Safety valves. Safety valve Purpose of safety fittings

Overpressure. The valve must also be able to stop the discharge of the medium when the operating pressure is restored. The safety valve is a fitting direct action operating directly from the working environment, along with most designs of protective valves and direct-acting pressure regulators.

dangerous overpressure can occur in the system as a result of external factors (incorrect operation of equipment, heat transfer from external sources, incorrectly assembled thermal-mechanical circuit, etc.), and as a result of internal physical processes due to 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 domestic vessels operating under pressure.

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Why a safety valve in a hot water system

Safety valve design (in stereo anaglyph)

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Operating principle

When the safety valve is closed, a force is applied to its sensing element from operating pressure in the protected system, tending to open the valve and the force from the master, preventing the opening. With the occurrence of disturbances in the system, causing an increase in pressure above the working one, the value of the force of pressing the spool to the seat decreases. At the moment when this force becomes equal to zero, an equilibrium of active forces occurs from the pressure in the system and the setting device on the sensitive element of the valve. The shut-off body 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 discharge of the medium, disturbing influences disappear. The shut-off body of the valve closes under the action of force from the setter.

The closing pressure in some cases turns out to be 10-15% lower than the working pressure, this is due to the fact that in order to create the tightness of the shut-off body after actuation, a force is required that is much greater than that which was sufficient to maintain the tightness of the valve before opening. This is explained by the need to overcome the adhesion force of the molecules of the medium passing through the gap between the sealing surfaces of the spool and seat during landing, to displace this medium. Also, a decrease in pressure is facilitated by a delay in closing the shut-off body, associated with the impact on it of dynamic forces from the passing flow of the medium, and the presence of friction forces, requiring additional effort for its complete closure.

Safety valve classification

According to the principle of action

• direct acting valves - usually these devices are meant when they use the phrase safety valve, they open directly under the action of the pressure of the working environment;
• valves of indirect action - valves controlled by using an external source of pressure or electricity, the common name for such devices is impulse safety devices;

• proportional valves (used for incompressible media)
• on/off valves

• low-lift
• medium-lift
• full-lift

• cargo or lever-cargo
• spring
• lever-spring
• magnetic spring

Differences in designs

Safety valves usually have an angle body, but can also have a straight body, regardless of this, the valves are installed vertically so that the stem drops down when closing.

Most safety valves are made with a single seat in the body, but there are designs with two seats installed in parallel.

Low-lift valves are called safety valves, in which the lifting height of the locking element (spool, plate) does not exceed 1/20 of the seat diameter, full-lift valves, in which the lifting height is 1/4 of the seat diameter or more. There are also valves with a poppet height of 1/20 to 1/4, they are usually called medium lift. In low-lift and medium-lift valves, the spool rise above the seat depends on the pressure of the medium, therefore they are conditionally called valves. proportional action, although the rise is not proportional to the pressure of the working medium. These valves are generally used for liquids where a large capacity is not required. In full-lift valves, the opening occurs immediately to the full stroke of the plate, therefore they are called valves. two-position action. These valves are high performance and are used in both liquid and gaseous media.

The biggest differences in the design of safety valves are in the types of loading 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 set pressure settings by equipping with different springs. Many valves are manufactured with a special mechanism (lever, fungus, etc.) for manual blasting for control blowing of the valve. This is done in order to check the operability of the valve, since during operation there may be various problems, for example, sticking, freezing, sticking of the spool to the saddle. However, in some industries in aggressive and toxic environments, high temperatures and pressures, control purge can be very dangerous, so manual purge is not provided for such valves and is even prohibited.

Most often, the springs are exposed to the working medium, which is discharged from the pipeline or tank when triggered; special spring coatings are used to protect against slightly 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 medium by means of a seal along the rod with a stuffing box, bellows or an elastic membrane. The bellows seal is also used in cases where leakage of the medium into the atmosphere is not allowed, for example, at nuclear power plants.

Lever-load 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. The adjustment of such valves to the opening pressure is carried out by fixing a load of a certain mass on the lever arm. Levers are also used to manually purge the valve. Such devices must not be used on mobile vessels.

