At enterprises, as well as in apartments and houses in general, it is spent a large number of water. The numbers are huge, but can they say anything more than the fact of a certain expense? Yes they can. Namely, the water flow rate can help to calculate the pipe diameter. These are seemingly unrelated parameters, 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 just the diameter of the pipes, as well as the pressure in the system. Let's take a deeper look at this issue.

Factors affecting the permeability of water through the 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, don't forget about pressure. After all, you can give an example. A meter pillar will push water through a centimeter hole much less per unit of time than a pillar with a height of several tens of meters. It is obvious. Therefore, the water consumption 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 flow rate of water at the outlet of the water supply system, then you cannot do without calculating the diameter of the pipe. After all, this indicator, along with the others, has an impact on the throughput indicator.

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 get accurate results is to calculate yourself.

To do this, you need the following data:

• Consumption of water consumption.
• Head loss from the starting point to the consumption point.

The consumption of water does not have to be calculated - there is a digital standard. You can take the 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 indicator 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 a very high houses(more than 16 floors) sometimes the system is divided into floors 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 although they have certain errors, the data will be accurate enough for certain conditions. And then, according to the water flow rate, it will be very simple and quick to obtain the diameter of the pipe. This means that the water supply system will be calculated correctly, which will allow you to get such an amount of liquid that will satisfy your needs.

Method for calculating Shevelev's table theoretical hydraulics SNiP 2.04.02-84

Initial data

Piping material: New steel without internal protective coating or with bitumen protective coating New cast iron without an inner protective coating or with a bituminous protective coating Non-new steel and cast iron without an inner protective coating or with a bituminous protective coating plastic or polymer-cement coating, applied by centrifugation Steel and cast iron, with an internal cement-sand coating, sprayed Steel and cast iron, with an internal cement-sand coating, applied by centrifugation From polymer materials(plastic) Glass

Estimated consumption

L / s m3 / hour

Outside diameter mm

Wall thickness mm

Pipeline length m

Average water temperature ° C

Equiv. roughness int. pipe surfaces: Heavily rusted or with large deposits Steel or cast iron old rusted Steel zinc plated. after several years Steel after several years Cast iron new Steel galvanized new Steel welded new Steel seamless new Drawn from brass, lead, copper Glass

Sum of local resistances

Payment

Pressure loss versus pipe diameter

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When calculating a water supply or heating system, you are faced with the task of selecting the diameter of the pipeline. To solve such a problem, you need to make a hydraulic calculation of your system, and for even more simple solution- you can use hydraulic calculation online, which we will now do.
Operating procedure:
1. Select the appropriate calculation method (calculation according to Shevelev tables, theoretical hydraulics or SNiP 2.04.02-84)
2. Select piping material
3. Set the calculated water flow rate in the pipeline
4. Set outside diameter and pipeline wall thickness
5. Set the length of the piping
6. Set average temperature water
The result of the calculation will be a graph and the values ​​of the hydraulic calculation given below.
The graph consists of two values ​​(1 - water pressure loss, 2 - water speed). Optimal values pipe diameter will be written in green below the graph.

Those. you must set the diameter so that the point on the graph is exactly above your green values ​​for the pipeline diameter, because only with such values, the water speed and head loss will be optimal.

The pressure loss in the pipeline indicates the pressure loss in a given section of the pipeline. The higher the losses, the more work will have to be done to deliver the water to the right place.
The characteristic of the hydraulic resistance shows how effectively the pipe diameter is selected depending on the pressure loss.
For reference:
- if you need to know the speed of a liquid / air / gas in a pipeline of various cross-sections - use

In this section, we will apply the law of conservation of energy to the movement of a liquid or gas through pipes. The movement of liquid through pipes is often found in technology and everyday life. Water is supplied through water pipes in the city to houses, to places of its consumption. In machines, oil for lubrication is supplied through pipes, fuel for engines, etc. The movement of fluid through pipes is often found in nature. Suffice it to say that the blood circulation of animals and humans is the flow of blood through tubes - blood vessels. To some extent, the flow of water in rivers is also a kind of fluid flow through pipes. The river bed is a kind of pipe for flowing water.

As you know, a stationary liquid in a vessel, according to Pascal's law, transfers external pressure in all directions and to all points of the volume without change. However, when the fluid flows without friction through a pipe, the cross-sectional area of ​​which is different in different sections, the pressure is not the same along the pipe. Let us find out why the pressure in a moving fluid depends on the cross-sectional area of ​​the pipe. But first, let's get acquainted with one important feature any fluid flow.

