Spring safety valve device. Spring check valve. Purpose of safety valves
All vessels operating under increased pressure must be equipped with safety devices against increased pressure. For this we use:
lever-load PCs;
safety devices with collapsible membranes;
Lever-load PCs are not allowed for use on mobile vessels.
Schematic diagrams of the main types of PCs are shown in Figures 6.1 and 6.2. Weight on lever-weight valves (see fig. 6.1,6) must be securely fixed in the specified position on the lever after calibration of the valve. The design of the spring PC (see Fig. 6.1, c) must exclude the possibility of tightening the spring beyond the established value and provide a device for
Rice. 6.1. Schematic diagrams of the main types safety valves:
checking the proper operation of the valve in working condition by forcing it to open during operation. The design of the spring safety valve is shown in Fig. 6.3. The number of PCs, their sizes and throughput must be calculated so that in Fig. 6.2. The bursting safety membrane did not exceed more than 0.05 MPa for vessels with pressure up to 0.3 MPa, at
15% - for vessels with pressure from 0.3 to 6.0 MPa, by 10% - for vessels with pressure more than 6.0 MPa. When operating PCs, it is allowed to exceed the pressure in the vessel by no more than 25%, provided that this excess is provided for by the design and is reflected in the vessel passport.
PC throughput is determined according to GOST 12.2.085.
When determining the size of the flow sections and the number of safety valves, it is important to calculate the valve capacity per G (in kg/h). It is performed according to the methodology outlined in the SSBT. For water vapor, the value is calculated using the formula:
G=10B 1 B 2 α 1 F(P 1 +0.1)
Rice. 6.3. Spring device
safety valve:
1 - body; 2 - spool; 3 - spring;
4 - outlet pipeline;
5 - protected vessel
Where bi - a coefficient that takes into account the physicochemical properties of water vapor at operating parameters in front of the safety valve; can be determined by expression (6-7); varies from 0.35 to 0.65; coefficient taking into account the pressure ratio in front of and behind the safety valve, depends on the adiabatic index k and indicator β, with β<β кр =(2-(k+1)) k/(k-1) коэффициент B 2 = 1, показатель β вычисляют по фор муле (6.8); коэффициент B 2 varies from 0.62 to 1.00; α 1 - flow coefficient indicated in the safety valve data sheets, for modern designs of low-lift valves α 1 = 0.06-0.07, high-lift valves - α 1 = 0.16-0.17, F- valve flow area, mm 2; R 1 - maximum excess pressure in front of the valve, MPa;B 1 =0.503(2/(k+1) k/(k-1) * 
Where V\ - specific volume of steam in front of the valve at parameters P 1 and T 1, ) m 3 /kg - temperature of the medium in front of the valve at pressure Pb °C.
(6.7)β = (P 2 + 0.1)/(P 1 +0.1), (6.8)
Where P2 - maximum excess pressure behind the valve, MPa.
Adiabatic exponent k depends on the temperature of the water vapor. At a steam temperature of 100 °C k = 1.324, at 200 "C k = 1.310, at 300 °C k= 1.304, at 400 "C k= 1.301, at 500 ° Ck= 1,296.
The total throughput of all installed safety valves must be no less than the maximum possible emergency flow of medium into the protected vessel or apparatus.
Safety membranes (see Figures 6.2 and 6.4) are specially weakened devices with a precisely calculated pressure failure threshold. They are simple in design and at the same time provide high reliability of equipment protection. The membranes completely seal the discharge hole of the protected vessel (before actuation), are cheap and easy to manufacture. Their disadvantages include the need for replacement after each actuation, the inability to accurately determine the actuation pressure of the membrane, which makes it necessary to increase the safety margin of the protected equipment.
Diaphragm safety devices can be installed instead of lever-load and spring safety valves if these valves cannot be used in a particular environment due to their inertia or other reasons. They are also installed in front of the PC in cases where the PC cannot operate reliably due to the peculiarities of the influence of the working environment in the vessel (corrosion, crystallization, sticking, freezing). The membranes are also installed in parallel with the PC to increase the capacity of pressure relief systems. The membranes are also installed in parallel with the PC to increase the throughput of pressure relief systems. Membranes can be bursting (see Fig. 6.2), breaking, tearing (Fig. 6.4), shearing, snapping out. The thickness of bursting discs A (in mm) is calculated by the formula:
P.D./(8σ vr K t )((1+(δ/100))/(1+((δ/100)-1)) 1/2
Where D - working diameter; R- membrane response pressure, σ BP - tensile strength of the membrane material (nickel, copper, aluminum, etc.); TO 1 - temperature coefficient varying from 0.5 to 1.8; δ is the relative elongation of the membrane material at break, %.
