Heating systems must be tested for pressure resistance

From this article you will learn what static and dynamic pressure of a heating system is, why it is needed and how it differs. The reasons for its increase and decrease and methods for eliminating them will also be considered. In addition, we will talk about what kind of pressure they experience various systems heating and methods for this check.

Types of pressure in the heating system

There are two types:

• statistical;
• dynamic.

What's happened static pressure heating systems? This is what is created under the influence of gravity. Water under its own weight presses on the walls of the system with a force proportional to the height to which it rises. From 10 meters this figure is equal to 1 atmosphere. In statistical systems, flow blowers are not used, and the coolant circulates through pipes and radiators by gravity. These are open systems. The maximum pressure in an open heating system is about 1.5 atmospheres. IN modern construction such methods are practically not used, even when installing autonomous circuits country houses. This is due to the fact that for such a circulation scheme it is necessary to use pipes with a large diameter. It is not aesthetically pleasing and expensive.

The dynamic pressure in the heating system can be adjusted

Dynamic pressure in a closed heating system is created by artificially increasing the flow rate of the coolant using an electric pump. For example, if we are talking about high-rise buildings or large highways. Although, now even in private homes, pumps are used when installing heating.

Important! It's about about excess pressure without taking into account atmospheric pressure.

Each heating system has its own permissible strength limit. In other words, it can withstand different loads. To find out which working pressure in a closed heating system, it is necessary to add dynamic, pumped by pumps, to the static one created by the water column. For proper operation system, the pressure gauge readings must be stable. Pressure gauge – mechanical device, which measures the force with which water moves in a heating system. It consists of a spring, a pointer and a scale. Pressure gauges are installed in key locations. Thanks to them, you can find out what operating pressure is in the heating system, as well as identify faults in the pipeline during diagnostics.

Pressure drops

To compensate for differences, additional equipment is built into the circuit:

1. expansion tank;
2. emergency coolant release valve;
3. air vents.

Air testing - the heating system test pressure is raised to 1.5 bar, then lowered to 1 bar and left for five minutes. In this case, losses should not exceed 0.1 bar.

Water testing - increase the pressure to at least 2 bar. Perhaps more. Depends on operating pressure. The maximum operating pressure of the heating system must be multiplied by 1.5. In five minutes, losses should not exceed 0.2 bar.

Panel

Cold hydrostatic testing - 15 minutes with a pressure of 10 bar, loss no more than 0.1 bar. Hot testing - raising the temperature in the circuit to 60 degrees for seven hours.

Test with water, pumping 2.5 bar. Additionally, water heaters (3-4 bar) and pumping units are checked.

Heat networks

The permissible pressure in the heating system gradually increases to a level higher than the working pressure by 1.25, but not less than 16 bar.

Based on the test results, a report is drawn up, which is a document confirming the statements made in it. performance characteristics. These include, in particular, working pressure.

Working pressure in the heating system - the most important parameter, on which the functioning of the entire network depends. Deviations in one direction or another from the values ​​specified in the project not only reduce the efficiency of the heating circuit, but also significantly affect the operation of the equipment, and special cases may even disable it.

Of course, a certain pressure drop in the heating system is determined by the principle of its design, namely the difference in pressure in the supply and return pipelines. But if there are larger spikes, immediate action should be taken.

1. Static pressure. This component depends on the height of the column of water or other coolant in the pipe or container. Static pressure exists even if the working medium is at rest.
2. Dynamic pressure. Represents the force that acts on internal surfaces systems during the movement of water or other medium.

The concept of maximum operating pressure is distinguished. This is the maximum permissible value, exceeding which is fraught with destruction individual elements networks.

What pressure in the system should be considered optimal?

Table of maximum pressure in the heating system.

When designing heating, the coolant pressure in the system is calculated based on the number of floors of the building, total length pipelines and number of radiators. As a rule, for private houses and cottages, the optimal values ​​of medium pressure in the heating circuit are in the range from 1.5 to 2 atm.

For apartment buildings up to five floors high, connected to a central heating system, the network pressure is maintained at 2-4 atm. For nine- and ten-story buildings, a pressure of 5-7 atm is considered normal, and in higher buildings - 7-10 atm. The maximum pressure is recorded in the heating mains through which the coolant is transported from boiler houses to consumers. Here it reaches 12 atm.

For consumers located at different heights and at different distances from the boiler room, the pressure in the network has to be adjusted. To reduce it, pressure regulators are used, to increase it - pumping stations. However, it should be taken into account that a faulty regulator can cause an increase in pressure in certain areas of the system. In some cases, when the temperature drops, these devices can completely shut off the shut-off valves on the supply pipeline coming from the boiler plant.

To avoid such situations, the regulator settings are adjusted so that complete shutoff of the valves is impossible.

Autonomous heating systems

Expansion tank in an autonomous heating system.

In the absence district heating In houses, autonomous heating systems are installed, in which the coolant is heated by an individual low-power boiler. If the system communicates with the atmosphere through an expansion tank and the coolant circulates in it due to natural convection, it is called open. If there is no communication with the atmosphere, and the working medium circulates thanks to the pump, the system is called closed. As already mentioned, for normal functioning In such systems, the water pressure in them should be approximately 1.5-2 atm. This low figure is due to the relatively short length of pipelines, as well as the lack of a large number devices and fittings, resulting in relatively little hydraulic resistance. In addition, due to the low height of such houses, the static pressure in the lower sections of the circuit rarely exceeds 0.5 atm.

At the stage of starting the autonomous system, it is filled with cold coolant, maintaining a minimum pressure of closed systems heating 1.5 atm. There is no need to sound the alarm if, some time after filling, the pressure in the circuit drops. Pressure loss in in this case are caused by the release of air from the water, which dissolved in it when filling the pipelines. The circuit should be de-aired and completely filled with coolant, bringing its pressure to 1.5 atm.

After heating the coolant in the heating system, its pressure will increase slightly, reaching the calculated operating values.

Precautions

Device for measuring pressure.