Suppose that the liquid flows through a horizontally located pipe, the cross-section of which is different in different places, for example, through a pipe, part of which is shown in Figure 207.

If we mentally draw several sections along the pipe, the areas of which are respectively equal and measure the amount of liquid flowing through each of them for a certain period of time, then we would find that the same amount of liquid has flowed through each section. This means that all the liquid that passes through the first section during the time passes through the third section in the same time, although it is much smaller in area than the first. If this were not the case and, for example, less liquid passed through the cross-section with an area over time than through the cross-section with an area, then the excess of liquid would have to accumulate somewhere. But the liquid fills the entire pipe, and there is nowhere for it to accumulate.

How can a liquid that has flowed through a wide section have time to "squeeze" through a narrow section in the same time? Obviously, for this, when passing through narrow parts of the pipe, the speed of movement must be greater, and just as many times as the cross-sectional area is smaller.

Indeed, consider a certain section of a moving liquid column, which coincides at the initial moment of time with one of the pipe sections (Fig. 208). Over time, this area will move to a distance that is equal to where is the velocity of the fluid flow. The volume V of the liquid flowing through the pipe section is equal to the product of the area of ​​this section by the length

In a unit of time, the volume of liquid flows -

The volume of fluid flowing per unit of time through the pipe section is equal to the product of the pipe cross-sectional area and the flow velocity.

As we have just seen, this volume should be the same in different sections of the pipe. Therefore, the smaller the cross-section of the pipe, the greater the speed of movement.

How much liquid passes through one section of the pipe in some time, the same amount of it must pass in such a

the same time through any other section.

At the same time, we believe that a given mass of liquid always has the same volume, that it cannot compress and reduce its volume (a liquid is said to be incompressible). It is well known, for example, that in narrow places of a river the speed of water flow is greater than in wide ones. If we denote the speed of fluid flow in sections by areas through then we can write:

From this it can be seen that when the liquid passes from the section of the pipe with larger area section into a section with a smaller sectional area, the flow velocity increases, i.e., the fluid moves with acceleration. And this, according to Newton's second law, means that a force acts on the fluid. What is this power?

This force can only be the difference between the pressure forces in the wide and narrow sections of the pipe. Thus, in a wide section, the fluid pressure must be greater than in a narrow section of the pipe.

The same follows from the law of conservation of energy. Indeed, if the velocity of the liquid increases in the narrow places of the pipe, then its kinetic energy also increases. And since we assumed that the fluid flows without friction, then this increase in kinetic energy must be compensated for by a decrease in potential energy, because the total energy must remain constant. What kind of potential energy are we talking about here? If the pipe is horizontal, then the potential energy of interaction with the Earth in all parts of the pipe is the same and cannot change. This means that only potential energy remains elastic interaction... The pressure force that causes the fluid to flow through the pipe is the elastic compressive force of the fluid. When we say that a liquid is incompressible, we only mean that it cannot be compressed enough to noticeably change its volume, but very small compression, which causes the appearance of elastic forces, inevitably occurs. These forces create fluid pressure. It is this compression of the liquid that decreases in the narrow parts of the pipe, compensating for the increase in speed. In narrow places of pipes, the fluid pressure must therefore be less than in wide ones.

This is the law discovered by St. Petersburg academician Daniel Bernoulli:

The pressure of the flowing fluid is greater in those sections of the flow in which the speed of its movement is less, and,

on the contrary, in those sections in which the velocity is higher, the pressure is lower.

Strange as it may seem, but when the liquid "squeezes" through narrow areas pipe, then its compression does not increase, but decreases. And experience confirms this well.

If the pipe through which the liquid flows is equipped with open pipes - manometers (fig. 209) - soldered into it, then it will be possible to observe the pressure distribution along the pipe. In narrow places of the pipe, the height of the liquid column in the manometric pipe is less than in wide ones. This means that there is less pressure in these places. The smaller the cross-section of the pipe, the higher the flow velocity in it and the lower the pressure. Obviously, it is possible to choose a section in which the pressure is equal to the external atmospheric pressure (the height of the liquid level in the manometer will then be equal to zero). And if we take an even smaller section, then the pressure of the liquid in it will be less than atmospheric.

This fluid flow can be used to evacuate air. The so-called water jet pump operates on this principle. Figure 210 shows a diagram of such a pump. A stream of water is passed through tube A with a narrow opening at the end. The water pressure at the pipe opening is less than atmospheric. That's why

gas from the evacuated volume is drawn through pipe B to the end of pipe A and removed together with water.

