INSTRUCTIONS AND PROPHECIES OF THE Blessed MOTHER ALIPIA GOLOSEEVSKY, Kyiv...
A non-return valve is an element of a pipeline system that provides for the movement of the working medium in only one direction. Its use is mandatory for autonomous pumping stations and other equipment that can fail if the fluid flow moves in the opposite direction.
Check valve spring - one of the varieties of locking elements. It belongs to the category of direct acting valves and operates automatically from the energy of the working environment, which prevents equipment failure in the event of a power outage and other malfunctions.
Design features
The spring valve structurally consists of three elements:
- The body, usually made of brass and equipped with elements for fastening to the pipeline (coupling, thread). The body is also made of steel, cast iron and polypropylene. The choice of material is determined by the parameters of the working environment, the diameter of the pipeline.
- The working element, which is a movable spool, includes two plates with a special sealed gasket between them and a stem.
- An executive body representing a spring located between the plates of the working element and the seat. Provides automatic shutoff of the fluid flow when the pressure drops or changes its direction. The minimum pressure of the working medium at which the valve automatically opens depends on the stiffness of the spring.
Advantages check valves spring:
- possibility of mounting in any position;
- simplicity of design;
- versatility.
At the same time, the valve is sensitive to impurities in the water, which lead to wear of the sealing plates, so it is advisable to install a filter in front of it. It is also recommended to mount the valve in easily accessible places to simplify its operation. Maintenance and replacements.
It is desirable to install the valve in a vertical position so that the blocking force of the spring coincides with the action of gravity. For correct installation it is necessary to focus on the arrow printed on the valve body, which shows the flow direction of the flow of the working medium.
Scope of application
Spring check valves are widely used in systems autonomous water supply, intra-house networks of multi-apartment buildings. They are installed on the suction lines of pumps, in front of storage water heaters, boilers, water meters and other equipment.
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.
All pressure vessels must be fitted with pressure relief devices. For this are used:
lever-cargo PC;
safety devices with collapsing membranes;
Lever-and-cargo PCs are not allowed to be used on mobile vessels.
Schematic diagrams of the main types of PC are shown in Figures 6.1 and 6.2. Weight on lever-load valves (see fig. 6.1,6) must be securely fixed in a predetermined position on the lever after the valve is calibrated. The design of the spring PC (see Fig. 6.1, c) should exclude the possibility of tightening the spring in excess of the established value and provide a device for
Rice. 6.1. Schematic diagrams of the main types safety valves:
checking the correct operation of the valve in working condition by forcibly opening it during operation. The device of the spring safety valve is shown in fig. 6.3. Number of PCs, their dimensions and throughput should be calculated so that in Fig. 6.2. The rupture safety disc did not exceed more than 0.05 MPa for vessels with pressure up to 0.3 MPa,
15% - for vessels with pressure from 0.3 to 6.0 MPa, 10% - for vessels with pressure over 6.0 MPa. When the PC is in operation, it is allowed to exceed the pressure in the vessel by no more than 25%, provided that this excess is provided for by the project and is reflected in the vessel passport.
The bandwidth of the PC is determined according to GOST 12.2.085.
When determining the size of 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 described in the SSBT. For water vapor, the value is calculated by 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 - discharge pipeline;
5 - protected vessel
where bi - coefficient taking into account the physical and chemical 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; the coefficient taking into account the ratio of pressures before and after the safety valve depends on the adiabatic index k and exponent β, for 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 passports of safety valves, for modern designs of low-lift valves α 1 \u003d 0.06-0.07, high-lift valves - α 1 \u003d 0.16-0.17, F- valve passage area, mm 2 ; R 1 - maximum overpressure in front of the valve, MPa;B 1 \u003d 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 - medium temperature in front of the valve at pressure Р b °С.
(6.7)β = (P 2 + 0.1)/(P 1 +0.1), (6.8)
where P2 - maximum overpressure 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 capacity of all installed safety valves must not be less than the maximum possible emergency inflow of medium into the protected vessel or apparatus.