Since when designing autonomous heating systems, in order to save money, a small safety margin is included, even a low pressure surge of up to 3 atm can cause depressurization of individual elements or their connections. In order to smooth out pressure drops due to unstable pump operation or changes in coolant temperature, an expansion tank is installed in a closed heating system. Unlike a similar device in the system open type, it has no communication with the atmosphere. One or more of its walls are made of elastic material, due to which the tank acts as a damper during pressure surges or water hammer.

The presence of an expansion tank does not always guarantee that pressure is maintained within optimal limits. In some cases it may exceed the maximum permissible values:

• if the expansion tank capacity is incorrectly selected;
• in case of malfunction of the circulation pump;
• when the coolant overheats, which is a consequence of malfunctions in the boiler automation;
• due to incomplete opening of shut-off valves after repairs or maintenance work;
• due to the appearance air lock(this phenomenon can provoke both an increase in pressure and a drop);
• when the throughput of the dirt filter decreases due to its excessive clogging.

Therefore, in order to avoid emergency situations when installing closed-type heating systems, it is mandatory to install safety valve, which will release excess coolant if the permissible pressure is exceeded.

What to do if the pressure in the heating system drops

Pressure in the expansion tank.

When operating autonomous heating systems, the most common emergency situations are those in which the pressure gradually or sharply decreases. They can be caused by two reasons:

• depressurization of system elements or their connections;
• problems with the boiler.

In the first case, the location of the leak should be located and its tightness restored. You can do this in two ways:

1. Visual inspection. This method is used in cases where the heating circuit is laid open method(not to be confused with an open type system), that is, all its pipelines, fittings and instruments are visible. First of all, carefully inspect the floor under the pipes and radiators, trying to detect puddles of water or traces of them. In addition, the location of the leak can be identified by traces of corrosion: characteristic rusty streaks form on radiators or at the joints of system elements when the seal is broken.
2. Using special equipment. If a visual inspection of the radiators does not yield anything, and the pipes are laid in a hidden way and cannot be inspected, you should seek the help of specialists. They have special equipment that will help detect leaks and fix them if the home owner is unable to do this themselves. Localizing the depressurization point is quite simple: water is drained from the heating circuit (for such cases, a drain valve is installed at the lowest point of the circuit during the installation stage), then air is pumped into it using a compressor. The location of the leak is determined by the characteristic sound that leaking air makes. Before starting the compressor, the boiler and radiators should be insulated using shut-off valves.

If problem area is one of the connections; it is additionally sealed with tow or FUM tape, and then tightened. The burst pipeline is cut out and a new one is welded in its place. Units that cannot be repaired are simply replaced.

If the tightness of pipelines and other elements is beyond doubt, and the pressure in a closed heating system still drops, you should look for the reasons for this phenomenon in the boiler. You should not carry out diagnostics yourself; this is a job for a specialist with the appropriate education. Most often the following defects are found in the boiler:

Installation of a heating system with a pressure gauge.

• the appearance of microcracks in the heat exchanger due to water hammer;
• factory defect;
• failure of the make-up valve.

A very common reason why the pressure in the system drops is the incorrect selection of the expansion tank capacity.

Although the previous section stated that this may cause increased pressure, there is no contradiction here. When the pressure in the heating system increases, the safety valve is activated. In this case, the coolant is discharged and its volume in the circuit decreases. As a result, the pressure will decrease over time.

Pressure control

For visual monitoring of pressure in the heating network, dial pressure gauges with a Bredan tube are most often used. Unlike digital instruments, such pressure gauges do not require connection electrical supply. IN automated systems use electrical contact sensors. At the outlet to the control and measuring device it is necessary to install three way valve. It allows you to isolate the pressure gauge from the network during maintenance or repair, and is also used to remove an air lock or reset the device to zero.

Instructions and rules governing the operation of heating systems, both autonomous and centralized, recommend installing pressure gauges at the following points:

1. Before the boiler installation (or boiler) and at the exit from it. At this point the pressure in the boiler is determined.
2. Before circulation pump and after it.
3. At the entrance of the heating main into a building or structure.
4. Before and after the pressure regulator.
5. At the filter inlet and outlet rough cleaning(mud collector) to control the level of its contamination.

Everything is under control measuring instruments must undergo regular verification to confirm the accuracy of the measurements they make.

In laminar flow, the sum of static and dynamic pressure remains constant. This amount corresponds to the static pressure in a fluid at rest.

The sum of static and dynamic pressure is called the total flow pressure. As the flow speed increases, the dynamic component total pressure increases, and the static decreases (see Fig. 4). In a flow at rest, the dynamic pressure is zero, and the total pressure is equal to the static pressure.

r

p o

static

pressure

dynamic

pressure

MEASUREMENT OF PRESSURE IN THE FLOW

• Static pressure is measured r st

pressure gauge installed

perpendicular to the direction

flow (in the simplest case -

open liquid pressure gauge

• Total pressure is measured with a pressure gauge, r full

Installed parallel to the direction

flow (Pitot tube)

difference between full and static

pressure and is measured by a combination r din

previous devices, which is called

Prandtl tube.

APPLICATION OF BERNOULLI'S LAW

In navigation.

When ships move on parallel courses when approaching in case of violation of the speed limit, there is a possibility of collision. Why? Let's turn to Fig. 4.9. It depicts two ships moving on parallel courses.

Fig.4.9

υ 1 υ 2 υ 1

р 1 р 2 р 1 υ 2>v 1

p 2<p 1

in one direction. Each of them cuts the water into two streams with its nose. The water that ends up between the ships, getting into the “narrowness”, is forced to pass through it at a speed υ 2, greater than the flow speed v 1 from the outside of the ships. Therefore, according to Bernoulli's law, the water pressure between ships p 1 will be less than water pressure p 2 from the outside. If there is a pressure difference, movement occurs from a zone of higher pressure to a zone of lower pressure - nature abhors a vacuum! – therefore, both ships will rush towards each other (the direction is indicated by the arrows). If in this situation the correspondence between the approach distance and the speed is violated, then there is a danger of collision - the so-called “suction” of ships. If ships move in parallel but oncoming courses, the “suction” effect also takes place. Therefore, when ships approach each other, navigation rules require reducing the speed to optimal value.

