Pressure regulating valve. Calculation and Selection of the Pressure Regulator "After You"

In pipeline systems, when transporting various substances, the pressure must be maintained at a set level.

This is very important for heat supply systems, ventilation, fuel supply, for the operation of pumping station equipment, heating points, etc.

To maintain pressure in automatic mode, direct-acting regulators are installed, which operate at the expense of the energy of a moving stream, and indirect-acting, requiring external energy sources.

Such devices maintain flow pressure in the direction of travel until it is installed. The water pressure is maintained at the required level by changing the size of the flow area.

Device, principle of operation and classification

Manufacturers produce a wide range of products that differ in design, materials from which they are made, manufacturing technology, dimensions and weight, principle of operation, but any of them must contain the following elements:

case (cast iron, steel, brass, copper);

• control part (piston, bellows, diaphragm);

  setter (spring, lever-load, pneumatic);

  impulse line.

The principle of operation is based on the use of water pressure to move the valve plug, while the degree of opening of the passage section is proportional to the deviation of the controlled pressure from the required value.

The second name of this type of control valves: proportional regulators. The pressure regulator to itself automatically maintains the working pressure of the transported medium and, if it exceeds the required value, it opens the section until it equals the set value.

The most commonly used spring and diaphragm pressure regulators. For spring pressure regulators, the measuring element is the valve plug, and for membrane pressure regulators, the membrane.

Both types have a spring adjuster. Such equipment is characterized by high accuracy of maintaining the pressure value, simplicity of design and maintainability.

The classification is based on constructive differences:

principle of action (direct and indirect);

loading method (spring, lever-load or pneumatic);

design of the working body (single and double seats);

type of sensitive element (piston, bellows, membrane);

plunger type (piston, poppet, hollow, rod, multistage);

method of connection to the pipeline (flanged, coupling, by welding);

conditional pass in mm;

throughput in m 3 / hour.

The pressure regulator with indirect action has in its design a pressure sensor that performs the functions of a measuring element, a programmable controller and a control valve with an electric drive. The latter performs the function of the actuator.

Key benefits of pressure regulators

Product benefits include:

a wide range of manufactured devices, which allows you to choose it for any need;

the ability to stabilize the pressure of the transported medium;

the ability to maintain pressure in various ranges;

adjustment accuracy;

easy assembly and dismantling;

the ability to significantly reduce the noise level in pipelines;

maintainability;

high degree of reliability;

long service life.

For products of indirect action, this also includes the fact that the work can be controlled remotely.

Dependence on the need to have an external control source for this type of valve does not always make it possible to use this equipment.

Specifications

When choosing a pressure regulator to yourself, special attention is paid to such factors:

conditional passage, indicated in mm;

nominal working pressure in bar, MPa or kgf / cm 2;

throughput in m 3 / hour;

setting range;

operating temperature range in which it can operate;

method of connection to the pipeline.

If you need a pressure regulator to yourself and control valves for heating and heat supply, contact the professionals

by free phone: 8-800-77-55-449

or by email on the site

www.gardarikamarket.ru

The principle of operation of the pressure regulator water is based on the operation of the membrane box due to the energy of the working medium in the pipeline. Direct acting pressure regulators consist of three main elements: a valve body, a membrane block and a spring setter. A sensitive membrane is rigidly fixed inside the membrane block, which divides the membrane space into two parts. The membrane is rigidly fixed to the regulator cone, thus, acting on the membrane, the valve cone closes or opens the flow area of ​​the regulator and regulates the pressure. The membrane (through the impulse tube (for RD122 differential pressure regulators), or directly through the valve body (as in RD102V and RD103V)) is acted upon by the working medium (water, steam, etc.), on the opposite side the membrane experiences a spring force. The direction of the pressure of the spring and the working medium is determined by the type of pressure regulator: "differential pressure", "pressure regulator upstream" or "regulator downstream".

When the set pressure in the regulator is equal to the actual pressure in the system (that is, the system is in equilibrium), the force of the adjusted spring is equal to the pressure of the working medium. The higher the pressure in the system must be maintained, the greater the compression ratio of the spring. When the pressure in the system changes, the impulse through the impulse pipeline directly affects the diaphragm, which in turn affects the regulator cone. Depending on the type (upstream or downstream pressure regulator), the regulator opens or closes as the pressure rises.

For example, the downstream pressure regulator, in the absence of pressure in the system (Fig. 1.1), is normally open. When the pressure rises and exceeds the value set with the setting spring according to the pressure gauge downstream of the regulator, the valve cone begins to close until the pressure previously set using the spring block equals the actual pressure downstream of the regulator.

