Spring safety valve device. 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 bandwidth 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 influx of medium into the protected vessel or apparatus.
Safety diaphragms (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 rupture, %.
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.
The flanged spring safety valve 17s28nzh is one of the main types that is used to protect pipeline equipment. The spring safety valve 17s28nzh is designed to protect equipment and pipelines from unacceptable excess pressure in the system. Ensuring safe pressure values is carried out by automatically discharging excess working fluid into a specially installed outlet pipeline or into the atmosphere, and when operating pressure is restored, safety valve 17s28nzh stops discharging the working fluid.
The spring safety valve 17s28nzh is mounted with the equipment and using a flange connection. The flanged spring safety valve 17s28nzh has a service life of more than 11 years, and the manufacturer provides a guarantee for it for 18 months from the date the valve is put into operation. Safety valve 17s28nzh is not sealed in relation to the external environment.
Material of the main parts from which the 17s28nzh safety spring valve with flange connection is made:
- Housing, cover - Steel 25L
- Disc, seat - Steel 20Х13
- Rod - Steel 20Х13/Steel 40
- Gasket - AD1M
- Spring - 50HFA
Safety spring valve device 17s28nzh
1 .Cap
2 . Adjustment screw
3 . Spring
4 . Lid
5 . Stock
6 . Manual detonation unit
7 . Spool assembly
8 . Saddle
9 . Frame
Overall and connecting dimensions of safety valve 17s28nzh
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DN, mm |
Dimensions, mm |
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Technical characteristics of safety valve 17s28nzh
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Name |
Meaning |
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Nominal diameter, DN, mm |
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Seat hole diameter dc, mm |
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Allowable leakage in the valve, cm 3 /min |
5-for air 1-for water |
10-for air 2-for water |
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Seat cross-sectional area Fс, mm 2, not less |
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Nominal inlet pressure РN, MPa (kgf/cm2) |
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Nominal outlet pressure РN, MPa (kgf/cm2) |
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Full opening pressure Рп.о. MPa (kgf/cm 2), no more |
For gaseous media: pH+0.05 (0.5) for pH<0,3 МПа; 1,15 Рн для Рн>0.3 MPa For liquid media: pH+0.05 (0.5) for pH<0,2 МПа; 1,25 Рн для Рн>0.2 MPa |
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Closing pressure Рз |
not less than 0.8 pH |
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Spring setting pressure limits, pH MPa (kgf/cm2), not less |
0,05-0,15 (0,5-1,5); 0,15-0,35 (1,5-3,5); 0,35-0,7 (3,5-7,0); 0,7-1,0 (7-10); 1,0-1,6 (10-16) |
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Ambient temperature, °С |
from minus 40 to 40 |
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Working environment temperature, °С |
from minus 40 to 450 |
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Characteristics of the working environment |
Water, steam |
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Flow rate? |
0.8 for gaseous; 0.5 for liquid media |
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Connecting dimensions and dimensions of housing sealing surfaces |
according to GOST 12815-80 version 1 row 2 |
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Weight without flanges (kg) |
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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 excess pressure above 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 of 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 spring safety valve can be used for several maximum permissible 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.
A mandatory element of equipping autonomous water supply systems in dachas and country houses is a check valve. It is such a technical device, which can have different designs, that 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. Referring to direct-acting valves, 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. The most common cause of critical situations is stopping the 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, as well as ensures the correct functioning of the 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 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 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 the regulatory requirements that manufacturers of pumping equipment impose on such devices. The technical parameters by 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 on what technical requirements a water check valve must meet is usually contained in the documentation for the pumping equipment.
To equip domestic water supply systems, spring-type check valves are used; the nominal diameter 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 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. The 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. To manufacture an important element of the locking mechanism - the spring - stainless steel is usually used.
So, if we talk about the structural elements of a 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 a check valve installed in a water supply system works, you should also understand how to choose it correctly. The modern market offers various types of check valve devices, the design, material of manufacture and operation scheme of which can vary significantly.
Sleeve type spring check valveThe 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. The component elements of the housing are connected to each other using a sealing gasket.
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. This 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.
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 pipe for the air vent, with a thread cut on the inner surface, 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 the combined check valve vertically on the pipeline, 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 air pockets from the part of the pipeline that is located before the check valve. That is why, when deciding how to install a combined type check valve, you should clearly understand what functions such a valve should perform.
Spring valves with polypropylene bodyCheck 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 gates of this type is necessary to accommodate the elements of the locking mechanism, which facilitates the maintenance of such a device. Thanks to this design 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.
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 negatively affects the technical condition of the valve itself, and can also cause water hammer to occur 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.
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 get acquainted with the technical characteristics of such a device and compare them with the operating parameters of the pipeline system. The main purpose of a check valve, as mentioned above, is to pass water through the pipeline in the desired direction and prevent the flow of liquid from moving in the opposite direction. 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 a pipeline, you should also keep in mind that you can install a check valve in various ways. On large-diameter pipes, flange and wafer-type check valves are installed, and on small-diameter pipes, coupling valve devices are installed. 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 for a 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 of a 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. 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 task you will need the following materials and tools:
- tee with internal thread, which will serve as a housing;
- 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. (votes: 1 , average rating: 5,00 out of 5)