter (according to Shevelev)
F.A. and A.F.Shevelev's tables are one of the most accurate tabular methods for calculating the throughput of a water supply system. In addition, they contain all the necessary calculation formulas for each specific material. This is a voluminous informative material used most often by hydraulic engineers.
The tables take into account:
- pipe diameters - inner and outer;
- wall thickness;
- service life of the water supply system;
- line length;
- the purpose of pipes.
Pipe throughput depending on diameter, pressure: tables, calculation formulas, online calculator
Calculation of throughput is one of the most difficult tasks when laying a pipeline. In this article we will try to figure out exactly how this is done for different types of pipelines and pipe materials.