Shut-off valve regulating the angular direction of flow. Control valves
Control valves are a type of shut-off valve. It is designed to control the flow of a gaseous or liquid medium that is transported through a pipeline in various technological systems.
- Control and shut-off valves - main parameters
Control valves. Main varieties
In Russia they are traditionally divided into the following types:
Regulatory
Control valves are wide and actively used to constantly adjust the flow of the working medium from the minimum to the maximum level (the adjustment is carried out by blocking the nominal orifice). In the first case, the valve is completely closed, and in the second, it is completely open, ensuring the unhindered flow of a liquid or gaseous medium and, accordingly, the highest flow.
Shut-off
Shut-off valves (sometimes also called shut-off valves) regulate the flow discretely, providing free passage for liquid (gas) or its shutoff, having actually two positions. At the same time, in the closed position, shut-off valves allow small leaks, so it is impossible to talk about the complete tightness of such a connection and, if necessary, other shut-off equipment is installed in the system or other design solutions are used. If the technological process allows for small leaks or, for example, the shutdown occurs for a short time, then the use of the system on control valves of this type is quite acceptable.
Shut-off and regulating
Shut-off and control valves occupy an intermediate position between the first two types, combining the advantages of the first and second, which makes them quite versatile.
Interestingly, in Western countries all control valves are divided into 6 classes in such a way that the higher the number, the lower the level of leakage during operation in the closed position. The last 3, according to the traditional Russian classification, are classified as shut-off or shut-off and control valves. To simplify the selection, foreign manufacturers, when supplying products to the Russian market, issue special recommendations for the selection of models, which provide interchangeable analogues, which ensures the ability to meet the necessary conditions for the degree of tightness.
Control and shut-off control valves. Main parameters
The main characteristic of the fittings remains the nominal diameter of its passage. It is equal to the internal one at the inlet and outlet pipes (sometimes these dimensions may be unequal to each other). Each of the values of this conditional diameter corresponds to a certain level of the highest possible flow rate of the transported liquid (also this parameter largely depends on the density of the working medium, the pressure difference and some other parameters).
To simplify the comparison of individual models and carry out technical calculations at the design stage, the term conditional capacity is used. It implies the volume of water under standard conditions (temperature 20 degrees and a difference of 0.1 MPa) that passes through the valve in the open position.
Main design features
The adjustable valve is divided into 3 main parts:
- throttle assembly;
- valve body;
- drive unit.
The first is located inside the valve body itself. The control element consists of a seat and a plunger, which are directly attached to the rod. The saddle itself can have several design options from a design point of view (screwed into the body itself, be integral with it, or pressed with a sleeve).
The plunger moves along the guide, which is located in the cover, and a gasket is installed between the latter and the body to seal it. The valve stem itself is brought out through a special stuffing box assembly, which consists of several spring-loaded fluoroplastic rings. A manual, electric, pneumatic or any other actuator is mounted on the valve cover itself. The latter is combined with the valve stem, and if a non-manual type actuator is used, this makes it easy to include the regulator in an automatic system and control its operation remotely.
The throttle assembly is the main regulating body and shut-off element of the entire system. It is he who ensures the adjustment of the flow area and the parameters of the flow of the working medium.
Specific combinations of bushing-plunger-seat are determined by the following conditions of use:
- type of controlled environment;
- temperature;
- pressure level;
- viscosity;
- the amount of throughput;
- the presence of foreign solid impurities and so on.
Direction of fluid flow.
In the vast majority of cases, for the normal operation of shut-off and control valves, the correct direction of supply of the liquid working medium plays a huge role. It is determined by the arrow marked on the body. If liquid or gas is supplied to the valve in such a way that the working medium is supplied to the plunger from the bottom, then this direction is also called “under the valve”. Otherwise, the supply to shut-off and shut-off valves is often referred to as “to the gate.”