For tear-off membranes, the value determining the response pressure is
is the diameter D H (see Fig. 6.4), which is calculated as
D n =D(1+P/σ time) 1/2
It is not allowed to install any shut-off valves between the vessel and the safety device, as well as behind it. In addition, safety devices must be located in places convenient for their maintenance.
Safety devices. Safety devices (valves) must automatically prevent pressure from increasing above the permissible level by releasing the working fluid into the atmosphere or disposal system. At least two safety devices must be installed.
On steam boilers with a pressure of 4 MPa, only pulse safety valves should be installed.
Passage diameter (conditional) installed on lever-type boilers; load and spring valves must be at least 20 mm. The tolerance is to reduce this passage to 15 mm for boilers with a steam capacity of up to 0.2 t/h and a pressure of up to 0.8 MPa when installing two valves.
The total capacity of safety devices installed on steam boilers must be no less than the rated capacity of the boiler. Calculation of the capacity of limiting devices of steam and hot water boilers must be carried out according to 14570 “Safety valves of steam and hot water boilers. Technical requirements".
The installation locations of safety devices are determined. In particular, in hot water boilers they are installed on the outlet manifolds or drum.
The method and frequency of regulation of safety valves on boilers is indicated in the installation instructions and instructions. Valves must protect vessels from exceeding the pressure in them by more than 10% of the calculated (permitted) pressure.
Short answer: All vessels operating under increased pressure must be equipped with safety devices against increased pressure. For this we use:
spring safety valves (SC);
lever-load PCs;
pulse safety devices consisting of a main PC and a direct-acting pulse control valve;
safety devices with rupture membranes;
other safety devices, the use of which has been approved by the Gosgortekhnadzor of Russia.
Safety valves- a type of pipeline fittings designed to protect the heating system from excess pressure. The safety valve is a direct acting valve, i.e. fittings operating directly under the control of the working medium itself (as well as direct-acting pressure regulators).
| Photo Designation | Name | Du, mm | Working pressure (kgf/cm2) | Housing material | Working environment | Connection type | Price, rub | ||
|---|---|---|---|---|---|---|---|---|---|
| 20 | 16 | bronze | water, steam | coupling-pin | 3800 | ||||
| Spring safety valve | 25 | 16 | bronze | water, steam, gas | union-fitting | 12000 | |||
| Low-lift spring safety valve | 15-25 | 16 | steel | ammonia, freon | pin-type | 1200-2000 | |||
| Steel safety valve | 50 | 16 | steel | liquid or gaseous non-aggressive medium, ammonia | flanged | 6660-10800 | |||
| 50-80 | 25 | steel | flanged | 6000 | |||||
| double lever safety valve | 80-125 | 25 | steel | Water, air, steam, ammonia, natural gas, petroleum products | flanged | 9000-19000 | |||
| Full-lift spring safety valve | 25 | 40 | steel | water, air, steam, ammonia, oil, liquid petroleum products | flanged | 20000 | |||
| Angle safety valve | 50-80 | 16 | steel | water, steam, air | flanged | 12500-16000 | |||
| Single lever safety valve | 25-100 | 16 | cast iron | water, steam, gas | flanged | 1500-7000 | |||
| Double lever safety valve | 80-150 | 16 | cast iron | water, steam, gas | flanged | 6000-30000 | |||
| Spring safety valve | 15-25 | 25 | steel | freon, ammonia | union-fitting | 5000-7000 | |||
| Low lift safety valve VALTEC | 15-50 | 16 | brass | water, water vapor, air | coupling | 860-10600 | |||
| Safety valve | 34-52 | 0,7 | steel | water, steam | flanged | 15000 | |||
| Spring safety valve | 50-150 | 16 | steel | flanged | 20200-53800 | ||||
| Spring safety valve | 50-150 | 40 | steel | water, air, steam, ammonia, natural gas, oil, petroleum products | flanged | 20000-53800 | |||
| Spring safety valve | 50-150 | 16 | steel | water, air, steam, ammonia, natural gas, oil, petroleum products | flanged | 20200-53800 | |||
| Angle spring safety valve. | 50 | 100 | steel | gas, water, steam, condensate | flanged | 37900 | |||
| 80 | 100 | steel | gas, water, steam, condensate | flanged | 39450 | ||||
| Spring safety valve with angular damper | 50 | 64 | steel | steam | flanged | 37300 | |||
| Spring safety valve with angular damper. | 80 | 64 | steel | gas, water, steam, condensate | flanged | 46500 | |||
Classification of safety valves:
According to the nature of the elevation of the closing organ:
- proportional action valves (used on incompressible media);
- on/off valves;
According to the height of the lift of the closing organ:
- low-lift (the lifting height of the locking element (spool, plate) does not exceed 1/20 of the seat diameter);
- medium-lift (plate lifting height from 1/20 to ¼ of the saddle diameter);
- full lift (lift height is 1/4 of the saddle diameter or more);
By type of load on the spool:
- spring
- cargo or lever-load
- lever-spring
- magnetic spring
In low-lift and medium-lift valves, the lift of the spool above the seat depends on the pressure of the medium, which is why they are also called valves proportional action. Such valves are mainly used for liquids when large throughput is not required. In full-lift valves, the opening occurs simultaneously, which is why they are also called valves on/off action. Such valves are high-performance and are used for both liquid and gaseous media.