Everything that has been said about the movement of liquid through pipes also applies to the movement of gas. If the gas flow rate is not too high and the gas is not compressed enough to change its volume, and if, in addition, friction is neglected, then Bernoulli's law is also true for gas flows. In narrow parts of pipes, where the gas moves faster, its pressure is less than in wide parts, and may become less than atmospheric. In some cases, this doesn't even require a pipe.

A simple experiment can be done. If you blow on a sheet of paper along its surface, as shown in Figure 211, you can see that the paper will begin to rise up. This is due to the decrease in pressure in the air stream over the paper.

The same phenomenon occurs when an airplane is flying. The counter flow of air runs onto the convex upper surface of the wing of a flying aircraft, and due to this, the pressure decreases. The pressure above the wing is less than the pressure under the wing. This is why wing lift arises.

Exercise # 62

1. The permissible speed of oil flow through the pipes is 2 m / s. What volume of oil passes through a pipe with a diameter of 1 m in 1 hour?

2. Measure the amount of water flowing out of water tap for a certain time Determine the speed of the water flow by measuring the diameter of the pipe in front of the tap.

3. What should be the diameter of the pipeline through which the water should flow per hour? Allowable speed of water flow 2.5 m / sec.

The movement of fluid through pipes.
Dependence of fluid pressure on its flow rate

Stationary fluid flow. Continuity equation

Let us consider the case when an inviscid fluid flows through a horizontal cylindrical pipe with a varying cross-section.

The fluid flow is called stationary if at each point of the space occupied by the liquid, its velocity does not change over time. In a stationary flow, equal volumes of liquid are transferred through any cross-section of the pipe for equal periods of time.

Liquids practically incompressible, that is, we can assume that a given mass of liquid always has a constant volume. Therefore, the same volume of liquid passing through different sections pipe means that the flow rate of the fluid depends on the section of the pipe.

Let the velocities of the stationary fluid flow through the pipe sections S1 and S2 be equal to v1 and v2, respectively. The volume of the liquid flowing through the section S1 during the time interval t is equal to V1 = S1v1t, and the volume of the liquid flowing through the section S2 during the same time is equal to V2 = S2v2t. It follows from the equality V1 = V2 that

Relation (1) is called continuity equation... It follows from it that

Hence, for a steady flow of liquid, the velocities of motion of its particles through different cross-sections of the pipe are inversely proportional to the areas of these cross-sections.

Pressure in a moving fluid. Bernoulli's law

An increase in the flow rate of a liquid when moving from a pipe section with a larger cross-sectional area to a pipe section with a smaller cross-sectional area means that the fluid is moving with acceleration.

According to Newton's second law, force is the cause of acceleration. With this power in this case is the difference between the pressure forces acting on the flowing fluid in the wide and narrow parts of the pipe. Therefore, in the wide part of the pipe, the fluid pressure should be greater than in the narrow one. This can be directly observed in experience. In fig. it is shown that in sections of different cross-sections S1 and S2, manometric tubes are inserted into the pipe through which the liquid flows.

As observations show, the liquid level in the manometric tube at the section S1 of the pipe is higher than at the section S2. Consequently, the pressure in the liquid flowing through the section with the larger area S1 is higher than the pressure in the liquid flowing through the section with the smaller area S2. Hence, with a steady flow of liquid in those places where the flow velocity is lower, the pressure in the liquid is higher, and, conversely, where the flow velocity is higher, the pressure in the liquid is lower. Bernoulli first came to this conclusion, therefore this law is called Bernoulli law.

Disassembly of problem solving:

OBJECTIVE 1. Water flows in a horizontally positioned variable cross-section pipe. The flow velocity in the wide part of the pipe is 20 cm / s. Determine the speed of water flow in the narrow part of the pipe, the diameter of which is 1.5 times less than the diameter of the wide part.

OBJECTIVE 2. In a horizontally located pipe with a cross section of 20 cm2, a liquid flows. In one place, the pipe has a narrowing with a cross section of 12 cm2. The difference in liquid levels in the manometric tubes installed in the wide and narrow parts of the pipe is 8 cm. Determine the volumetric flow rate of the liquid in 1 s.

OBJECTIVE 3. A force of 15 N is applied to the horizontal syringe piston. Determine the rate of water flow from the syringe tip if the piston area is 12 cm2.