Table 1. Control and shut-off valves. Main technical characteristics
| Parameter name | Meaning |
| Nominal diameter (DN), mm | 15; 20; 25; 32; 40; 50; 65; 80; 100; 150; 200; 250 |
| Conditional pressure (Pu), kgf/cm 2 | 16;25;40;63;100;160;250 |
| from minus 196 to 550 | |
| Ambient temperature depending on climatic version, °C | |
| U | minus 40...+70; 80% at 15°C |
| UHL | minus 60...+70; 80% at 15°C |
| T | minus 10...+85; 80% at 27°C |
Plunger-seat seal |
Metal-metal |
| Metal elastomer | |
| Design of connecting flanges | GOST 12815-80DINANSI for welding |
| Conditional Bandwidth | CM. table 2 |
| Throughput characteristics | Linear, equal percentage, modified |
| Drive unit | |
| Emergency closing/opening time when equipped with a pneumatic drive NO or NC | Pneumatic, manual, electromagnetic, electric (electromechanical) |
Table 2. Conditional capacity of control valves
| Duh, mm |
|||||||||||||||||
| 0,1 | 0,2 | 0,3 | 0,4 | 0,6 | 1,0 | 1,6 | 2,5 | 4,0 | 6,3 | 8,0 | 10,0 | 12,0 | 16,0 | 20,0 | 25,0 | 32,0 | |
| 15 | |||||||||||||||||
| 20 | |||||||||||||||||
| 25 | |||||||||||||||||
| 32 | |||||||||||||||||
| 40 | |||||||||||||||||
| Duh, mm |
Conditional throughput Kvy m 2 /h | ||||||||||||||||||
| 10 | 12 | 16 | 20 | 25 | 32 | 40 | 50 | 63 | 80 | 100 | 125 | 160 | 200 | 250 | 300 | 400 | 500 | 630 | |
| 50 | |||||||||||||||||||
| 65 | |||||||||||||||||||
| 80 | |||||||||||||||||||
| 100 | |||||||||||||||||||
| 150 | |||||||||||||||||||
| 200 | |||||||||||||||||||
Adjustable valves. Actuators (AM)
The shut-off valve actuator with IM is designed to convert the initial control signal directly into the movement of the actuator together with the rod of the shut-off element used. The latter can be a valve, butterfly valve, ball or other element.
Depending on the principle of operation and the type of energy required to impart the required force, actuators for existing control and shut-off valves are divided into the following groups:
- pneumatic;
- electrical;
- hydraulic;
- combined;
- manual.
Pneumatic actuator
IMs based on compressed air, installed on shut-off and control valves, are quite actively used in Russian conditions. This is due to tradition, since the vast majority of industrial automation systems 50-60 years ago were based on the use of compressed air. At the same time, such a regulatory body is highly reliable and repairable, although compared to modern microprocessor-based systems they look somewhat outdated. In addition, controlled flow pneumatic systems are quite large and require installation for compressed air preparation. At the same time, the absence of even a theoretical probability of a spark in the system allows the use of such equipment in explosive areas and dusty workshops.
Depending on the type of drive, all pneumatic actuators are divided into the following groups:
- membrane;
- piston;
- rotary;
- rotating.
Diaphragm actuators
Schematic diagram of a membrane actuator.
1 - regulatory body; 2 - rod; 3 - spring; 4 - membrane; 5 - oil seal
The movement of the output rod, which is connected to the adjustable valve, occurs using the force created by pressure, and the return occurs due to increased spring force. The control signal enters the sealed head, where a membrane with a rigid central part is located. As a result of the action of compressed air pressure, a force is exerted on the membrane, which is equalized by a spring. As a result, the total stroke of the rod is directly determined by the value of the control pressure. The overall stiffness and precompression of the spring form a specific range of forces with a nominal stroke.
Flow control membrane MMs are supplied to the market together with a valve. The peculiarity of the mechanism is the automatic movement of the membrane in the vertical direction, therefore, depending on the design, valves are divided into normally closed (NC) and normally open (NO).
The great advantage of diaphragm actuators for adjustable valves remains their proximity to linear characteristics, which makes adjustment of the flow of the working fluid more accurate. At the same time, in the region of the highest pressure value they have a hysteresis zone ranging from 2-15%. The specific value of the last parameter depends on the effective area of the membrane itself, the parameters of the spring and the pressure drop. To reduce such a zone, an additional power amplifier (positioner) is mounted on the valve IM, which can operate according to a force or displacement compensation circuit.
If it is planned to control the valve using an electrical signal, then special positioners are mounted on the membrane actuators, which convert the received signal into a control air pulse.
Piston pneumatic actuators - similar actuators are installed on adjustable valves in cases where it is necessary to ensure a linear stroke of the rod within 300 mm. To increase overall accuracy and increase real dynamic characteristics, positioners are also used (in this case, the piston drive itself is called a follower).
From a constructive point of view, the entire mechanism is a cylinder, which is mounted on a bracket and a piston with a rod is located. The movement is transmitted to it from the drive and springs, which are oriented relative to the piston in a special way. To increase service life, the inner surface of the cylinder has a special coating to reduce friction.
During operation, the input signal from the control system goes directly to the actuator, which acts on the valve piston. At the same time, the springs create resistance to the increase in pressure from the compressed air, so the overall movement of the rod is determined by the level of rigidity of the installed springs.