Lever (lever-weight) safety valves, operating principle:
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The principle of operation of a lever-load safety valve is to counteract the force on the spool from the pressure of the working medium - the force from the load transmitted through the lever to the valve stem. The basis of the mechanism of this type of valve is a lever and a load suspended on it. The operation of the device depends on the weight of the load and its location on the lever. The greater the weight and the further it is on the lever, the higher the pressure the valve operates. Lever valves are adjusted to the opening pressure by moving a weight along the lever (the weight of the load may change). Levers are also used to manually purge the valve. Lever valves are prohibited for use on mobile heating devices.
Internal structure of lever safety valve:
1.Inlet; 2. Outlet; 3. Valve seat; 4. Spool; 5. Cargo; 6. Lever.
Sealing of large diameter seats requires heavy weights on long arms, which can cause severe vibration of the device. In these circumstances, valves are used, inside of which the medium discharge cross-section is formed by two seats, which are closed by two spools using two levers with weights (see for example:,). The use of these two-lever valves with two gates, which reduces the weight of the load and the length of the levers, ensuring normal operation of the system.
Adjustment of the lever-weight valve, as noted above, is carried out by moving the weight along the lever. After the required pressure has been adjusted, the load is secured with bolts, covered with a protective casing and locked. This is done to prevent unauthorized changes to the settings. Flanges are often used as weights.
Features of lever-weight valves:
Lever valves are pipeline fittings that were developed before the 40s of the last century. This is an obsolete valve, purchased only to maintain boiler points and similar facilities from the Soviet public utilities era.
A special feature of the valve is the need to grind in the working surfaces (spool and seat - pressed bronze sealing ring) directly at the valve installation site. Lapping means treating the bronze seat with abrasive materials to achieve tighter contact between the spool and the seat. The spool in the valve body is not secured and during transportation and loading its working surfaces are easily damaged. A valve without lapping will not be sealed.
Advantages of lever safety valves:
- Simplicity of design;
- Maintainability;
- Manual adjustment of valve actuation;
Disadvantages of lever safety valves:
- The need to grind in working surfaces;
- Short valve life;
- Bulky design;
Spring safety valves, operating principle:
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The operating principle of a spring safety valve is to counteract the spring force - the force on the spool from the pressure of the working medium (coolant). The coolant exerts pressure on the spring, which compresses. When the set pressure is exceeded, the spool rises and the coolant is discharged through the outlet pipe. After the pressure in the system has dropped to the set pressure, the valve closes and the coolant drainage stops.
Internal structure of spring safety valve:
1 - body; 2 - nozzles; 3 - lower adjusting sleeve; 4, 5 - locking screw; 6, 19, 25, 29 - gasket; 7 - upper adjusting sleeve; 8 - pillow; 9 - spool; 10 - guide sleeve; 11 - special nut; 12 - partition; 13 - cover; 14 - rod; 15 - spring; 16 - support washer; 17 - adjusting screw; 18 - lock nut; 20 - cap; 21 - cam; 22 - guide sleeve; 23 - nut; 24 - plug; 25 - cam shaft; 27 - key; 28 - lever; 30 - ball.