The downstream pressure regulator valve (Fig. 1.2.) is normally open when there is no pressure. (The figure shows the installation diagram of the regulator on the input branch). Pressure impulses are supplied through the impulse tubes from the direct (+) and return (-) pipelines. These pulses act on the diaphragm and (depending on the differential pressure set in advance using the adjusting screw) the change in differential pressure causes the regulator cone (3) to shift and close or open it until the pressure differential reaches the value set on the spring block .

Pumping liquids is a rather complex, dynamic process. Over time, due to the influence of external factors, the direction of movement, flow rate, and pressure in the pipeline may change. Also, the influence of local resistances arising at the installation sites of valves, pipeline rotation and when changing the flow area is very strong.

For stable and safe operation of the connected equipment, stabilization of the internal network pressure is necessary. This requires the installation of additional equipment regulating the water pressure in the network.

Model range of control valves

Dorot manufactures a range of valves to control the flow of water in a wide range of applications. The principle of operation of the water pressure regulator served as the basis for the classification of the model range:

• pressure reduction valve PS - regulates the inlet section of the pipeline (to itself);

• pressure maintaining valve PR - outlet pressure regulation (after itself);

• differential valve DI - maintains a constant pressure difference between the inlet and outlet.

• the QR control valve, designed to relieve emergency overpressure, stands apart. This model performs the function of a fuse and is mounted not in the main pipeline itself, but on a separate outlet.

How pressure is regulated

The principle of operation of the water pressure regulator is based on the transfer of pressure from the pipeline to the control chamber of the valve. Depending on whether this pressure exceeds or falls below the set threshold value, the shut-off membrane reduces or increases the flow area. The required pressure value, which will determine the operation of the valve, is set on the pilot regulator.

There are several modes of operation of the valve

Maintaining a constant pressure to itself - the valve closes completely when the inlet pressure drops below the threshold value. With increasing pressure, the valve will open, increasing the flow area, thereby reducing the pressure in the system;

The principle of operation of the water pressure regulator after itself is the opposite. When the pressure drops below the set value, the valve will be in the fully open position. With an increase in inlet pressure, the valve will automatically close, keeping the pressure at the outlet section of the network constant;

Maintaining a constant pressure difference at the inlet and outlet is realized by changing the flow area. With an increase in inlet pressure, the valve closes, with a decrease, on the contrary, it begins to open.

Design

In general, the approximate design of the valve consists of the following elements:

• frame;

• control chamber;

• locking element;

• control pilot.

By design, Dorot control valves are available in the 100, 300, 500 series. The main difference is how the water pressure regulator works. Those. depending on the type of series, the design and orientation of the working locking element vary:

• series 100 - spring-loaded diaphragm moving in a vertical plane;

• series 300 - spring-loaded stem with vertical movement;

• series 500 - obliquely moving stem.

Pressure regulator bodies can be made of cast iron or bronze. According to the type of connection to the pipeline, a flanged, threaded or quick-connect connection on clamps (Viktaulik) can be implemented.

Advantages of fittings

Dorot pressure control valves are different

• simplicity and reliability of the design;

• use of high-strength corrosion-resistant materials;

• ease and simplicity of installation and maintenance;

• long period of operation.

The company "NEMEN" offers to purchase pressure regulators "to yourself" of various sizes. You can buy equipment with a capacity (Kvs) from 3.2 to 400 m³/h from us.

Purpose

The regulator "to itself" is a type designed to change the parameters of the working medium in the system circuit or a given range in a certain section of it, located before the valve, by increasing or decreasing the flow area. The regulator is controlled directly from the working medium.

Regulator design

Valve. Consists of:

- housing made of:

• steel grade GP240GH,
• gray cast iron EN-GJL-250 ,
• spheroidal cast iron EN-GJS-400-18LT;

- plates and seats made of stainless steel X17CrNi6-2, X6CrNiMoTi 17-12-2 and seals made of metal or polymers (PTFE, EPDM, NBR).

Servo. It consists of a body made of acid-resistant stainless steel X6CrNiTi18-10 and a membrane. The diaphragm body is made of C22 steel, the seal is made of reinforced EPDM polymer or other materials depending on the working environment.

The set of controllers. It consists of steel springs and setting elements made of carbon steel.

Types of regulators

Direct action. The regulating body moves when using the energy that the regulated flow of the working medium has. Direct acting pressure regulators are throttling devices actuated by a diaphragm under regulated pressure. Any changes in the pressure of the medium cause a displacement of the membrane, due to which the flow area of ​​the throttle device changes. In view of this, the amount of medium passed by the regulator decreases or increases.