When the vessel moves in shallow water, the situation is similar (see Fig. 4.10). The water under the bottom of the ship finds itself in a “narrow place”, the flow speed

Fig.4.10

v 1,p 1 υ 1, p 1 υ 2 > υ 1

υ 2, р 2 р 2< p 1

increases, the pressure under the ship decreases - the ship seems to be attracted to the bottom. To avoid the possibility of running aground, it is necessary to reduce the speed to minimize this effect.

In aviation.

Knowledge and use of Bernoulli's law made it possible to create aircraft

heavier than air are airplanes, airplanes, helicopters, gyroplanes (small light helicopters). The fact is that the cross-section of the wing or blade of these machines has the so-called airfoil , causing lift force (see Fig. 4.11). This is achieved as follows. It's all about the “drop-shaped” shape of the airfoil. Experience shows that when the wing is placed in an air flow, vortices arise near the trailing edge of the wing, rotating counterclockwise in the case shown in Fig. 4.11. These vortices grow, break away from the wing and are carried away by the flow. The rest of the air mass near the wing receives the opposite rotation - clockwise - forming circulation around the wing (in Fig. 4.11 this circulation is depicted by a dotted closed line). Overlapping with the general flow, the circulation slightly slows down the air flow under the wing and slightly accelerates the air flow above the wing. Thus, a zone of lower pressure is formed above the wing than under the wing, which leads to the emergence of lift. F p, directed vertically upward. In addition to her, as a result of the movement of the aircraft on the wing

Fig.4.11

direction of movement of the aircraft

υ 2, р 2 υ 2 > υ 1

There are three more forces at work: 1). Gravity G, 2). Airplane engine thrust F t,

3). Air drag force F with. When all four forces are geometrically added, the resultant force is obtained F, which determines the direction of movement of the aircraft.

The greater the speed of the oncoming flow (and it depends on the thrust force of the engines), the greater the speed and lift force and drag force. These forces depend, in addition, on the shape of the wing profile, and on the angle at which the flow approaches the wing (the so-called angle of attack), as well as on the density of the oncoming flow: the higher the density, the greater these forces.

The wing profile is chosen so that it provides the greatest possible lift with the lowest possible drag. The theory of the emergence of the lifting force of a wing when air flows around it was given by the founder of the theory of aviation, the founder of the Russian school of aero- and hydrodynamics, Nikolai Egorovich Zhukovsky (1847-1921).

Airplanes designed to fly at different speeds have different wing sizes. Slow-flying transport aircraft must have large area wings, because at low speed the lift force per unit area of ​​the wing is small. High-speed aircraft also receive sufficient lift from small-area wings.

Because the lifting force of the wing decreases with decreasing air density, then for flight at high altitude the plane must move at a higher speed than near the ground.

Lift also occurs when the wing moves in water. This makes it possible to build hydrofoil ships. The hull of such vessels comes out of the water while moving - this reduces water resistance and allows you to achieve high speed progress. Because Since the density of water is many times greater than the density of air, it is possible to obtain sufficient lifting force of a hydrofoil with a relatively small area and moderate speed.

There is a type aircraft heavier than air, for which wings are not needed. These are helicopters. Helicopter blades also have an aerodynamic profile. The propeller creates vertical thrust regardless of whether the helicopter is moving or not - therefore, during operation propellers The helicopter can hang motionless in the air or rise vertically. To move the helicopter horizontally, it is necessary to create horizontal thrust. This is achieved by changing the angle of the blades, which is done using a special mechanism in the propeller hub. (The small propeller with a horizontal axis on the tail of the helicopter serves only to prevent the body of the helicopter from rotating in the direction opposite to the rotation of the large propeller.)

Kinetic energy of moving gas:

where m is the mass of moving gas, kg;

s - gas speed, m/s.

(2)

where V is the volume of moving gas, m 3;

- density, kg/m3.

Let's substitute (2) into (1), we get:

(3)

Let's find the energy of 1 m 3:

(4)

The total pressure is the sum of And
.

Total pressure in air flow equal to the sum of static and dynamic pressures and represents the energy saturation of 1 m 3 of gas.

Scheme of experiment for determining total pressure

Pitot-Prandtl tube

(1)

(2)

Equation (3) shows the operation of the tube.

- pressure in column I;

- pressure in column II.

Equivalent hole

If you make a hole with a cross-section F e through which the same amount of air will be supplied
, as through a pipeline at the same initial pressure h, then such a hole is called equivalent, i.e. passage through this equivalent hole replaces all resistance in the pipeline.

Let's find the size of the hole:

, (4)

where c is the gas flow rate.

Gas consumption:

(5)

From (2)
(6)

Approximately, because we do not take into account the jet narrowing coefficient.

- this is a conditional resistance, which is convenient to introduce into calculations when simplifying the actual complex systems. Pressure losses in pipelines are defined as the sum of losses in individual places of the pipeline and are calculated on the basis of experimental data given in reference books.

Losses in the pipeline occur at turns, bends, and during expansion and contraction of pipelines. Losses in an equal pipeline are also calculated using reference data:

Suction pipe

Fan housing

Discharge pipe

An equivalent hole that replaces the actual pipeline with its resistance.

- speed in the suction pipeline;

- outflow velocity through the equivalent opening;

- the pressure value under which gas moves in the suction pipe;

static and dynamic pressure in the outlet pipe;

- full pressure in the discharge pipe.

Through equivalent hole gas leaks under pressure , knowing , we find .

Example

What is the motor power to drive the fan if we know the previous data from 5.

Taking into account losses:

Where - monometric efficiency.

Where
- theoretical fan pressure.

Derivation of fan equations.

Asked by:

Find:

Solution:

Where
- air mass;

- initial radius of the blade;

- final radius of the blade;

- air speed;

- tangential speed;

- radial speed.