Pipes connecting various devices of chemical plants. With the help of them, substances are transferred between individual devices. Typically, several individual pipes use connections to create a single piping system.

A pipeline is a system of pipes connected together by connecting elements used for transportation chemical substances and other materials. In chemical plants, closed pipelines are usually used to move substances. When it comes to closed and insulated parts of the installation, then they also apply to the pipeline system or network.

A closed pipeline system may include:

1. Pipes.
2. Pipe fittings.
3. Sealing seals connecting two split pipeline sections.

All of the above elements are manufactured separately, after which they are connected into a single pipeline system. In addition, pipelines can be equipped with heating and the necessary insulation made of various materials.

The selection of the size of pipes and materials for production is carried out on the basis of technological and design requirements presented on a case-by-case basis. But for the standardization of pipe sizes, their classification and unification was carried out. The main criterion was the permissible pressure at which the pipe can be operated.

Nominal size DN

Nominal diameter DN (nominal diameter) is a parameter that is used in pipeline systems as a characterizing feature, with the help of which the fitting of pipeline parts, such as pipes, valves, fittings, and others, occurs.

The nominal diameter is a dimensionless quantity, however, it is numerically approximately equal to the inner diameter of the pipe. Example of nominal size designation: DN 125.

Also, the conditional passage is not indicated in the drawings and does not replace the actual pipe diameters. It roughly corresponds to the clear diameter at certain parts of the pipeline (fig. 1.1). If we talk about the numerical values ​​of the conditional transitions, then they are chosen in such a way that the throughput of the pipeline increases in the range from 60 to 100% during the transition from one conditional passage to the next.

Common nominal diameters:

3, 4, 5, 6, 8, 10, 15, 20, 25, 32, 40, 50, 65, 80, 100, 125, 150, 200, 250, 300, 350, 400, 450, 500, 600, 700, 800, 900, 1000, 1200, 1400, 1600, 1800, 2000, 2200, 2600, 2800, 3000, 3200, 3400, 3600, 3800, 4000.

The dimensions of these nominal passages are set so that there are no problems with the fit of parts to each other. Determination of the nominal diameter based on the value of the internal diameter of the pipeline, the nominal size is selected that is closest to the clear diameter of the pipe.

Nominal pressure PN

Nominal pressure PN is a value corresponding to the maximum pressure of the pumped medium at 20 ° C, at which a long-term operation of a pipeline with specified dimensions is possible.

Nominal pressure is dimensionless.

Like the nominal diameter, the nominal pressure has been calibrated based on operating experience gained from operating experience (Table 1.1).

The nominal pressure for a specific pipeline is selected based on the actual pressure created in it, by choosing the nearest higher value. In this case, fittings and valves in this pipeline must also correspond to the same pressure stage. The wall thickness of the pipe is calculated based on the nominal pressure and must ensure the operability of the pipe at a pressure value equal to the nominal (Table 1.1).

Permissible overpressure p e, zul

The pressure rating is only used for working temperature 20 ° C. As the temperature rises, the load capacity of the pipe decreases. Along with this, the permissible overpressure... The value of p e, zul shows the maximum overpressure that can be in the pipeline system with an increase in the operating temperature (Fig. 1.2).

Materials for pipelines

When choosing the materials that will be used for the manufacture of pipelines, indicators such as the characteristics of the medium that will be transported through the pipeline and operating pressure assumed in this system. It is also worth considering the possibility of corrosive effects from the pumped medium on the material of the pipe walls.

Almost all piping systems and chemical plants are manufactured from steel. For general use in the absence of high mechanical loads and corrosive action, gray cast iron or unalloyed structural steels are used for pipeline production.

For higher working pressures and no corrosive loads, a tempered steel or cast steel pipeline is used.

If the corrosive effect of the medium is high or high requirements are imposed on the purity of the product, then the pipeline is made of stainless steel.

If the pipeline must be resistant to impact sea ​​water, then copper-nickel alloys are used for its manufacture. Can also be applied aluminum alloys and metals such as tantalum or zirconium.

More and more widespread as a pipeline material are different kinds plastics, which is due to their high corrosion resistance, low weight and ease of processing. This material is suitable for waste water pipelines.

Shaped parts of the pipeline

Pipes made of plastic materials suitable for welding are assembled on site. These materials include steel, aluminum, thermoplastics, copper, etc. To connect straight pipe sections, specially made fittings are used, for example, elbows, bends, gates and diameter reductions (Fig. 1.3). These fittings can be part of any pipeline.