Sealing large-diameter saddles requires significant masses of weights on long levers, which can cause strong vibration of the device; in these cases, bodies are used, inside which the medium discharge cross section is formed by two parallel saddles, which are blocked by two spools using two levers with weights. Thus, two parallel-operating gates are mounted in one housing, which makes it possible to reduce the weight of the load and the length of the levers, ensuring the 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 by a signal from the sensors, the electromagnet is turned off and only the spring counteracts the pressure, the valve starts to work like a regular spring valve. Also, the electromagnet can create an opening force, that is, oppose the spring and forcibly open the valve. There are valves in which the electromagnetic actuator provides both additional pressing and opening force, in this case the spring serves as a safety net in case of termination

An obligatory element of equipping autonomous water supply systems in dachas and in country houses is check valve. That's exactly what technical device, which can have a different design, ensures the movement of fluid through the pipeline in the required direction. Check valves installed in the system autonomous water supply, reliably protect it from the consequences of emergency situations. Relating to direct acting valves, check valves operate automatically, for which the energy of the working medium transported through the pipeline system is used.

Purpose and principle of operation

The main function that a check valve for water performs is that it protects the water supply system from critical parameters of the flow of 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 into reverse direction and, consequently, breakdown.

Installing a check valve on water allows you to protect the plumbing system from the listed negative phenomena. In addition, the water check valve prevents the consequences that water hammer causes. The use of check valves in pipeline systems makes it possible to make their work more efficient, as well as to ensure the correct functioning of the pumping equipment that such systems are equipped with.

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 depresses the spring, with which this element is held closed.
• After compressing the spring and opening the locking element, 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 the 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 non-return valve prevents the formation of unwanted backflow in the piping system.

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

• operating, trial and nominal closing pressure;
• landing part diameter;
• conditional throughput;
• tightness class.

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

To equip domestic water supply systems, spring-type check valves are used, the diameter of the conditional passage is in the range of 15–50 mm. Despite their compact size, such devices demonstrate high throughput, ensure reliable operation of the pipeline, low noise and vibration levels in the pipeline system on which they are installed.

Another positive factor in the use of check valves in the water supply system is that they help reduce the pressure created by the water pump by 0.25–0.5 atm. In this regard, the 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 from which the body part of the water return valves is made is brass. Choice this material not accidental: this alloy demonstrates an exceptionally high resistance to chemically aggressive substances, which can be in the water transported through the 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, are often protected by a special galvanized coating.

The check valve device assumes the presence of a spool, for the manufacture of which brass or durable plastic can also be used. The sealing gasket present in the design of the check valve can be rubber or silicone. For the manufacture of important element locking mechanism - springs - use, as a rule, stainless steel.

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

• housing of a composite type, the elements of which are interconnected by means of a thread;
• a locking mechanism, the design of which includes two movable spool plates mounted on a special rod, and a sealing gasket;
• spring installed between the spool plates and the seat at the outlet of the through hole.

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

• The flow of water entering the check valve at the required pressure acts on the spool and depresses the spring.
• When the spring is compressed, the spool moves along the stem, opening the orifice and allowing fluid to flow freely through the device.
• When the pressure of the water flow in the pipeline on which the check valve is located, or in cases where such a flow begins to move in the wrong direction, the spring returns the spool to its seat by closing the opening of the device.

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

Main types

Having figured out how the check valve installed in the plumbing system works, you should also understand how to choose it correctly. On the modern market offered different kinds check valve devices, the design, material of manufacture and the scheme of operation of which can vary significantly.

Valve body of this type consists of two cylindrical elements connected to each other by means of a thread. The locking mechanism includes a plastic stem, 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 provided by a spring. Between themselves, the constituent elements of the body are connected using a sealing gasket.

Distinctive features of this type of shutters 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 valve devices of any other type.

Many of those who decide to do the installation of the pipeline system on their own often have the question of why a check valve is needed, 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 field connections.

On the valve body of this type, which can even be seen in the photo, there are two nozzles, one of which is used to mount the air vent, and the second serves as a drainage element. The branch pipe for the air vent, on the inner surface of which a thread is cut, 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 crane is additionally used. The purpose of the branch pipe, which is located on opposite side body - at the outlet of the valve, consists in draining the liquid accumulated after the valve device from the system.

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

Check valves, the body of which is made of polypropylene, even if you look at the photos of such devices, outwardly very much resemble oblique bends. These types of check valves, for the 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 gates of this type is necessary to accommodate the elements of the locking mechanism in it, which facilitates Maintenance such a device. Thereby constructive solution it is not difficult to carry out maintenance and repair of this type of check valve - 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 non-return valves can be installed in pipeline systems designed for transporting water.