Divide by
:

;

Secondary mass:

,

;

Secondary operation - power supplied by the fan:

.

Lecture No. 31.

The characteristic shape of the blades.

- peripheral speed;

WITH– absolute particle velocity;

- relative speed.

,

.

Let's imagine our fan with inertia B.

Air enters the hole and is sprayed along the radius at a speed Cr. but we have:

,

Where IN– fan width;

r– radius.

.

Multiply by U:

.

Let's substitute
, we get:

.

Let's substitute the value
for radii
into the expression for our fan and we get:

Theoretically, the fan pressure depends on the angles (*).

We will replace through and substitute:

Divide the left and right sides into :

.

Where A And IN– replacement coefficients.

Let's build a dependency:

Depending on the angles
the fan will change its character.

In the figure, the rule of signs coincides with the first figure.

If an angle is drawn from the tangent to the radius in the direction of rotation, then this angle is considered positive.

1) In the first position: - positive, - negative.

2) Blades II: - negative, - positive – becomes close to zero and usually less. This is a high pressure fan.

3) Blades III:
are equal to zero. B=0. Medium pressure fan.

Basic relations for a fan.

,

where c is the air flow rate.

.

Let's write this equation in relation to our fan.

.

Divide the left and right sides by n:

.

Then we get:

.

Then
.

When solving for this case x=const, i.e. we'll get

Let's write down:
.

Then:
Then
- the first fan ratio (fan performances relate to each other as fan speeds).

Example:

- This is the second ratio of the fan (theoretical fan pressures are related as the squares of the rotation numbers).

If we take the same example, then
.

But we have
.

Then we get the third relation if instead
let's substitute
. We get the following:

- This is the third ratio (the power required to drive the fan is related to the cubes of the revolutions).

For the same example:

Fan calculation

Fan calculation data:

Asked:
- air flow (m 3 /sec).

The number of blades is also selected for design reasons - n,

- air density.

During the calculation process, we determine r 2 , d– diameter of the suction pipe,
.

The entire fan calculation is made based on the fan equation.

Scraper elevator

1) Resistance when loading the elevator:

G C- weight linear meter chains;

G G– weight of a linear meter of cargo;

L– length of the working branch;

f - friction coefficient.

3) Resistance in the idle branch:

Total effort:

.

Where - efficiency taking into account the number of sprockets m;

- efficiency taking into account the number of sprockets n;

- efficiency taking into account the rigidity of the chain.

Conveyor drive power:

,

Where - efficiency of the conveyor drive.

Bucket conveyors

It's bulky. Mainly used on stationary machines.

Thrower fan. It is used on silage combines and grain harvesters. Matter is subjected to specific action. High power consumption at higher productivity.

Belt conveyors.

Used on conventional headers

1)
(D'Alembert's principle).

Per particle mass m weight force acts mg, inertia force
, friction force.

,

.

Need to find X, which is equal to the length at which you need to gain speed from V 0 to V, equal to the conveyor speed.

,

Expression 4 is remarkable in the following case:

At
,
.

At angle
the particle can pick up the speed of the conveyor on the way L, equal to infinity.

Bunkers

There are several types of bunkers used:

with screw unloading

vibro-unloading

bunkers with free flow of granular medium are used on stationary machines

1. Bunkers with screw unloading

Screw unloader performance:

.

scraper elevator conveyor;

distribution auger hopper;

lower unloading auger;

inclined unloading auger;

- fill factor;

n– number of screw revolutions;

t– screw pitch;

- specific gravity of the material;

D– screw diameter.

2. Vibrating hopper

vibrator;

1. unloading tray;

   flat springs, elastic elements;

A– amplitude of hopper vibrations;

WITH– center of gravity.

Advantages: free formation is eliminated, design simplicity. The essence of the effect of vibration on a granular medium is pseudo-motion.

.

M– mass of the bunker;

X– its movement;

To 1 – coefficient taking into account speed resistance;

To 2 – spring stiffness;

- circular frequency or rotation speed of the vibrator shaft;

- phase of installation of weights in relation to the displacement of the hopper.

Let's find the amplitude of the bunker To 1 =0:

very few

,

- frequency of natural oscillations of the bunker.

,

At this frequency, the material begins to flow. There are flow rates at which the bunker is unloaded in 50 sec.

Hoarders. Collection of straw and chaff.

1. Stackers can be mounted or trailed, and they can be single-chamber or double-chamber;

2. Straw choppers with collection or spreading of chopped straw;

3. Spreaders;

4. Straw presses for collecting straw. There are mounted and trailed ones.

The operating pressure in the heating system is the most important parameter on which the functioning of the entire network depends. Deviations in one direction or another from the values ​​​​provided by the project not only reduce the efficiency of the heating circuit, but also significantly affect the operation of the equipment, and in special cases can even cause it to fail.

Of course, a certain pressure drop in the heating system is determined by the principle of its design, namely the difference in pressure in the supply and return pipelines. But if there are larger spikes, immediate action should be taken.

Terminology issues

Network pressure is divided into two components:

1. Static pressure. This component depends on the height of the column of water or other coolant in the pipe or container. Static pressure exists even if the working medium is at rest.
2. Dynamic pressure. It is a force that acts on the internal surfaces of the system when water or other medium moves.

The concept of maximum operating pressure is distinguished. This is the maximum permissible value, exceeding which can lead to the destruction of individual network elements.

What pressure in the system should be considered optimal?

When designing heating, the coolant pressure in the system is calculated based on the number of floors of the building, the total length of the pipelines and the number of radiators. As a rule, for private houses and cottages, the optimal values ​​of medium pressure in the heating circuit are in the range from 1.5 to 2 atm.

For apartment buildings up to five floors high, connected to a central heating system, the pressure in the network is maintained at 2-4 atm. For nine- and ten-story buildings, a pressure of 5-7 atm is considered normal, and in higher buildings - 7-10 atm. The maximum pressure is recorded in the heating mains through which the coolant is transported from boiler houses to consumers. Here it reaches 12 atm.