The response pressure of the spring safety valve is set by equipping the valve with various springs. Many valves are manufactured with a special mechanism (lever, fungus, etc.) for manual detonation for control purging of the valve. This is done to check the functionality of the valve, since various problems may arise during operation, such as sticking or freezing of the spool to the seat. However, in industries using aggressive and toxic environments, high temperatures and pressures, control blowing can be very dangerous. Therefore, for spring valves used in such industries, the possibility of manual blowing is not provided and is even prohibited.
When working with aggressive chemical media, the spring is isolated from the working environment using a seal along the rod with a stuffing box, bellows or elastic membrane. Bellows seals are also used in cases where leakage of the medium into the atmosphere is not allowed, for example at nuclear power plants. The maximum operating temperature for safety spring valves is up to +450°C, pressure up to 100 bar.
The relief safety valve opens before the set pressure is reached. The valve opens completely when the pressure exceeds the set pressure by 10-15% (depending on the model). The device closes completely only when the pressure is 10-20% less than the set pressure, because the escaping coolant creates additional dynamic pressure.
If the heating system is functioning stably, without failures or overpressure, the relief safety valve remains without “working” for a long period of time and may become clogged. Therefore, it is recommended to clean it periodically.
Advantages of spring valves :
- simple equipment design;
- small size and weight with large flow sections;
- Possibility of installation in both vertical and horizontal positions;
- possibility of obtaining high throughput.
Disadvantages of spring valves :
- a sharp increase in the spring force when it is compressed during the process of lifting the spool;
- the possibility of receiving a water hammer when closing the valve;
Magnetic spring safety valves, operating principle:
Magnetic spring safety valves use an electromagnetic actuator. The electromagnet provides additional pressing of the spool to the seat. When the response pressure is reached, the electromagnet turns off and only the spring counteracts the pressure, and the valve begins to operate like a regular spring valve. Also, the electromagnet can create an opening force, that is, counteract the spring and force the valve to open. There are valves in which the electromagnetic drive provides both additional pressing and opening force; in this case, the spring serves as a safety net in case of power failure. Magnetic spring valves are commonly used in complex impulse safety devices as control or impulse valves.
Safety valves are used on an industrial scale and are installed on the main line to discharge excess flow of the working medium from the pipeline to reduce the pressure level (a type of household safety valve is the Mayevsky valve, which bleeds air from heating systems).
Design and types of safety valves
The main element of a safety valve is a valve, a rod, adjusting elements, and adjustment springs. By design, safety valves can be lever-load (the working medium presses on the spool, and this pressure is counteracted by the force of the load) and magnetic-spring (actuated by an electromagnetic drive).
Types of safety valves:
- direct action. Triggers when the pressure exceeds the norm;
- indirect action. They are triggered when exposed to an extraneous impulse (for example, from an electric one, used for remote control);
- proportional action. Used in incompressible media;
- two-position action.
Video of safety valve operation
Safety valves can also be low-lift (the lift of the locking part is 1/20 of the diameter of the seat), full-lift (1/4 of the seat, intended for high-capacity highways), and medium-lift. Check valves are a type of safety valve. Safety valves are also divided into shut-off and control valves. The limit pressure is adjusted at the time of installation by changing the position of the adjusting screw that compresses the pressure spring.
- We recommend spring safety valves! Unlike diaphragm valves, they are equipped with additional devices that prevent the spool from freezing to the seat.
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A safety valve is a pipeline fitting that protects high-pressure equipment and pipelines from mechanical damage and various types of destruction as a result of emergency situations. This is achieved by releasing an excess amount of liquid, gas or steam from the system, as well as the vessel in which excessive pressure is formed. In addition, this valve prevents the discharge of the working fluid when the nominal pressure is restored.
A safety valve is a mechanism that operates in direct contact with the working environment together with other structures that perform the function of protective fittings, including pressure regulators.
Main types of valves and their purpose
All safety products may differ from each other in a number of parameters, depending on the design features, namely:
- By type of closing valve:
- proportional;
- two-position.
- According to the lifting height of the closing organ:
- low-lift;
- mid-lift;
- full lift.
- Depending on the type of load on the spool:
- spring;
- lever;
- lever-spring;
- magnetic-spring.
Also, safety valves can differ in the nature of their operation and can be direct or indirect acting devices. The former are considered classic safety mechanisms, while the latter belong to the class of impulse devices. The most commonly used modification in industry is the spring-type corner safety choke.
