Valves are safety spring. Safety valves How to make a check valve yourself
The NEMEN company sells safety valves designed to work in various environments. We offer, which can be installed vertically on a pipeline section or boiler units.
Purpose of safety fittings
A safety valve is a type of fitting that is designed to automatically protect pipelines and equipment from excess pressure in excess of a certain, predetermined value, by dumping excess mass working environment. The valve also provides relief stop when normal operating pressure is restored. The safety valve is a direct-acting valve operating directly from the energy of the working medium.
The principle of operation of the safety valve
When the safety valve is in the closed state, the sensing element of the valve is affected by the force from the working pressure in the pipeline, which tends to open the valve, as well as the force preventing the opening from the setting device. In the event of disturbances in the system that provoke an increase in the pressure of the medium above the working one, the force of pressing the spool to the seat decreases. When its value is equal to zero, there is a balance of active forces from the master and the pressure of the medium, simultaneously acting on the valve. If the pressure in the system continues to increase, the shut-off element opens and the excess medium is discharged through the valve. A decrease in the volume of the medium leads to the normalization of the pressure in the system and the disappearance of disturbing influences. When the pressure level falls below the maximum allowable, the shut-off element returns to its original position under the influence of force from the setpoint.
Safety spring valves
These safety valves use spring force to counteract the pressure of the fluid against the spool. By installing different springs, the same safety spring valve can be used for several maximum allowable pressure settings. AT spring valves stem seal missing. If the valve is installed in systems with aggressive media, the spring is insulated using stuffing boxes, an elastic membrane or a bellows. The bellows seal is used in cases where leakage of the working medium from the pipeline is unacceptable.
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) should automatically prevent the increase in pressure 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.
A safety valve is a safety device that prevents a substance from flowing back through a pipeline and releases excess to 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.
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. They are usually installed on pipelines through which steam or compressed air moves. It is distinguished by the ability to pass a large amount of working substance and a 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 of high pressure and in conditions of sudden pressure drops.
To relieve excess pressure into the atmosphere, safety spring valves are used, which are special pipeline fittings that provide reliable protection of the pipeline from malfunctions and mechanical damage. The device is responsible for the automatic discharge of excess liquids, steam and gas from vessels and systems until the pressure is normalized.
Purpose of the spring valve
Dangerous overpressure in the system occurs as a result of external and internal factors. Both incorrect collection of thermal and mechanical circuits, which causes malfunctions in the operation of equipment, heat entering the system from extraneous sources, and internal physical processes that are not provided for by standard operating conditions that periodically occur in the system, lead to an increase.
Safety products are an indispensable part of any household or industrial pressure system. Installation of safety mechanisms is carried out on pipelines in compressor stations, on autoclaves, in boiler rooms. Valves perform protective functions on pipelines through which not only gaseous, but also liquid substances are transported.
The device and principle of operation of spring valves
The valve consists of a steel body, the lower fitting of which is used as a connecting element between it and the pipeline. If the pressure in the system rises, the medium is discharged through the side fitting. The spring adjusted depending on the pressure in the system ensures that the spool is pressed against the seat. The spring is adjusted by means of a special bushing, which is screwed into the top cover located on the body of the device. The cap located in the upper part is designed to protect the bushing from destruction as a result of mechanical influences. The presence of a special lug for sealing allows you to protect the system from outside interference.
For valves in which a spring acts as a balancing mechanism, the force of the working body is selected. If the parameters are chosen correctly, in the normal state of the system, the spool, which is responsible for releasing excess pressure from the pipeline, should be pressed against the seat. When the performance increases to a critical level, depending on the type of spring device, the spool moves up to a certain height.
The safety spring valve, which provides timely pressure relief, is made of different materials:
- Carbon steel. Such devices are suitable for systems in which the pressure is in the range of 0.1-70 MPa.
- Stainless steel. Valves made of stainless steel are designed for systems, the pressure in which does not exceed 0.25-2.3 MPa.
Classification and characteristics of spring valves
The safety spring valve is available in three versions:
- Low lift devices suitable for gas pipeline and steam pipeline systems, the pressure in which does not exceed 0.6 MPa. The lift height of such a valve does not exceed 1/20 of the seat diameter.
- Medium lifting devices, in which the spool lift height is from 1/6 to 1/10 of the nozzle diameter.
- Full lift devices, in which the valve lift reaches up to ¼ of the seat diameter.
Known classification of valves based on the way they open:
- Check spring valve. To control the check spring valves, an indirect external pressure source is involved. Spring check valves, which are called impulse safety devices, can be operated by the action of electricity.
- Straight valve. In direct type devices, the working pressure of the medium has a direct effect on the spool, which rises with increasing pressure.
Allocate open valves and closed type. In the case of a direct type device, when the valve is opened, the medium is discharged directly to the atmosphere. Closed type valves remain completely sealed to the environment by relieving pressure in a dedicated piping.
Advantages
There are various types of equipment that provide relief of excess pressure from the system, but spring safety valves are popular due to the presence of important advantages:
- Simplicity and reliability of a design.
- Ease of setting the operating parameters and ease of installation.