Table 4. Main parameters of a piston pneumatic drive
| Piston area, cm 2 | 1250 |
| Type of action | Normally open (NO) |
| Normally closed (H3) | |
| Working environment temperature, °C | from minus 196 to 550 |
| Ambient temperature range, °C and relative average annual humidity, % for climatic version according to GOST 15150: | |
| U | minus 40...+70; 80% at 15°C |
| UHL | minus 60...+70; 80% at 15°C |
| T | minus 10...+85; 80% at 27°C |
| Input signal, MPa (kgf/cm2): | |
| Nominal | 0,02...0,1 (0,2...1,0) |
| Maximum | 0,6 (6) |
| Maximum force required for rotation on the flywheel of the side doubler, kgf | 35 |
The drive is used to control pipeline fittings in cases where torque is required to act on the rod. In fact, such systems can be considered as one of the subtypes of the piston pneumatic type, since the power element is a petal that moves under the supplied compressed air in a special insulated chamber. The movement of a kind of piston is directly transmitted to the drive shaft of the locking element and provides it with the required position.
Additionally, the drive can be equipped with blocks that provide discrete or analog control of shut-off and control valves and have an alarm for the current position of the source shaft. There are also explosion-proof units on the market, which allows them to be installed in dusty and other areas.
The main characteristics of the pneumatic rotary drive are shown in the following table:
Table 5. Main technical characteristics of rotary pneumatic actuators type PPR
| Compressed air pressure for pneumatic drive supply, MPa | 0,25-0,6 |
| Supply air consumption in steady state at an air pressure of 0.6 MPa and an ambient air temperature of 25±15 °C, m 3 /h, no more | 0,5 |
| Time of rotation of the output shaft from one extreme position to another at a load corresponding to the rated torque, s, no more | 3 |
| Climatic performance | U2 according to GOST 15150-69 |
| Ambient air temperature - without additional control and signaling devices, as well as with a pneumatic extreme position indicator | from minus 30 to +70 °C |
| from minus 30 to +100 °C |
Additionally
Other types of actuators
Electric actuators provide control of the entire system using special drives or gearmotors. Their convenience lies in the ability to control them at a large distance, which is convenient for extended systems and minimizes installation costs.
Hydraulic actuators are similar in principle to pneumatic ones, but the difference here is the use of liquid as the working medium. The latter is inconvenient due to the need to ensure proper tightness and purchase hydraulic power stations and other equipment.
Hello, dear reader! In industrial pipelines, through which a huge flow of liquids continuously moves, it is necessary to regulate this movement by reducing or increasing the flow speed and pressure in the pipes. In such cases, it plays an irreplaceable role. In our article we will look at its types and characteristics, connection methods, rules of use, and get acquainted with the advice of specialists on installing and operating the unit.
A shut-off valve with various types of drives is a device with which you can completely or partially block the moving flow of liquid in a pipeline.
The peculiarity of the electric drive design is that it allows these actions to be performed remotely, almost anywhere on the highway.
Purpose and scope of application
Control valves allow you to automatically control at a distance the process of regulating fluid flow and pressure in pipelines.
They are used in large trunk, technological and utility network channels through which the environment is transported.
They can be either shut-off, with the function of only completely blocking the pipe, or with the function of regulating the flow force by completely or partially stopping it.
Controls and technical characteristics
The valve is controlled by the linear movement of the rod with the plunger. The device is started by pressing the start button on the remote control. Under the influence of electric current, the drive transmits force to the plunger. It, moving up and down, changes the cross-sectional area of the passage hole.
The main technical characteristics of shut-off control valves are:
- the value of the nominal pressure in the system that the device can withstand;
- nominal diameter size in mm;
- conditional throughput in m3/h;
- temperature limits at which the unit operates normally;
- network voltage intended for the electric drive.
Connection type
According to the type of connection, shut-off and control devices are divided into
- flanged,
- fittings,
- coupling,
- pin,
- welded
As a rule, valves of this type are already equipped with flanges. They are used in networks with high pressure. Through the flange, the unit can be attached to any pipes of suitable nominal diameter. It also does not depend on what type of device will be connected.
Device
The simplest control valve consists of a body with flanges, in which there is a seat, a rod with a plunger at the end and a sealing unit responsible for sealing all shut-off valves.
When the plunger closes only part of the passage opening, the water flow in the system decreases. A plunger tightly lowered into the seat blocks the flow, the pressure in the pipe after the fittings drops to zero.
If ball valves are used in household pipelines, then in industrial pipelines and utility networks preference is given to spool valves and valves with an electric motor.