For consumers located at different heights and at different distances from the boiler room, the pressure in the network must be adjusted. To reduce it, pressure regulators are used, and to increase it, pumping stations are used. However, it should be taken into account that a faulty regulator can cause an increase in pressure in certain areas of the system. In some cases, when the temperature drops, these devices can completely shut off the shut-off valves on the supply pipeline coming from the boiler plant.

To avoid such situations, the regulator settings are adjusted so that complete shutoff of the valves is impossible.

Autonomous heating systems

In the absence of a centralized heating supply, autonomous heating systems are installed in houses, in which the coolant is heated by an individual low-power boiler. If the system communicates with the atmosphere through an expansion tank and the coolant circulates in it due to natural convection, it is called open. If there is no communication with the atmosphere, and the working medium circulates thanks to the pump, the system is called closed. As already mentioned, for the normal functioning of such systems, the water pressure in them should be approximately 1.5-2 atm. This low figure is due to the relatively short length of pipelines, as well as a small number of instruments and fittings, which results in relatively low hydraulic resistance. In addition, due to the low height of such houses, the static pressure in the lower sections of the circuit rarely exceeds 0.5 atm.

At the stage of launching the autonomous system, it is filled with cold coolant, maintaining a minimum pressure in closed heating systems of 1.5 atm. There is no need to sound the alarm if, some time after filling, the pressure in the circuit drops. Pressure losses in this case are caused by the release of air from the water, which dissolved in it when the pipelines were filled. The circuit should be de-aired and completely filled with coolant, bringing its pressure to 1.5 atm.

After heating the coolant in the heating system, its pressure will increase slightly, reaching the calculated operating values.

Precautions

Since when designing autonomous heating systems, in order to save money, a small safety margin is included, even a low pressure surge of up to 3 atm can cause depressurization of individual elements or their connections. In order to smooth out pressure drops due to unstable pump operation or changes in coolant temperature, an expansion tank is installed in a closed heating system. Unlike a similar device in an open type system, it does not communicate with the atmosphere. One or more of its walls are made of elastic material, due to which the tank acts as a damper during pressure surges or water hammer.

The presence of an expansion tank does not always guarantee that pressure is maintained within optimal limits. In some cases it may exceed the maximum permissible values:

• if the expansion tank capacity is incorrectly selected;
• in case of malfunction of the circulation pump;
• when the coolant overheats, which is a consequence of malfunctions in the boiler automation;
• due to incomplete opening of shut-off valves after repairs or maintenance work;
• due to the appearance of an air lock (this phenomenon can provoke both an increase in pressure and a drop);
• when the throughput of the dirt filter decreases due to its excessive clogging.

Therefore, in order to avoid emergency situations when installing closed-type heating systems, it is mandatory to install a safety valve that will release excess coolant if the permissible pressure is exceeded.

What to do if the pressure in the heating system drops

When operating autonomous heating systems, the most common emergency situations are those in which the pressure gradually or sharply decreases. They can be caused by two reasons:

• depressurization of system elements or their connections;
• problems with the boiler.

In the first case, the location of the leak should be located and its tightness restored. You can do this in two ways:

1. Visual inspection. This method is used in cases where the heating circuit is laid in an open manner (not to be confused with an open-type system), that is, all its pipelines, fittings and devices are visible. First of all, carefully inspect the floor under the pipes and radiators, trying to detect puddles of water or traces of them. In addition, the location of the leak can be identified by traces of corrosion: characteristic rusty streaks form on radiators or at the joints of system elements when the seal is broken.
2. Using special equipment. If a visual inspection of the radiators does not yield anything, and the pipes are laid in a hidden way and cannot be inspected, you should seek the help of specialists.
   and have special equipment that will help detect leaks and fix them if the home owner is not able to do this themselves. Localizing the depressurization point is quite simple: water is drained from the heating circuit (for such cases, a drain valve is installed at the lowest point of the circuit during the installation stage), then air is pumped into it using a compressor. The location of the leak is determined by the characteristic sound that leaking air makes. Before starting the compressor, the boiler and radiators should be insulated using shut-off valves.

If the problem area is one of the joints, it is additionally sealed with tow or FUM tape and then tightened. The burst pipeline is cut out and a new one is welded in its place. Units that cannot be repaired are simply replaced.

If the tightness of pipelines and other elements is beyond doubt, and the pressure in a closed heating system still drops, you should look for the reasons for this phenomenon in the boiler. You should not carry out diagnostics yourself; this is a job for a specialist with the appropriate education. Most often the following defects are found in the boiler:

• the appearance of microcracks in the heat exchanger due to water hammer;
• factory defect;
• failure of the make-up valve.

A very common reason why the pressure in the system drops is the incorrect selection of the expansion tank capacity.

Although the previous section stated that this may cause increased pressure, there is no contradiction here. When the pressure in the heating system increases, the safety valve is activated. In this case, the coolant is discharged and its volume in the circuit decreases. As a result, the pressure will decrease over time.

Pressure control

For visual monitoring of pressure in the heating network, dial pressure gauges with a Bredan tube are most often used. Unlike digital instruments, such pressure gauges do not require an electrical power connection. Automated systems use electrical contact sensors. A three-way valve must be installed at the outlet to the control and measuring device. It allows you to isolate the pressure gauge from the network during maintenance or repair, and is also used to remove an air lock or reset the device to zero.

Instructions and rules governing the operation of heating systems, both autonomous and centralized, recommend installing pressure gauges at the following points:

1. Before the boiler installation (or boiler) and at the exit from it. At this point the pressure in the boiler is determined.
2. Before and after the circulation pump.
3. At the entrance of the heating main into a building or structure.
4. Before and after the pressure regulator.
5. At the inlet and outlet of the coarse filter (mud filter) to control its level of contamination.

All control and measuring instruments must undergo regular verification to confirm the accuracy of the measurements they perform.

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What pressure value is considered normal?