• The flap check valve is equipped with a special locking element - a spring-loaded petal. Big disadvantage shutters of this type is that when they are triggered, significant shock loads are created. This negatively affects the technical condition of the gate device itself, and can also cause a hydraulic shock in the pipeline system.
• Double-leaf type check valve devices are compact in size and light in weight.
• The lifting coupling check valve includes a spool freely moving along the vertical axis as a locking element. 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 systems. Meanwhile, the gravity valve is characterized by simple structure, while showing high reliability during operation.
• There are check valves, the locking element of which is a spring-loaded metal ball. The surface of such a ball can be additionally covered with a layer of rubber.

When deciding which check valve is better and whether an expensive valve of a more complex design is needed in the pipeline system, you should first of all get acquainted with technical specifications such a device and compare them with the parameters of the pipeline system. The main purpose of the check valve, as mentioned above, is to pass water through the pipeline in the right direction and prevent the flow of liquid from moving in the opposite direction. In this regard, the check valve for water should be selected 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, it should also be borne in mind that a check valve can be installed different ways. On pipes of significant diameter, check valves of flanged and wafer type, and on pipes of small diameter - coupling gate devices. The welded method of installing check valves is mainly used when mounting on polypropylene and metal-plastic pipes.

If you choose the right check valve and the way it is installed, such a device will not only serve long time, but also ensure the correct operation of the entire pipeline system.

How to install correctly

Having dealt with the question of why a check valve is needed, and with its role in the pipeline system, you should also study the rules for installing it on an already operating or just being 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, storage water heaters and water meters.

If you are interested in check valves that can be installed both vertically and horizontally, choose not gravity, but spring models. You can find out in which direction the water flow should move through the valve using a special arrow printed on the body of the device. When installing sleeve-type check valves, be sure to use FUM tape for good sealing. In addition, one should not forget that check valves need regular maintenance, so they must be installed in accessible places in the pipeline.

When installing a non-return valve on the suction line submersible pump care should be taken to install a coarse filter in front of such a device, which will prevent mechanical impurities contained in underground water from entering the inside of the device. As such a filter, a perforated or mesh cage can also be used, in which a check valve is placed at the inlet end of the suction line of the submersible pump.

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 shut-off device.

How to make a check valve yourself

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

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

• tee with internal thread, which will perform the function of the body;
• a threaded coupling on the outer surface - a homemade check valve seat;
• 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;
• steel threaded plug, which will act as a stop for the spring;
• standard set locksmith tools and sealing FUM tape.
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The safety valve is a safety device that prevents the backflow of the substance through the pipeline and releases its excess into the area low pressure or atmosphere. This is an indispensable device, as it allows you to save pumps, equipment and the pipeline itself in case of emergency.

What are safety valves?

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

There are several types of valves:

• spring-loaded safety valve - the pressure of the working substance is opposed by the force of a compressed spring. The pressure value 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 by a lever mechanism. Size, pressure and overall range are determined by the weight of the load and the length of the lever;
• low-lift - the shutter rises only by 0.05 of the seat diameter. The opening mechanism is proportional. Such devices are distinguished by low bandwidth, low cost and simple structure;
• full-lift - the valve rises to the height of the diameter of the saddle or a little more. The mechanism is two-position. Usually installed on pipelines that move steam or compressed air. Distinguished by its ability to pass a large number of 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 low weight;
• a wide price range, which allows you to purchase the product at the most favorable cost.

The safety valve allows the pipeline to function efficiently under conditions high blood pressure and under extreme pressure conditions.

Spring safety valve (check point)- view pipe fittings, designed to automatically protect equipment and pipelines from excess pressure above a predetermined value by discharging excess working medium and ensuring the termination of discharge at closing pressure and restoration of working pressure.

The main assembly units and parts of the valve:

1 - body, 2 - seat, 3 - spool, 4 - cover, 5 - stem, 6 - nut, 7 - stud, 8 - spring, 9 - bellows (installed in bellows valves), 10 - stop screw, 11 - adjusting sleeve, 12 - guide sleeve, 13 - baffle, 14 - adjusting screw, 15 - cap, 16 - threaded flange.