Principle of operation
The operating principle of a motorized valve is very similar to that of a conventional valve. They are distinguished by their control method and functionality.
Based on the principle of operation, there are devices that block, mix or divide the main flow.
Shut-off units include two-way saddle valves, which are widely used in municipal heating networks.
For mixing and dividing the flow, having three pipes for connection to the main line.
Types and differences of designs
According to the drive design, valves are divided into controlled ones:
- manually;
- electric drives;
- pneumatic drives;
- electromagnetic way.
According to the locking mechanism, structures are divided into:
- shut-off valves, designed only to shut off the medium;
- membrane, with a rubber membrane in the housing, adapted for operation in gas networks;
- reverse, closing when the flow direction changes;
- spool valve, which regulates the flow intensity by moving the movable spool;
- saddle type, with linear movement of a rod with a plunger, closing or opening the flow path with the help of saddles.
Advantages and disadvantages
The advantages of a pneumatic drive are its affordable price; devices with such controls are cheaper than their electric counterparts.
Valves with an electromagnetic drive greatly facilitate the process of remote control of the environment over a long section of the pipeline and allow the implementation of an electronic control system.
The device itself will be able to take accurate indicators of the condition of the same coolant in pipelines, transmit to the operator information about the pressure level, the amount of liquid in the flow, and even reset the positions of the shut-off parts of the structure.
However, the price and complexity of the devices will increase.
The optimal choice of device should ensure high accuracy in regulation. It is necessary to take into account many factors in order to make the right decision on purchasing a unit.
When selecting fittings, pay attention to:
- product labeling, which indicates the throughput and nominal pressure for the device;
- maintenance conditions for the device, whether it can be repaired without removing it from the line;
- is it possible to change the throughput of the device;
- the presence of structural elements in the device that reduce noise.
Rules for installation and operation of the device
Before installing the device, check the fasteners, the inside of the valve and the main pipes to identify and remove foreign particles. If the need arises, the device is washed and purged.
After installation, check the device for functionality.
During operation, it is necessary to periodically, at least twice a year, inspect the device and carry out routine maintenance.
Check the general condition of the device and its fasteners.
All work on the solenoid valve must be carried out in accordance with the instructions supplied with it.
Required tools and materials
You will need the following set of tools:
screwdriver with appropriate attachments;
- screwdriver;
- pliers;
- flushing hose.
Materials:
- set of bolts;
- copper tubes for wires;
- electrical wire
Connection diagram
Classic two-way control valve installation diagram
Work progress
When installing flanges, make sure that there are no distortions. Do not use excessive force when eliminating misalignment, otherwise the flanges of the device body may be deformed.
During installation, strictly ensure that the arrow on the housing coincides with the direction of flow.
After installation, the device is opened, thoroughly washed and blown.
Check the sealing of the connections and the rod sealing unit.
The functionality of the device is checked by connecting to the electrical network. The valve must operate at full stroke five times without supplying medium. All parts should move easily and without jerking.
Frequent errors and problems during installation
Purchase of a product with an increased nominal bore (DN). Throughput higher than normal will negatively affect the accuracy of regulation.
If you select a valve with a reduced nominal bore, it will not be able to provide the required steam flow at the set pressure. This will lead to the fact that the pressure and temperature of the medium in the pipe after the shut-off device will become lower than the values necessary for the normal functioning of the heating network.
Failure to comply with technology when installing fittings.
These errors can cause instability in the operation of the control system and lead to malfunction of the valve and electric actuator.
In steam pipelines, a condensate trap must be installed in front of the control valves to ensure timely removal of condensate.
During installation, welding should not be carried out on the pipeline with the valve installed, so as not to damage the seals.
Shut-off and control valves are used to control the flow of media at industrial production facilities and household life systems. Trunk pipelines, oil and gas fields and their processing plants, steelmaking and chemical plants, wastewater treatment plants and city water supply are just a small part of the enterprises that require a huge amount of shut-off and control valves.
There are many types and modifications of shut-off and control valves. We will look at the operating principle of the most common product types such as ball valves, butterfly valves, gate valves, gate valves and diaphragm valves.
The operating principle of all the above types of shut-off valves is approximately the same. All these devices either limit the flow of the medium (air, liquids, steam, gas, solids) or completely block it. The only difference is in the design elements of the types of shut-off valves (membrane, disk, ball) with the help of which the flow is blocked.
The ball valve is one of the most reliable elements of shut-off valves. Valves of this type provide a very good possibility of completely shutting off the flow if the shut-off element is turned a quarter turn (90°). The advantages of the ball valve also include low closing time and low probability of leakage in case of seal wear
Ball valves can be divided into partial bore and full bore. A partial bore valve in the open state has a passage diameter smaller than the diameter of the pipeline, a full bore valve has a passage diameter equal to the diameter of the pipeline. A full bore ball valve is more efficient because... allows the pressure drop across the valve to be minimized.