The pressure in an autonomously operating heating system of a private house should be 1.5-2 atmospheres. In houses connected to a centralized heating network, this value depends on the number of floors of the building. In low-rise buildings, the pressure in the heating system is in the range of 2-4 atmospheres. In nine-story buildings this indicator equal to 5-7 atmospheres. For heating systems of high-rise buildings, the optimal pressure value is considered to be 7-10 atmospheres. In the heating main running underground from the thermal power plant to the heat consumption points, the coolant is supplied under a pressure of 12 atm.

To reduce the pressure of hot water on the lower floors of apartment buildings, pressure regulators are used. Pumping equipment allows you to increase the coolant pressure on the upper floors.

Influence of coolant temperature

After completing the installation of heating equipment in a private house, they begin pumping coolant into the system. At the same time, the minimum possible pressure is created in the network, equal to 1.5 atm. This value will increase as the coolant heats up, since it expands in accordance with the laws of physics. By changing the temperature of the coolant, you can adjust the pressure in the heating network.

You can automate the control of operating pressure in the heating system by installing expansion tanks that prevent an excessive increase in pressure. These devices come into operation when a pressure level of 2 atm is reached. Excess heated coolant is removed by expansion tanks, thereby maintaining the pressure at the required level. It may happen that the containers expansion tank not enough to take away excess water. At the same time, the pressure in the system approaches the critical level, which is at the level of 3 atm. The situation is saved by a safety valve, which allows you to keep the heating system intact by freeing it from excess coolant volume.

At natural circulation The coolant creates static pressure in the heating system, which is measured at 1 atmosphere for every 10 meters of water column height. When installing circulation pumps, the dynamic pressure value is added to the static indicator, indicating the force with which the forcedly moving coolant presses on the walls of the pipeline. The maximum pressure in the autonomous heating system is set taking into account the characteristics of the heating equipment used during installation. For example, when choosing cast iron batteries It must be taken into account that they are designed for operation at a pressure not exceeding 0.6 MPa.

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Types of pressure

To understand why there is pressure in the heating system, let’s remember the physics course and determine what pressure in the heating system is. Essentially, this is the effect of liquid on the internal walls of the system elements.

In this case, the working pressure in the heating system is the pressure that allows the system to operate when the heating device and pump are turned on. It should be noted that this value is the sum of: the static pressure in the heating system exerted by the coolant column, and the dynamic pressure that occurs during operation of the circulation pump.

In this case, the working pressure is the value that provides normal work all system components (pump, heating device, expansion tank), that is, the optimal pressure in the heating system. It should be noted that not all types of radiators are able to withstand the maximum pressure in the heating system. The most “resistant” are bimetallic radiators(that is, consisting of two components - for example, copper and steel).

But monometallic radiators work fully only when optimal indicator pressure, exceeding which can have an extremely negative effect and the maximum operating pressure of the heating system will cause difficulties. In addition, this type of radiator is extremely poorly resistant to hydraulic shocks that sometimes occur in the system (sharp abrupt increase in pressure). Such impacts can significantly damage not only radiators, but also other elements of the heating system. In most cases, the cause of water hammer is simple negligence and inattention of operating personnel. Even if you installed the system yourself, this does not exclude the occurrence of such defects.

At trial run The heating system should be tested in such a way as the water pressure in the heating system. That is, the system starts up with a pressure that exceeds normal operating pressure by approximately 1.5 times.

This allows you not only to check the quality of radiators, but also to detect minor leaks and system defects (if any). This simple method allows you to fix some problems before you start heating season, determining the minimum pressure in the heating system.

In most multi-story buildings, the pressure level is quite high. And carrying out such checks - important need, which allows you to monitor the functionality of the system. It is noteworthy that reducing the pressure in it to a level that is quite a bit below the working level can lead to serious damage. Few people know, but in multi-storey buildings, the coolant pressure in the heating system can reach 16 atmospheres and higher.

Impact on the system by pressure

There are two possible options checking the functionality of the heating system using pressure. In the first case, the check takes place in separate sections. Of course, this is a more painstaking and lengthy process, but at the same time, it allows you to more thoroughly examine the integrity of the system section and the pressure in the heating pipes. In addition, if a breakdown is detected, it is much easier to fix it - after all, the area is already blocked. Accordingly, there is no need to waste time determining the location of a fault throughout the entire system, which the pressure sensor in the heating system will not show you.

The second method consists precisely in checking the entire system at the same time. Perhaps the only advantage of this method is that it is more short terms carrying out the test.

Regardless of which test principle is chosen, it follows a single scheme.

• Air is removed from the system (or a separate segment of it).
• the permissible pressure in the heating system is supplied, which is 1.5 times higher than the working one.

After the pressure test is completed, the system undergoes another leak test. It is performed in two stages. First of all, the system is filled with cold coolant. Next connects heating element, and the system is filled with hot coolant. Of course, the test is considered successful if no leakage occurs. If there is a breakdown, repairs are made. Only after this can we say with confidence that the system is completely ready for the heating season and that the required pressure in the heating pipes has been met.

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Introductory information on the topic

First of all, we propose to consider why excess pressure (above atmospheric pressure) is created in pipelines and how it is measured. Let's start from the end: the amount of water pressure in a closed heating system is usually displayed in the following units:

• 1 Bar = 10 m water column;
• 1 MPa equals 10 Bar or 100 m of water. Art.;
• 1 kgf/cm² – the same as 1 technical atmosphere (Atm.) = 0.98 Bar.

For reference. Kilogram-force per cm² is a measurement often used during Soviet times. On at the moment pressure is usually measured in more convenient metric units - MPa or Bar.

Simplified heating scheme for a 3-story mansion

Next, imagine a three-story cottage with a ceiling height of 3 m, which needs to be heated in winter period. To do this, batteries are installed on both floors, connected to a common riser coming from the boiler, as shown in the diagram. The actual pressure in the resulting closed heating system will consist of three components:

1. A column of water in a pipeline presses with a force equal to its height. In our example it is 6 m or 0.6 Bar (0.06 MPa).
2. The pressure created by the circulation pump. It forces the coolant to move at the required speed and overcome the resistance of three forces: gravity, friction of the liquid against the walls of the pipes and obstacles in the form of reinforcement and fittings (restrictions, tees, turns, etc.).
3. Additional pressure arising from thermal expansion of the liquid. Practice shows that cold water with a temperature of 10 °C after heating to 100 °C adds about 5% of its original volume.