High pressure (or rather its excess) can occur in the system for various reasons, caused by physical internal processes or other external factors, such as:
Spring type safety valve
Spring-loaded safety valves protect equipment and thereby prevent its destruction as a result of pressure exceeding normal levels. They are used on boilers, various tanks, containers, pipelines and perform the function of relieving the working environment. Excess can be simply released into the atmosphere or into a special discharge pipeline system. After the pressure returns to normal, the valve closes. The main characteristics of a spring safety valve are its flow capacity, as well as its response pressure. The latter is configured on special equipment in the factory, and to test the operation of the device, or to remove dirt that accumulates during operation, the valves have a device that allows you to manually open the device, although some modifications can be done without it. For efficient and reliable operation of the valve in a gaseous environment, its design may include a forced blowing device. In spring-loaded valves, the pressure of the medium on the valve is opposed by the degree of compression of the spring. It is this that determines the actuation force, and the range of adjustments depends on the elasticity of the spring used. This fitting has gained wide popularity due to its simple design, easy settings and wide range of these products. All this allows you to select the most suitable model for use in specific conditions. The safety choke is mounted vertically. The locking element in the spring valve device is a butterfly valve. A special device, along with a spring, sets the clamping force and in the event of excess pressure, the declared clamping force is not enough to hold the medium. As a result, the process of removing its excess from the system occurs until the pressure level is normalized to the original level. You can learn more about the device and design features of a particular spring valve by studying its passport. Its main components are a locking body, consisting of a bolt and a seat, as well as a setter. The setpoint allows you to adjust the valve. It is very important that the spool fits tightly to the seat and prevents leaks. Such adjustments are made using a screw. The valve, as a rule, closes when a pressure appears that is 10% less than the operating pressure.Lever type safety valves
A lever valve is a device in which the shut-off element is sealed using a spring or weight. The purpose of such valves is unchanged - to discharge excess volume of the working medium in case of excessive pressure increase. Adjust the lever valve so that at normal pressure levels, the shutter position always remains closed. The valve spool feels pressure from two forces at once - this can be a load or a spring, as well as the working substance itself. The weight is fixed on the lever arm and its weight is transferred to the valve stem. With predetermined pressure parameters, the force of pressing the valve against the seat must be higher than the pressure force of the working medium and, accordingly, the valve is held in the closed position. As the pressure increases, at a certain moment the clamping force becomes equal to it and it is at this moment that the valve opens. During the period when the valve is open, excess working fluid is drawn in, resulting in a decrease in pressure in the system. After this, the shutter is again pressed against the seat and the valve closes. The vast majority of lever valves are designed as an angular body (the angle of the fittings is 90 degrees). But there are also designs in which the fittings are located on the same axis. This building is called a pass-through. The main purpose of lever valves is to protect against all kinds of emergency situations. In this regard, this type of reinforcement is considered a particularly important critical unit. Like any other product, lever valves must meet certain requirements:- when excess pressure occurs, operation should be carried out quickly and without any complications, and if its indicators decrease to normal, the valve must return to the closed position;
- the throughput of a single valve must be sufficient and equal to the amount of supplied working medium.
With pressure exceeding the established one. The valve must also ensure that the release of the medium ceases when the operating pressure is restored. The safety valve is a fitting direct action, operating directly from the working medium, along with most designs of protective fittings and direct-acting pressure regulators.
Dangerous overpressure can arise in the system both as a result of third-party factors (improper operation of equipment, heat transfer from third-party sources, incorrectly assembled thermo-mechanical circuit, etc.), and as a result of internal physical processes caused by some initial event not provided for by normal exploitation. PC are installed wherever this can happen, that is, on almost any equipment, but they are especially important in the field of operation of industrial and household pressure vessels.
Encyclopedic YouTube
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Why a safety valve in a hot water supply system?
Safety valve design (in stereo anaglyph format)
Subtitles
Operating principle
When the safety valve is closed, a force from working pressure in the protected system, tending to open the valve and the force from the set pointer, preventing the opening. With the occurrence of disturbances in the system, causing an increase in pressure above the operating pressure, the magnitude of the force pressing the spool against the seat decreases. At the moment when this force becomes equal to zero, equilibrium occurs between the active forces from the influence of pressure in the system and the setpoint on the sensitive element of the valve. The shut-off element begins to open, if the pressure in the system does not stop increasing, the working medium is discharged through the valve.
