Spring valve. Safety valve. Types of safety valves

A mandatory element of equipping autonomous water supply systems in dachas and country houses is a check valve. That's exactly what technical device, which may have different design, ensures the movement of liquid through the pipeline in the required direction. Check valves installed in an autonomous water supply system reliably protect it from the consequences of emergency situations. Related to fittings direct action, check valves operate automatically, using the energy of the working medium transported through the pipeline system.

Purpose and principle of operation

The main function that a water check valve performs is that it protects the water supply system from critical flow parameters of the liquid transported through the pipeline. Most common cause critical situations is to stop pumping unit, which can lead to a number of negative phenomena - draining water from the pipeline back into the well, spinning the pump impeller in the opposite direction and, accordingly, breakdown.

The installation of a check valve on the water allows you to protect the water supply system from the listed negative phenomena. In addition, the water check valve prevents the consequences caused by water hammer. The use of check valves in pipeline systems makes their operation more efficient and also ensures correct functioning pumping equipment with which such systems are equipped.

The principle of operation of the check valve is quite simple and is as follows.

The flow of water entering such a device under a certain pressure acts on the locking element and presses the spring, with the help of which this element is kept closed.
After the spring is compressed and the shut-off element is opened, water begins to move freely through the check valve in the required direction.
If the pressure level of the working fluid flow in the pipeline drops or water begins to move in the wrong direction, the spring mechanism of the valve returns the shut-off element to the closed state.

By acting in this way, the check valve prevents the formation of unwanted backflow in the piping system.

When choosing a valve model installed on a water supply system, it is important to know regulatory requirements, which manufacturers of pumping equipment require for such devices. Technical parameters, according to which a check valve for water is selected in accordance with these requirements, are:

working, test and nominal closing pressure;
diameter of the landing part;
conditional capacity;
tightness class.

Information about how technical requirements The check valve for water must correspond, as a rule, contained in the documentation for the pumping equipment.

For equipping water supply systems household use use check valves spring type, the nominal diameter is in the range of 15–50 mm. Despite their compact dimensions, such devices demonstrate high throughput, ensure reliable operation of the pipeline, low level noise and vibration in the pipeline system on which they are installed.

Another positive factor of using check valves in a water supply system is that they help reduce the pressure created by the water pump by 0.25–0.5 Atm. In this regard, a check valve for water allows you to reduce the load both on individual elements of pipeline equipment and on the entire water supply system as a whole.

Design features

One of the most common materials used to make the body of water return valves is brass. Choice of this material is not accidental: this alloy demonstrates exceptionally high resistance to chemically aggressive substances that may be present in water transported through a pipeline in a dissolved or suspended state. Such substances, in particular, include mineral salts, sulfur, oxygen, manganese, iron compounds, etc. The outer surface of the valves, which during their operation is also exposed to negative factors, is often protected with a special coating applied by the galvanic method.

The check valve device requires the presence of a spool, for the manufacture of which brass or durable plastic can also be used. The sealing gasket present in the check valve design can be rubber or silicone. For making important element The locking mechanism - spring - is usually made of stainless steel.

So, if we talk about structural elements spring check valve, then this device consists of:

composite type housings, the elements of which are connected to each other by means of threads;
a locking mechanism, the design of which includes two movable spool plates mounted on a special rod and a sealing gasket;
a spring installed between the spool plates and the seat at the outlet of the through hole.

The principle of operation of a spring check valve is also quite simple.

The flow of water entering the check valve under the required pressure acts on the spool and depresses the spring.
When the spring is compressed, the spool moves along the rod, opening the passage hole and allowing the fluid flow to move freely through the device.
When the pressure of the water flow in the pipeline on which the check valve is installed drops, or in cases when such a flow begins to move in the wrong direction, the spring returns the spool to its seat, closing the throughput hole of the device.

Thus, the operation scheme of the check valve is quite simple, but nevertheless ensures high reliability of such devices and the efficiency of their use in pipeline systems.

Main types

Having understood how the check valve installed in plumbing system, you should also understand how to choose it correctly. On the modern market there are various types check valve devices, the design, material of manufacture and operation scheme of which can vary significantly.

Sleeve type spring check valve

The body of this type of valve consists of two cylindrical elements connected to each other using threads. The locking mechanism includes a plastic rod, upper and lower spool plates. The position of the elements of the locking mechanism in the closed state, as well as their opening at the moment when the pressure of the water flow reaches the required level, is ensured by a spring. Between each other constituent elements the housings are connected using a sealing gasket.