Pipe connections

To mount separate parts special connections are used for piping and fittings. They are also used to connect the necessary fittings and devices to the pipeline.

Connections are selected (fig. 1.4) depending on:

1. materials that are used for the manufacture of pipes and fittings. The main selection criterion is the ability to weld.
2. working conditions: low or high pressure, as well as low or high temperature.
3. production requirements that apply to the pipeline system.
4. the presence of detachable or permanent connections in the pipeline system.

Rice. 1.4 Types of pipe connections

Linear expansion of pipes and its complete set

The geometric shape of objects can be changed both by forceful action on them and by changing their temperature. Data physical phenomena lead to the fact that the pipeline, which is installed in an unloaded state and without temperature exposure, during operation under pressure or exposure to temperatures undergoes some linear expansion or contraction, which negatively affects its performance.

In the case when it is not possible to compensate for the expansion, deformation of the pipeline system occurs. This can damage the flange seals and those pipe joints.

Thermal linear expansion

When laying out pipelines, it is important to take into account the possible change in length as a result of temperature rise or the so-called thermal linear expansion, denoted by ΔL. This value depends on the length of the pipe, which is denoted by Lo and the temperature difference Δϑ = ϑ2-ϑ1 (Fig. 1.5).

In the above formula, a is the coefficient of thermal linear expansion of this material... This indicator is equal to the linear expansion of a 1 m long pipe with a temperature rise of 1 ° C.

Expansion compensation elements

Pipe bends

Thanks to special bends that are welded into the pipeline, the natural linear expansion of the pipes can be compensated. For this, compensating U-shaped, Z-shaped and angled bends, as well as lyre compensators are used (Fig. 1.6).

Rice. 1.6 Compensating pipe bends

They perceive the linear expansion of the pipes due to their own deformation. However, this method is only possible with some restrictions. In pipelines with high pressure knees are used at different angles to compensate for expansion. Due to the pressure that acts in such taps, increased corrosion is possible.

Corrugated pipe expansion joints

This device consists of a thin-walled metal corrugated pipe, which is called a bellows and stretches in the direction of the pipeline (fig. 1.7).

These devices are installed in the pipeline. The preload is used as a special expansion joint.

If we talk about axial expansion joints, then they are able to compensate only those linear expansions that occur along the pipe axis. An inner guide ring is used to avoid lateral movement and internal contamination. In order to protect the pipeline from external damage, as a rule, a special lining is used. Expansion joints that do not contain an inner guide ring absorb lateral movement as well as vibration that can come from the pumps.

Insulation of pipes

In the event that a medium with a high temperature moves through the pipeline, it must be insulated to avoid heat loss. In the case of a low-temperature environment moving through a pipeline, insulation is used to prevent it from heating up by the external environment. Insulation in such cases is carried out using special insulating materials that are placed around the pipes.

As such materials, as a rule, are used:

1. At low temperatures up to 100 ° C rigid foams such as polystyrene or polyurethane are used.
2. At average temperatures of around 600 ° C, shaped casings or mineral fibers such as stone wool or glass felt are used.
3. At high temperatures around 1200 ° C - ceramic fiber, such as alumina.

Pipes with a nominal diameter below DN 80 and an insulation layer thickness of less than 50 mm are usually insulated with insulating fittings. To do this, two shells are placed around the pipe and fastened together. metal tape, and then closed with a tin cover (Fig. 1.8).

Pipelines with a nominal bore greater than DN 80 must be provided with thermal insulation with a lower frame (Fig. 1.9). This frame consists of clamping rings, spacers and a metal cladding made of galvanized mild steel or stainless steel sheet. The space between the pipeline and the metal casing is filled with insulating material.

The thickness of the insulation is calculated by determining the costs of its manufacture, as well as losses that arise due to heat loss, and ranges from 50 to 250 mm.

Thermal insulation must be applied along the entire length of the piping system, including the bend and elbow areas. It is very important to take care not to create unprotected places that can cause heat loss. Flange connections and fittings must be supplied with shaped insulating elements (Fig. 1.10). This ensures unimpeded access to the connection point without the need to remove the insulating material from the entire piping system in the event that a leak has occurred.

In the event that the insulation of the pipeline system is chosen correctly, many tasks are solved, such as:

1. Avoiding a large drop in temperature in the flowing medium and, as a result, saving energy.
2. Preventing the temperature drop in gas pipelines below the dew point. Thus, it is possible to exclude the formation of condensation, which can lead to significant corrosion damage.
3. Avoid condensation in steam lines.