With a decrease in pressure in the protected system caused by the release of the medium, disturbing influences disappear. The shut-off element of the valve closes under the force of the adjuster.
The closing pressure in some cases turns out to be 10-15% lower than the operating pressure, this is due to the fact that to create a tightness of the shut-off valve after operation, a force is required that is significantly greater than that which was sufficient to maintain the tightness of the valve before opening. This is explained by the need to overcome, during landing, the adhesion force of the molecules of the medium passing through the gap between the sealing surfaces of the spool and the seat, to displace this medium. Also, the decrease in pressure is facilitated by the delay in closing the shut-off organ, associated with the impact on it of dynamic forces from the passing flow of the medium, and the presence of friction forces, requiring additional force for its complete closure.
Classification of safety valves
According to the operating principle
- direct acting valves - usually these are the devices that are meant when the phrase is used safety valve, they open directly under the influence of pressure from the working environment;
- indirect-acting valves - valves controlled by using an external source of pressure or electricity, the generally accepted name for such devices is pulsed safety devices;
- proportional action valves (used on incompressible media)
- on/off valves
- low-lift
- mid-lift
- full lift
- cargo or lever-load
- spring
- lever-spring
- magnetic spring
Differences in Designs
Safety valves usually have an angular body, but they can also have a straight body; regardless of this, the valves are installed vertically so that the stem goes down when closing.
Most safety valves are manufactured with one seat in the body, but designs with two seats installed in parallel are also available.
Low-lift safety valves are those in which the lifting height of the locking element (spool, plate) does not exceed 1/20 of the seat diameter; full-lift are valves in which the lifting height is 1/4 of the seat diameter or more. There are also valves with a poppet lift from 1/20 to 1/4, these are usually called mid-lift. In low-lift and medium-lift valves, the lift of the spool above the seat depends on the pressure of the medium, therefore they are conventionally called valves proportional action, although the rise is not proportional to the pressure of the working medium. Such valves are used, as a rule, for liquids when large throughput is not required. In full-lift valves, the opening occurs immediately at the full stroke of the disc, which is why they are called valves on/off action. Such valves are high-performance and are used for both liquid and gaseous media.
The greatest differences in safety valve designs lie in the type of load on the spool.
Spring valves
In them, the pressure of the medium on the spool is counteracted by the compression force of the spring. The same spring valve can be used for different response pressure settings by equipping it with different springs. Many valves are manufactured with a special mechanism (lever, fungus, etc.) for manual detonation for control purging of the valve. This is done to check the functionality of the valve, since various problems may arise during operation, such as sticking, freezing, or sticking of the spool to the seat. However, in some industries under conditions of aggressive and toxic environments, high temperatures and pressures, control blowing can be very dangerous, therefore, for such valves, the possibility of manual blowing is not provided and is even prohibited.
Most often, springs are exposed to the working environment, which is discharged from a pipeline or container when triggered; special spring coatings are used to protect them from mildly aggressive environments. There is no stem seal in these valves. In cases of working with aggressive media in chemical and some other installations, the spring is isolated from the working environment using a seal along the rod with a stuffing box, bellows or elastic membrane. Bellows seals are also used in cases where leakage of the medium into the atmosphere is not allowed, for example at nuclear power plants.
Lever-weight valves
In such valves, the force on the spool from the pressure of the working medium is counteracted by the force from the load, transmitted through the lever to the valve stem. Setting such valves to the opening pressure is done by fixing a load of a certain mass on the lever arm. Levers are also used to manually purge the valve. Such devices are prohibited from being used on mobile vessels.
To seal large-diameter seats, significant masses of weights on long levers are required, which can cause strong vibration of the device; in these cases, housings are used, inside of which the medium discharge cross-section is formed by two parallel seats, which are overlapped by two spools using two levers with weights. Thus, two parallel operating valves are mounted in one body, which makes it possible to reduce the mass of the load and the length of the levers, ensuring normal operation of the valve.
Magnetic spring valves
These devices use an electromagnetic drive, that is, they are not direct-acting valves. The electromagnets in them can provide additional pressing of the spool to the seat, in this case, when the response pressure is reached based on a signal from the sensors, the electromagnet is turned off and only the spring counteracts the pressure, the valve begins to operate like a regular spring one. Also, the electromagnet can create an opening force, that is, counteract the spring and force the valve to open. There are valves in which the electromagnetic drive provides both additional pressing and opening force, in this case the spring serves as a safety net in case of interruption