Ball valves are only recommended for use in the fully open or fully closed position. They are not designed for precise flow control, or for operating in a partially open position, as this would create excessive pressure on part of the housing, which could lead to its deformation. Deformation of the housing leads to leaks and breakdowns.
In the "open" position |  |
|---|---|
Step 1 |  |
Step 2 |  |
In the "closed" position |  |
A butterfly valve regulates the flow using a special element - a disk mounted on a shaft and rotating around its axis. Just like a ball valve, a butterfly valve is capable of closing in a fairly short time, since the disk makes the same 90 ° rotation, which is why this valve is also called a quarter-turn.
Depending on the position of the disk and shaft relative to the body, butterfly valves can be three-eccentric or two-eccentric. A valve with offset eccentricity means that the axis of the disk is shifted relative to the geometric axis of the body, which ensures a tighter fit of the disk to the valve seal, and therefore eliminates leaks.
Butterfly valves are characterized by simplicity of design, light weight, and compact dimensions. But the materials used in the manufacture of valves may limit their use in very high temperatures or extremely aggressive environments. This mainly concerns valve seals made of polymer materials.
In the "open" position |  |
|---|---|
Step 1 |  |
Step 2 |  |
In the "Closed" position |  |
The shut-off and control valve is suitable for use in various process facilities, with the exception of large diameter pipelines, to control and regulate the flow of the medium.
The principle of operation of valves is not very different from the principle of operation of other shut-off and control valves. The advantages of these valves are that the valve stroke is short for full opening; accordingly, such a valve usually has small dimensions and an acceptable weight. The valve also has high tightness and no friction between the valve seal and the seat, which significantly reduces their wear.
The disadvantages of this type of valves are strong hydraulic resistance and, accordingly, large energy losses, limitation of the maximum diameter of pipelines on which they can be installed, as well as the existence of stagnant zones (due to the S-shaped internal cross-section) where impurities can accumulate and garbage.
In the "open" position |  |
|---|---|
Step 1 |  |
Step 2 |  |
In the "closed" position |  |
The design of a gate valve resembles a sluice - the flow is regulated by dividing it using a metal plate - a gate. A gate valve is one of the simplest devices for regulating flow.
Gate valves, depending on the design of the locking element, can be wafer-type, double-sided or knife-type.
The advantages of a gate valve include the fact that this type of valve, when open, does not contain any elements that impede the flow.
In the "open" position |  |
|---|---|
Step 1 |  |
Step 2 |  |
In the "closed" position |  |
Diaphragm valves use a flexible membrane (diaphragm) as the shut-off element, a "pinch" method to stop the flow of the valve using the flexible membrane.
One of the advantages of a diaphragm valve is that the components of the valve itself are separated from the medium flow, which in the case of aggressive media increases the service life of the valve, subject to regular maintenance and timely replacement of the membrane.
These types of valves are generally not suitable for aggressive environments and environments with high temperatures; they are mainly used for plumbing systems.
Below is a video that clearly shows the principle of operation of a three-eccentric butterfly valve
Seat control valve (linear)— made on the basis of a seat valve. Regulation is carried out by changing the flow area between the valve and the seat. This type of control valve is called linear because it is controlled by electric actuators with a progressive movement of the stem. The universal design of the control valve allows you to create almost any flow characteristic due to modifications of the valve and seat, and the excellent control characteristics and simple design of the control valve with seat valve have contributed to its widespread use in building engineering systems. The only drawback of linear valves is the complex shape of the flow part, which is unsuitable for use with viscous media.
Ball control valve (rotary)— made on the basis of a ball valve. Regulation is carried out by changing the flow area by rotating the ball around an axis perpendicular to the direction of water flow. The flow section of the ball can be round or another shape. Rotary control valves of this type are called because they are controlled by actuators with radial rotation of the stem. Ball control valves are used in conjunction with high closing force rotary actuators and are controlled by radial movement of the stem. The disadvantages of ball control valves are the need to use expensive electric drives with high closing force and the difficulty of creating a linear or equal percentage flow characteristic - as a result, low control accuracy. The advantages include the simple shape of the flow part, suitable for use with viscous working media.
According to the presence of a protective function, control valves are divided into:
- Normally open - when the power is turned off, the flow area is opened.
- Normally closed - when the power is turned off, they block the flow.
- Without a protective function - when the power is turned off, the electric drive stops.