Note. The static pressure of the liquid column varies depending on the measurement location. When the pump is turned off, the pressure gauge at the bottom point of the system will show the maximum value - 0.6 Bar, and at the top - zero.

Thermal expansion liquids

A very important point. In order to supply the required amount of heat to the premises, it is necessary to ensure the required water temperature and its flow rate - two main parameters for the operation of water heating. The resulting pressure is only a consequence of the system’s operation, and not the cause. Theoretically, it can be anything as long as the radiators and boiler installation can withstand it.

This gives rise to the concept of what operating pressure is in a heating system: this is the maximum valid value, registered in technical documentation equipment - boiler or batteries. Regulatory documents they require that in private homes it should not exceed 0.3 MPa, although some cheap units are not able to withstand even 0.2 MPa.

Why raise the pressure?

The pressure in the supply line is higher than in return line. This difference characterizes the heating efficiency as follows:

1. A small difference between the supply and return makes it clear that the coolant successfully overcomes all resistance and transfers the calculated amount of energy to the premises.
2. An increased pressure drop indicates increased section resistance, decreased flow velocity and excessive cooling. That is, there is insufficient water flow and heat transfer to the rooms.

For reference. According to the standards, the optimal pressure difference in the supply and return pipelines should be in the range of 0.05-0.1 Bar, maximum 0.2 Bar. If the readings of 2 pressure gauges installed on the line differ more, then the system is not designed correctly or needs repair (flushing).

To avoid high drops on long heat supply branches with a large number of batteries equipped with thermostatic valves, a automatic regulator flow rate as shown in the diagram.

So, excess pressure in a closed heating network created for the following reasons:

• to ensure forced movement of the coolant at the required speed and flow rate;
• to monitor the condition of the system using a pressure gauge and recharge or repair it in time;
• Coolant under pressure heats up faster, and in the event of emergency overheating, it boils at a higher temperature.

We are interested in the second item on the list - the pressure gauge readings as a characteristic of the serviceability and performance of the heating system. They are of interest to homeowners and apartment owners who independently maintain home communications and equipment.

Pressure in pipes of apartment buildings

From the contents of the previous sections, it becomes clear that the amount of heating in the central heating pipelines of high-rise buildings depends on the floor on which the apartment is located. The situation is as follows: if residents of the first two floors can roughly navigate using a pressure gauge installed in the basement heating unit, then the real pressure in the remaining dwellings remains unknown, since it drops with every meter of water rise.

Note. In new buildings with apartment-by-apartment heating distribution from a common riser, where floor-to-floor heating points, you can control the coolant pressure at the entrance to each apartment.

Moreover, knowing the amount of pressure in a centralized network is of no practical use, since the owner cannot influence it. Although some people argue this way: if the pressure in the line has dropped, it means that less heat is supplied, which is a mistake. A simple example: turn off the return tap in the basement and you will see a jump in the pressure gauge needle, but the movement of water will stop and the supply of thermal energy will stop.

This is what the heating point looks like at the entrance

Now specifically about the numbers. The diameters of the heat supply networks and the power of the pumps supplied from the boiler room are calculated so as to ensure the rise required quantity coolant up to last floor. This means that at the entrance to a multi-storey building the working pressure in the heating system will be:

• in old five-story buildings, where they still meet today cast iron radiators, - no more than 7 Bar;
• in nine-story Soviet-built buildings, the minimum value is 5 Bar, and the maximum depends on the proximity of the boiler room to the pumps, but not higher than 10 Bar;
• in high-rise buildings - no more than 15 bar.

For reference. At least once a year pipelines and heating devices must be tested under a pressure 25% greater than the working pressure. But in real life Utilities do not risk checking house systems and limit themselves to testing external heating networks.

The information presented is only useful in terms of choosing new radiators and polymer pipes. It is clear that in buildings high number of storeys Cast iron and steel panel batteries rated for a maximum of 1 MPa should not be installed, as described in detail in our selection guide and video from an expert:

Pressure indicators in a private home and the reasons for its drop

In closed heating systems of country houses and cottages, it is customary to withstand the following pressure values:

Important point. It is not for nothing that we indicated what pressure should be provided when cold system heating. The fact is that the vast majority of imported gas boilers equipped modern automation, is designed to start with a minimum pressure of 0.8-1 Bar and in its absence it simply will not turn on.

How to properly remove air from heating lines and create the required pressure is described in a separate instruction. Here we will list the reasons why, after successful commissioning, pressure indicators may decrease, up to automatic shutdown wall-mounted boiler:

1. Residual air escapes from the pipeline network, heated floors and heating equipment ducts. Its place is taken by water, which is recorded by the pressure gauge falling to 1-1.3 Bar.
2. Due to a leak in the spool, the air chamber of the expansion tank was emptied. The membrane is pulled into reverse side and the container is filled with water. After heating, the pressure in the system rises to a critical level, causing the coolant to be discharged through the safety valve and the pressure again drops to a minimum.
3. The same thing, only after the expansion tank membrane breaks.
4. Minor leaks at joints pipeline fittings, fittings or pipes themselves as a result of damage. Example - heating circuits heated floors where the leak may remain unnoticed for a long time.
5. Boiler coil leaking indirect heating or buffer tank. Then pressure surges are observed depending on the operation of the water supply: the taps are open - the pressure gauge readings fall, closed - they rise (the water supply is pressed through a crack in the heat exchanger).

The master will tell you more about the causes of pressure drops and how to eliminate them in his video:

Conclusion

As you can see, the importance of pressure in centralized heating networks is somewhat exaggerated. Even if the owner of the apartment is aware that he should have 0.7 MPa in his pipes, this gives him little. Except correct selection radiators and pipes for replacing lines.