Spring loaded check valve with brass spool and spherical spool chamber

The distinctive features of this type of shutter are easy to see even in the photo. The brass body of such a valve in its middle part, where the spool chamber is located, has a spherical shape. Such design feature allows you to increase the volume of the spool chamber and, accordingly, the throughput of the check valve. The locking mechanism of this type of water valve, which is based on a brass spool, works on the same principle as in any other type of valve device.

Combined spring type check valve with drain and air vent

Many of those who decide to independently install a pipeline system often have a question about why they need a check valve equipped with drainage and air vent systems. The use of check valves of this type (especially for equipping pipelines through which hot working fluids are transported) makes it possible to simplify the process of installation and maintenance of such systems, increase their reliability, reduce the total hydraulic pressure, and reduce the number of installation connections.

On the body of this type of valve, which can be seen even in the photo, there are two pipes, one of which is used for installing an air vent, and the second serves as a drainage element. The branch pipe for the air vent, on the inner surface of which is threaded, is located on the device body above the spool chamber (its receiving part). Such a pipe is needed to bleed air from the pipeline system, for which a Mayevsky valve is additionally used. The purpose of the pipe, which is located on the opposite side of the body - at the outlet of the valve, is to drain the liquid accumulated after the valve device from the system.

If you install a horizontal check valve, its air outlet pipe can be used to mount a pressure gauge. If you place a combined check valve on a pipeline vertically, then its drainage pipe can be used to drain water accumulated after such a device, and the air vent pipe can be used to remove it from the part of the pipeline that is located before the check valve. air jams. That is why, when deciding how to install a check valve combined type, you should clearly understand what functions such a shutter should perform.

Spring valves with polypropylene body

Check valves, the body of which is made of polypropylene, even if you look at the photos of such devices, look very similar to oblique bends. These types of check valves, for installation of which the polyfusion welding method is used, are installed on pipelines also made of polypropylene. An additional oblique outlet in the design of valves of this type is necessary to accommodate the elements of the locking mechanism, which makes it easier maintenance such a device. Thanks to this constructive solution It is not difficult to carry out maintenance and repair of a check valve of this type - it is enough to remove the elements of the locking mechanism from its additional outlet without violating the integrity of the device body and the tightness of its installation in the pipeline system.

Other types of check valves

In pipeline systems designed to transport water, other types of check valves can be installed.

The check valve is equipped with a special shut-off element - a spring-loaded petal. The big disadvantage of valves of this type is that when they operate, significant shock loads are created. This has a negative impact on technical condition the valve itself, and can also cause water hammer in the pipeline system.
Double-leaf check valve devices are compact in size and light in weight.
The lift-off coupling check valve includes a spool as a shut-off element, which moves freely along the vertical axis. The operation of the locking mechanism can be based on the gravitational principle, when the spool returns to the closed state under the influence of its own weight. A spring can also be used for this purpose. If you decide to install a gravity check valve on the pipeline, keep in mind that such a device can only be installed on vertical sections of the system. Meanwhile, the gravity valve is characterized by a simple design, while demonstrating high reliability during operation.
There are check valves whose closing element is a spring-loaded metal ball. The surface of such a ball can be additionally covered with a layer of rubber.

Deciding which check valve is best and whether an expensive valve is needed in the pipeline system is more complex design, you should first get to know technical characteristics such a device and compare them with the operating parameters of the pipeline system. The main purpose of the check valve, as mentioned above, is to pass water through the pipeline in the desired direction and prevent the liquid flow from moving in reverse side. In this regard, you should choose a check valve for water based on the pressure under which the water flow moves in the pipeline. Naturally, it is necessary to take into account the diameter of the pipes on which such a valve should be installed.

When installing the pipeline, you should also keep in mind that you can install a check valve in various ways. On pipes of significant diameter, flanged and check valves are installed. wafer type, and on small-diameter pipes - coupling valve devices. The welded method of installing check valves is used mainly for installation on polypropylene and metal-plastic pipes.

If you choose the right check valve and the method of its installation, such a device will not only last long time, but will also ensure the correct operation of the entire pipeline system.

How to install correctly

Having understood the question of why a check valve is needed and its role in the pipeline system, you should also study the rules for installing it on an already operating or newly created pipeline. Such devices are mounted on various elements of pipeline systems:

on pipelines of autonomous and centralized water supply;
on suction lines served by deep and surface pumps;
in front of boilers, cylinders and water flow meters.