Burst discs (see figures 6.2 and 6.4) are specially loosened devices with a precisely calculated pressure burst threshold. They are simple in design and at the same time provide high reliability of equipment protection. The membranes completely seal the outlet of the protected vessel (before operation), are cheap and easy to manufacture. Their disadvantages include the need to replace after each actuation, the impossibility of accurately determining the actuation pressure of the membrane, which makes it necessary to increase the margin of safety 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 work reliably due to the peculiarities of the influence of the working medium in the vessel (corrosion, crystallization, sticking, freezing). The membranes are also installed in parallel with the PC to increase the throughput of pressure relief systems. The membranes are installed in parallel with the PC to increase the throughput of pressure relief systems. Membranes can be bursting (see Fig. 6.2), breaking, tear-off (Fig. 6.4), shear, snapping out. The thickness of bursting discs A (in mm) is calculated by the formula:
PD/(8σ vr K t )((1+(δ/100))/(1+((δ/100)-1)) 1/2
where D - working diameter; R- membrane actuation pressure, σvr - tensile strength of the membrane material (nickel, copper, aluminum, etc.) in tension; To 1 - temperature coefficient varying from 0.5 to 1.8; δ - relative elongation of the membrane material at break, %.
For tear-off diaphragms, the value that determines the response pressure,
is the diameter D H (see Fig. 6.4), which is calculated as
D n \u003d D (1 + P / σ vr) 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 should be located in places convenient for their maintenance.
Safety devices. Safety devices (valves) must automatically prevent pressure increase beyond the allowable by releasing the working medium into the atmosphere or the disposal system. At least two safety devices are required.
On steam boilers with a pressure of 4 MPa, only impulse safety valves should be installed.
Passage diameter (conditional), mounted on boilers lever-,; cargo and spring valves, must be at least 20 mm. Allowance for this passage to be reduced 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 two valves are installed.
The total capacity of the safety devices installed on steam boilers must be at least the rated capacity of the boiler. Calculation of the capacity of the limiting devices of steam and hot water boilers must be carried out according to 14570 “Safety valves for steam and hot water boilers. Technical requirements".
Places of installation of safety devices are determined. In particular, in hot water boilers, they are installed on the outlet manifolds or on the drum.
The method and frequency of regulation of safety valves (PC) on boilers is indicated in the installation instructions and ex. Valves must protect the vessels from exceeding the pressure in them by more than 10% of the calculated (allowed).
Short answer: All pressure vessels must be fitted with pressure relief devices. For this are used:
spring safety valves (PC);
lever-cargo PC;
pulse safety devices, consisting of a main PC and a direct-acting control pulse valve;
safety devices with collapsing membranes;
other safety devices, the use of which is agreed with the Gosgortekhnadzor of Russia.
Each node of the pipeline system plays an important role in ensuring its performance. For example, a safety spring valve is a pipe fitting that is needed to protect against destruction when excess pressure appears in the pipeline. This is possible by releasing the environment from the system.
Another spring valve ensures the termination of the discharge of the medium when the operating pressure is within the normal range.
Features and principle of operation
The spring-type safety valve is a direct-acting valve that operates from the medium. Where can excess pressure appear in the system? As a rule, the reason lies in external and internal factors:
- incorrectly assembled thermal mechanical circuit;
- heat transfer from sources;
- equipment is not functioning properly.
The spring-loaded safety coupling valve is installed wherever there is a risk of excessive maximum pressure. As a rule, these are household or industrial storage vessels operating under pressure.
The popularity of this armature is provided by a simple design, easy settings, and a range of products. After all, such a variety and possibilities allow you to choose the optimal model for specific conditions.
The safety choke is mounted vertically. The device of a spring-loaded flanged safety valve implies the use of a disk valve as a locking element, which, when locked, is placed between the seats.
The downforce is set using a special tool and a pressure relief valve spring.
When the pressure is very high, the specified downforce is not enough to contain the medium, so the excess is removed until the pressure equalizes to the working level.
The passport for the safety spring valve allows you to find out about the design of the product. The main components are the setter and the locking body. The latter consists of a saddle and a shutter.
It is adjusted by means of a dial so that the spool is properly pressed against the seat to prevent the passage of medium. Adjustment is done with a screw.
The closing pressure of the gate is usually taken below the working one by 10 percent.
Product classification
Consider what types of safety products exist.
By the nature of the lifting of the closing body:
- two-position action;
- proportional action.
According to the height of the organ:
- full-lift;
- medium-lift;
- low-lift.
By type of load on the spool:
- cargo;
- magnetic spring;
- lever-spring;
- spring-.