Principle of operation. At normal operating pressure, the force of the compressed spring presses the spool against the seat (the passage for the discharge of the working medium is closed). When the pressure rises above the set value, an oppositely directed force begins to act on the spool, which compresses the spring, and the spool rises, opening a passage for discharging the working medium. After reducing the pressure in front of the valve to the closing pressure, the spool is again pressed against the seat by the action of the spring, stopping the discharge of the medium.

Mounting position - vertical, cap up.

Shutter tightness- class "B" GOST R 54808. At the request of the customer, it is possible to manufacture with other classes of tightness.

Possible valve designs:

• A sealed cap with a forced opening knot, and without such a knot.
• Balancing bellows.
• Thermal barrier.
• "Open" lid.
• A locking element that prevents the valve from actuating.

Connection to the pipeline:

• flanged;
• under the lens spacer (flange according to GOST 9399);
• choke;
• tsapkovoe.

Bellows valves.

Bellows - a mechanism that compensates for the effect of back pressure at the outlet of the valve. The bellows is designed to protect the valve spring from harmful effects aggressive working environment at high or low temperatures. Bellows valves are made of steel grades 12Kh18N9TL and 12Kh18N12MZTL and are designed for working environments with temperatures from minus 60 °C and below. Designation of bellows valves: KPP4S, KPPS.

The execution of sealing surfaces and connecting dimensions of the valve flanges are in accordance with GOST 12815-80, row 2, construction lengths are in accordance with GOST 16587-71.

Valves DN 25 PN 100 kgf/cm2 can be manufactured with union ends for connection to the pipeline in accordance with GOST 2822-78, as well as with flange connection in accordance with GOST 12815-80, row 2.

Safety valves with a nominal pressure of PN 250 kgf/cm2 and PN 320 kgf/cm2, like other models, are designed to protect equipment from unacceptable overpressure by automatically dumping excess working medium. They are used on equipment with liquid and gaseous working media that do not cause corrosion of body parts more than 0.1 mm.

Safety valves with a stamped body can be manufactured in individual face-to-face lengths (L and L1), heights (H) and connecting dimensions flanges, which allows them to be used as substitutes for imported fittings without changing the already installed equipment and pipelines.

Calculation of valve capacity - according to GOST 12.2.085-2002.

Setting pressure, Рn- the highest excess pressure at the inlet to the safety valve, at which the gate is closed and the specified tightness of the gate is ensured.

Pressure of the beginning of opening, Рн.о.(start pressure; set pressure) - excess pressure at the inlet to the safety valve, at which the force tending to open the valve is balanced by the forces holding the locking element on the seat. At the opening start pressure, the predetermined tightness in the valve gate is violated and the locking element begins to rise.

Pressure full opening, Rp.o.- excess pressure at the inlet to the safety valve, at which the armature moves and the maximum throughput is reached.

Closing pressure, Rz(resetting pressure) is the overpressure at the inlet to the safety valve, at which, after the discharge of the working medium, the locking element is seated on the seat, ensuring the specified tightness of the gate. Valve closing pressure, Рz – not less than 0.8 Рn.

Back pressure- excess pressure at the valve outlet (in particular, from the safety valve).

The back pressure is the sum of the static pressure in the exhaust system (in the case closed system) and the pressure arising from its resistance during the flow of the working medium.

Mandatory minimum order information.

When ordering valves, you must fill out a questionnaire (Appendix B):

• product type, designation, type designation (according to the table of figures);
• nominal diameter of the inlet pipe, DN, mm;
• nominal pressure, PN, kgf/cm2;
• setting pressure (Рн, kgf/cm2) or spring number (if only the spring number is specified, the valve is adjusted to the minimum value from the range of the specified spring);
• case material;
• the presence in the valve design of the manual detonation unit;
• the presence of a bellows valve in the design.

An example of designation when ordering a safety spring valve:

An example of designation when ordering a safety spring valve DN 50 PN 16 kgf/cm2 made of steel 12Kh18N9TL with a manual actuation unit, setting pressure - Pn=16 kgf/cm2, model KPP4R according to TU 3742-005-64164940-2013:

Safety valve KPP4R 50-16 DN 50 PN 16 kgf/cm2, Рn=16 kgf/cm2, 17nzh17nzh. When placing an order, the need to complete the valves with mating parts (counter flanges, gaskets, studs, nuts; for valves DN 25 PN 100 - nipples with union nuts and gaskets) is specifically stipulated.