If you are interested in check valves that can be installed in both vertical and horizontal positions, choose spring models rather than gravity ones. You can find out in which direction the water flow should move through the valve by looking at the special arrow marked on the body of the device. When installing coupling-type check valves, be sure to use FUM tape for good sealing. In addition, we should not forget that check valves require regular maintenance, so they must be installed in accessible places in the pipeline.

When installing a check valve on the suction line submersible pump Care should be taken to ensure that a coarse filter is installed in front of such a device, which will prevent mechanical impurities contained in underground water from entering the inside of the device. A perforated or mesh cage can also be used as such a filter, into which a check valve installed at the inlet end of the suction line of a submersible pump is placed.

When installing a check valve on an already operating pipeline, you must first disconnect the system from the water supply and only then install the shutter device.

How to make your own check valve

The simple design of the check valve allows you to make it yourself if necessary.

To solve this problem you will need following materials and tools:

tee with internal thread, which will serve as a body;
a coupling with a thread on the outer surface - the seat of a homemade check valve;
rigid spring made of steel wire;
a steel ball, the diameter of which should be slightly smaller than the diameter of the hole in the tee;
a steel threaded plug that will serve as a stop for the spring;
a standard set of plumbing tools and FUM sealing tape.

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The NEMEN company sells safety valves designed to operate in various environments. We offer, which can be installed vertically on a pipeline section or boiler units.

Purpose of safety valves

A safety valve is a type of fittings that is designed to automatically protect pipelines and equipment from pressure exceeding a certain, predetermined value by releasing excess mass of the working medium. The valve also ensures that venting stops when normal operating pressure is restored. A safety valve is a direct-acting valve that operates directly from the energy of the working medium.

Working principle of safety valve

When the safety valve is in the closed state, the sensitive element of the valve is affected by the force from the operating pressure in the pipeline, which tends to open the valve, as well as the force from the set point preventing the opening. If disturbances occur in the system, causing an increase in the medium pressure above the working pressure, the force of pressing the spool against the seat decreases. When its value is zero, there is a balance between the active forces from the set pointer and the pressure of the medium, simultaneously acting on the valve. If the pressure in the system continues to increase, the shut-off valve opens and the excess medium is discharged through the valve. Reducing the volume of the medium leads to normalization of pressure in the system and the disappearance of disturbing influences. When the pressure level drops below the maximum permissible level, the shut-off element returns to its original position under the influence of force from the setpoint.

Safety spring valves

In such safety valves, spring compression force is used to counteract the pressure of the working medium on the spool. By installing different springs, the same safety spring valve Can be used for multiple maximum allowable pressure settings. Spring valves do not have a stem seal. If the fittings are installed in systems with an aggressive working environment, the spring is isolated using stuffing box devices, an elastic membrane or a bellows. Bellows seals are used in cases where leakage of the working medium from the pipeline is unacceptable.

Safety valves are used in industrial scale and are installed on the main line in order 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).

Device and types 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 safety valves. 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 safety device that prevents a substance from flowing back through a pipeline and releases excess into a low pressure area or atmosphere. This is an indispensable device, as it allows you to save pumps, equipment and the pipeline itself in case of emergency situations.

What types of safety valves are there?

The design of the device is as simple as possible: a locking element and a setpoint that provides power voltage to it. The locking element, in turn, consists of a bolt and a seat.

There are several types of valve:

spring safety valve - the pressure of the working substance is opposed by the force of a compressed spring. The amount of pressure is determined by the compression force, and the range of possible valve settings is determined by the elasticity of the part;
lever - the working substance is restrained using a lever mechanism. Size, pressure and overall range of action are determined by the weight of the load and the length of the lever;
low-lift - the bolt rises only 0.05 of the seat diameter. The opening mechanism is proportional. Such devices are distinguished by their low throughput, low cost and simple structure;
full-lift - the bolt rises to the height of the seat diameter or a little more. The mechanism is two-position. Usually installed on pipelines through which steam or compressed air moves. Stands out for its ability to pass large number working substance and higher cost.

What are the advantages of safety devices?

the most simple structure - guarantees ease and speed of repair and replacement of worn parts;
small size and light weight;
wide price range, which allows you to purchase the product at the most favorable price.

The safety valve allows the pipeline to function efficiently under conditions of high pressure and sudden pressure changes.

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 operation. 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)

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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. The moment this power becomes equal to zero, there is a balance of 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;

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
mid-lift
full lift

By type of load on the spool

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, opening occurs immediately at full speed plates, that's 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 electromagnetic drive, that is, they are not direct-acting fittings. 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