According to the principle of action:
- direct - traditional safety products;
- indirect action - impulse devices.
One of the modifications widely used in industry is the angular safety spring choke.
Another principle of classification is according to the conditional diameter. For example, if a DN15 spring check valve is used, it means that the nominal diameter is 15 mm, and the DN50 check spring sleeve throttle is 50 mm.
Product characteristics
Throughput calculation is performed in accordance with GOST 12.2.085. The devices can be used in petroleum, chemical, gaseous and liquid media. Tightness is determined according to GOST 9789-75.
The closing pressure of the valve is more than 0.8 Pn, where Pn is the set pressure, which is the highest at the inlet to the valve, at which it remains in the closed state, while maintaining proper tightness.
Springs for them are most often made of steel 50HFA. The spring check valve type 402 is made of cast iron.
In order to check the serviceability of the device in working condition, the SPPK spring-loaded safety valve has a solution for manual opening, purging, therefore, products without SPPK do not have the possibility of manual opening.
The dimensions of the sealing surfaces of the flanges are determined in accordance with GOST 12815-80.
As an example of one of the modifications of the device, we give the fuse 17s28nzh, corresponding to TU3742-017-00218118-2002.
The device has the characteristics:
- working pressure - 1.6 MPa;
- working medium - non-aggressive, gas, steam, water;
- body material - steel;
- sealing material – stainless steel;
- connection - flange;
- temperature - from minus 40 to plus 250 degrees;
- weight and length depend on the nominal diameter.
Nuances of choice
To choose the optimal product, it is necessary to take into account the requirements that apply to them:
- timely and trouble-free installation of a safety valve with a specified increase in the level of working pressure in the system;
- in the open position, the necessary throughput must be provided;
- timely closing of the shutter with the desired level of tightness;
- ensuring stable operation.
Cost is important when choosing. For example, let's consider how much you can buy a safety spring valve 17s28nzh: the price of a reverse clutch spring throttle is from $300.
Of course, a lot depends on the manufacturer. So, a similar Danfoss spring check valve will cost more - from $ 400.
Features of the product (video)
Installation nuances
Before installing a safety spring valve, follow these simple steps:
- check labeling;
- inspect the case for external damage;
- remove the protective cap;
- inside there should not be any foreign objects;
- It should be remembered that during installation, the components of the product will heat up.
The installation process is carried out in accordance with the current safety rules and regulatory and technical standards. The choice of location, design and number of valves, as well as the direction of the discharge of the medium, is determined by the project.
The place must be selected so that free access for maintenance and repair is provided. Installation is carried out in a vertical position at the top of the vessel. Also, the installation can be performed near the vessel or pipeline, only there should not be a shut-off device between the products.
The size of the fitting cannot be less than the diameter of the inlet pipe of the valve.
A poppet spring check valve with a large number of poppets can cause an increase in their resistance, which can change the pressure difference in the top and bottom parts of the product. Therefore, it should be installed in the last area.
Self-installation of such devices is a complex procedure that requires experience and certain skills. Therefore, it is necessary to turn to professionals.
Faults and repairs
The leakage of the medium through the valve occurs when the pressure is lower than the setting pressure.
- delay on the sealing elements of foreign objects - it is necessary to purge the throttle;
- damage to the sealing elements - turning or grinding is performed, followed by a leak test; if the depth of damage is more than 0.1 mm, it is necessary to perform machining;
- spring deformation - it is being replaced;
- misalignment of the elements due to a large load - the load is eliminated, the discharge and intake lines are checked, it is necessary to re-tighten the studs;
- reduced opening pressure - adjustment, deformation of the spring - it is being replaced;
- poor-quality assembly after repair - eliminate all assembly shortcomings.
Repair of safety spring chokes must be trusted to professionals. The cost of the procedure will cost from $50.
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 both as a result of external factors (incorrect operation of equipment, heat transfer from external sources, incorrectly assembled thermal and mechanical circuit, etc.), and as a result of internal physical processes due to some initiating event that is 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 domestic vessels operating under pressure.
Encyclopedic YouTube
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Why a safety valve in a hot water system
Safety valve design (in stereo anaglyph)
Subtitles
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 highly efficient and are used for 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 fitting 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 various problems may arise, such as sticking, freezing, sticking of the spool to the seat. 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