Hand pump refill

In a private house, the picture is different: the pressure gauge readings, and even a puddle near the safety valve, serve as an indicator of minor or significant malfunctions. These things need to be monitored and reacted in time by replenishing the system in order to raise the pressure to normal. Don't forget about expansion tank- pump up on time air chamber and monitor the integrity of the membrane.

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Why is there pressure in the system?

Many consumers are interested in why there is pressure in the heating system and what depends on it. The fact is that it has a direct impact on the efficiency and quality of heating the premises of the house. Thanks to the working pressure it is possible to achieve best performance heat supply system due to the guaranteed flow of coolant into pipelines and radiators in each apartment multi-storey building.

Constant and stable pressure in the city heating system allows you to reduce heat loss and deliver coolant to consumers at almost the same temperature as when heating water in a boiler room heating unit (read also: “Coolant temperature in the heating system: norms”).

Types of working pressure in heating structures

The pressure in the heating design of a multi-story building is of several types:

1. The static pressure of a heating system is an indicator of the force with which the volume of liquid, depending on the height, acts on pipelines and radiators. In this case, when carrying out calculations, the pressure level on the surface of the liquid is zero.
2. Dynamic pressure occurs during movement coolant liquid through pipes. It affects the pipeline and radiators from the inside.
3. The permissible (maximum) operating pressure in the heating system is a parameter for the normal and trouble-free functioning of the heat supply structure.

Normal pressure indicators

In all domestic multi-storey buildings, built both several decades ago and in new buildings, the heating system operates according to closed schemes using forced movement of the coolant. Operating conditions are considered ideal when the heating system operates under a pressure of 8-9.5 atmospheres. But in old houses, a loss of pressure may be observed in the heat supply structure, and accordingly the pressure indicators may drop to 5 -5.5 atmospheres. Read also: “What is pressure drop in a heating system.”

When choosing pipes and radiators to replace them in an apartment located in multi-storey building, initial indicators should be taken into account. Otherwise, the heating equipment will work unstably and even complete destruction of the heating supply circuit, which costs a lot of money, is possible.

What pressure should be in the heating system of a multi-storey building is dictated by standards and other regulatory documents.

As a rule, it is impossible to achieve the required parameters according to GOST, since performance indicators are influenced by various factors:

1. Equipment power required for supplying coolant. The pressure parameters in the heating system of a high-rise building are determined at heating stations, where the coolant is heated for supply through pipes to the radiators.
2. Equipment condition. Both dynamic and static pressure in the heat supply structure are directly affected by the level of wear of boiler room elements such as heat generators and pumps. The distance from the house to the heating station is of no small importance.
3. Diameter of pipelines in the apartment. If, when carrying out repairs with their own hands, the apartment owners installed pipes larger diameter than in the inlet pipeline, a decrease in pressure parameters will occur.
4. Location separate apartment in a high-rise building. Of course, the required pressure value is determined in accordance with the norms and requirements, but in practice a lot depends on what floor the apartment is on and its distance from the common riser. Even when living rooms are located close to the riser, the pressure of the coolant in corner rooms is always lower, since there is often an extreme point of the pipelines.
5. Degree of wear of pipes and batteries. When the elements of the heating system located in the apartment have served for decades, some reduction in equipment parameters and performance cannot be avoided. When such problems occur, it is advisable to initially replace worn pipes and radiators and then emergency situations will be avoided.

Test pressure

Residents of apartment buildings know how utility services, together with specialists from energy companies, check the coolant pressure in the heating system. Usually, before the start of the heating season, they supply coolant into the pipes and radiators under pressure, the value of which approaches critical levels.

Pressure is used when testing the heating system in order to test the performance of all elements of the heat supply structure in extreme conditions and find out how efficiently heat will be transferred from the boiler room to a multi-story building.

When test pressure is applied to the heating system, its elements often come into emergency condition and require repairs, as worn-out pipes begin to leak and holes form in the radiators. Timely replacement of outdated heating equipment in the apartment will help to avoid such troubles.

During testing, parameters are monitored using special devices installed in the lowest (usually a basement) and highest ( attic space) points of the high-rise building. All measurements taken are subsequently analyzed by specialists. If there are deviations, it is necessary to detect problems and correct them immediately.

Checking the tightness of the heating system

To ensure effective and reliable operation heating systems, not only check the coolant pressure, but also test the equipment for leaks. How this happens can be seen in the photo. As a result, you can monitor the presence of leaks and prevent equipment breakdown at the most crucial moment.

The tightness test is carried out in two stages:

• cold water test. Pipelines and batteries in a multi-story building are filled with coolant without heating it, and pressure readings are measured. Moreover, its value during the first 30 minutes cannot be less than the standard 0.06 MPa. After 2 hours, losses cannot be more than 0.02 MPa. In the absence of gusts, the heating system of the high-rise building will continue to function without problems;
• test using hot coolant. Heating system tested before starting heating season. Water is supplied under a certain compression, its value should be the highest for the equipment.

To achieve the optimal pressure value in the heating system, it is best to entrust the calculation of its arrangement to specialist heating engineers. Employees of such companies can not only carry out the appropriate tests, but also wash all its elements.

Testing is carried out before starting up the heating equipment, otherwise the cost of an error can be too expensive, and, as is known, it is quite difficult to eliminate an accident at sub-zero temperatures.

The pressure parameters in the heat supply scheme of a multi-storey building determine how comfortable you can live in each room. Unlike their own home ownership with an autonomous heating system in a high-rise building, apartment owners do not have the opportunity to independently adjust the parameters heating structure, including temperature and coolant supply.

But residents of multi-storey buildings, if desired, can install such measuring instruments as pressure gauges in the basement and, in case of the slightest deviations in pressure from the norm, report this to the relevant utility services. If, after all the steps taken, consumers are still unhappy with the temperature in the apartment, perhaps they should consider organizing alternative heating.

As a rule, the pressure in domestic pipelines multi-storey buildings does not exceed the maximum standards, but still installing an individual pressure gauge will not be superfluous.