Indirect action. The regulating body moves under the influence of energy from a third-party source. Regulators of this type are equipped with an auxiliary device - a command device. Balancing the forces from the pressure of the medium on the membrane is carried out using the pressure set by the command device. Such devices have an amplifier that receives and amplifies the measuring pulse.

Wiring diagram

Mounted on horizontal sections of the system. The direction of the flow of the working medium must correspond to the indication of the arrow on the body of the device. If the temperature of the medium in the pipeline does not exceed 100 °C, then the position of the regulator is chosen arbitrarily. At medium temperatures above 100 °C, the device is mounted with the drive downwards. To ensure stable operation of the shut-off valves, a strainer is installed in front of the regulator, and a stuffing box valve ZWD is mounted at the point of impulse selection.

Calculation of the pressure regulator "after itself" consists in determining the throughput of the regulator, the required setting range, checking for noise and cavitation.

Bandwidth calculation

The dependence of head loss on flow through the pressure regulator is called capacity - Kvs.

Kvs - capacity, numerically equal to the flow rate in m³ / h, through a fully open valve of the pressure regulator, at which the pressure loss on it is 1 bar.

Kv - the same, with a partial opening of the regulator shutter.

Knowing that when the flow rate changes by “n” times, the pressure loss on the regulator changes by “n” squared times, it is not difficult to determine the required Kv of the pressure regulator by substituting the calculated flow rate and excess pressure into the equation.

Some manufacturers recommend choosing a pressure regulator with the nearest higher Kvs value to the Kv value obtained. This selection approach allows more accurate regulation of flow rates below the specified value in the calculation, but does not make it possible to increase the flow rate above the specified value, which quite often has to be exceeded. We do not criticize the above method, but we recommend selecting pressure regulators "downstream" in such a way that the required flow rate is in the range from 50 to 70% of the stroke. The pressure regulator, calculated in this way, will be able with sufficient accuracy both to reduce the flow rate relative to the specified one, and to slightly increase it.

The above calculation algorithm lists downstream pressure regulators for which the required Kv value falls within the stroke range of 40 to 70%.

The results of the selection show the percentage of opening of the pressure regulator gate, at which a given excess pressure is throttled at a given flow rate.

Setting range selection

The setting range of the pressure regulator depends on the compression force of the spring. Some pressure regulators are equipped as standard with one spring and have only one pressure setting range, and some can be equipped with springs of different stiffness and have several setting ranges. The pressure that the pressure regulator will maintain "after itself" should be approximately in the middle third of the control range.

The above algorithm for selecting a pressure regulator displays a list of regulators for which the specified pressure falls within the range from 20 to 80% of the range of supported pressures.

When choosing the setting range, it must be taken into account that the permissible error in the spring calibration at the limit values ​​of the setting range is 10%.

Calculation of the regulator for the occurrence of cavitation

Cavitation is the formation of steam bubbles in a water stream, which manifests itself when the pressure in it decreases below the saturation pressure of water vapor. The Bernoulli equation describes the effect of increasing the flow velocity and reducing the pressure in it, which occurs when the flow section narrows. The flow area between the valve and the seat of the pressure regulator is the very narrowing, the pressure in which can drop to saturation pressure, and the place where cavitation is most likely to form. Vapor bubbles are unstable, they appear sharply and also collapse sharply, this leads to metal particles being eaten out of the regulator shutter, which will inevitably cause premature wear. In addition to wear, cavitation leads to increased noise during operation of the regulator.

The main factors affecting the occurrence of cavitation:

• Water temperature - the higher it is, the greater the likelihood of cavitation.


• Water pressure - in front of the pressure regulator, the higher it is, the less likely it is to cause cavitation.


• Throttled pressure - the higher it is, the higher the likelihood of cavitation.


• The cavitation characteristic of the regulator is determined by the characteristics of the throttling element of the regulator. The cavitation coefficient is different for different types of pressure regulators and should be indicated in their technical characteristics, but since most manufacturers do not indicate this value, the calculation algorithm includes a range of the most probable cavitation coefficients.

As a result of the cavitation test, the following result can be produced:

• "No" - there will definitely be no cavitation.
• "Possible" - cavitation may occur on valves of some designs, it is recommended to change one of the above-described influence factors.
• "Yes" - cavitation will definitely be, change one of the factors influencing the occurrence of cavitation.

Calculation of the regulator for the occurrence of noise

High flow rates at the pressure regulator inlet can cause high noise levels. For most rooms where pressure regulators are installed, the permissible noise level is 35-40 dB(A) which corresponds to a velocity in the valve inlet of approximately 3m/s. Therefore, when selecting a pressure regulator, it is recommended not to exceed the indicated speed.