- Variety of sizes, types and designs.
- Installation of a safety product is possible both in horizontal, and in vertical position.
- Relatively small overall dimensions.
- Large cross section.
The disadvantages of safety valves include the presence of limitations in the lift height of the spool, increased requirements for the quality of manufacturing of the spring for safety valves, which can fail when operating in an aggressive environment or constant exposure to high temperatures.
How to choose a spring valve?
When choosing a fuse, it is worth relying on several important principles, the consideration of which depends on the uninterrupted operation of the system and the ability of the fuse to perform the necessary functions:
- Spring loaded safety valves are the smallest in size compared to other types of safety relief valves, so they should be selected when space is not available.
- Features of the use of valves are associated with the presence of increased vibrations, which adversely affect the performance of the device and can quickly render it unusable. For example, lever-type devices are more prone to breakage due to vibration due to the presence of a long lever with weight and hinges in the design. Therefore, for systems in which significant vibration effects are observed, it is worth choosing a safety spring valve.
- Depending on the design features of the device, the spring can change the pressure force over time. This is due to the fact that the constant rise of the spool causes changes in the structure of the metal.
Installation nuances
A spring-type safety valve is installed at any point in the system that is subjected to increased pressure and is at risk of mechanical damage. The device does not require a large free space, which is a significant advantage compared to other types of safety devices.
In order to avoid malfunctions, no shut-off valves should be installed upstream of the safety valve. To discharge the gaseous medium, special devices are installed or the discharge occurs directly into the atmosphere. To alert personnel, along with spring valves, a special whistle is mounted, which is placed on the discharge pipe. When the valve is actuated, a whistle will sound to indicate that the system has been pressurized and the valve has opened to release media.
Possible causes of safety valve failures
Safety valves are robust and reliable devices that provide permanent protection of systems against overpressure. A direct or check spring valve fails for several reasons:
- The presence of increased vibrations;
- Constant exposure to aggressive media on the safety throttle.
- Incorrect installation of the safety spring throttle or valve.
In order to avoid accidents and malfunctions in the functioning of systems, safety valves are periodically checked for malfunctions. Valves are tested for strength and tightness before being put into service. Periodic checks are also carried out to determine the tightness of sealing surfaces and stuffing box connections.
With the right choice of safety devices, taking into account the parameters of the system, carrying out periodic checks and timely troubleshooting, safety spring valves will ensure reliable operation of the system and trouble-free protection against overpressure for a long time.
The safety valve is a pipeline fitting that protects high-pressure equipment and pipelines from mechanical damage and various kinds of damage as a result of emergency situations. This is achieved by venting excess liquid, gas or vapor from the system, as well as vessels in which excessive pressure is formed. In addition, this valve prevents the discharge of the working medium when the nominal pressure is restored.
A safety valve is a mechanism that operates in direct contact with the working medium, together with other structures that perform the function of protective fittings, including pressure regulators.
The main types of valves and their purpose
All safety products may differ from each other in a number of parameters, depending on the design features, namely:
- Closing valve type:
- proportional;
- on-off.
- According to the lifting height of the closing body:
- low-lift;
- medium-lift;
- full-lift.
- Depending on the type of load on the spool:
- spring;
- lever;
- lever-spring;
- magnetic spring.
Also, safety valves may differ in the nature of their work and be direct or indirect acting devices. The former are considered classic safety mechanisms, while the latter belong to the class of impulse devices. The most commonly used modification in the industry is the spring type angular safety choke.
High pressure (or rather, its excess) can occur in the system for various reasons caused by physical internal processes or other external factors, such as:
Spring Type Relief Valve
Spring-loaded safety valves protect the equipment, and thereby prevent its destruction, as a result of exceeding the pressure above the norm. They are used on boilers, various tanks, tanks, pipelines and perform the function of dumping the working medium. The surplus can simply be discharged into the atmosphere or into a special discharge pipeline system. After the pressure returns to normal, the valve closes. The main characteristics of a safety spring valve are its flow capacity, as well as the value of the set pressure. The latter is configured on special equipment at the factory, and to test the operation of the device, or to remove dirt that accumulates during operation, the valves have a device that allows you to manually open this device, although some modifications can do without it. For efficient and reliable operation of the valve in a gaseous medium, a forced airflow device may be present in its design. In spring valves, the pressure of the medium on the gate is opposed by the degree of compression of the spring. It is she who determines the actuation force, and the range of adjustments depends on the elasticity of the spring used. This fitting has gained wide popularity due to its simple design, easy settings and a wide range of these products. All this allows you to select the most suitable model for operation in specific conditions. The safety choke is mounted vertically. The locking element in the spring valve device is a butterfly valve. A special device, along with a spring, sets the clamping force and in case of excessive pressure, the declared clamping force is not enough to hold the medium. As a result, the process of removing its excess from the system takes place until the pressure level is normalized to the initial level. You can learn more about the device and design features of a particular spring valve by examining its passport. Its main components are the locking body, consisting of a valve and a seat, as well as a setter. The adjuster allows you to adjust the valve. It is very important that the spool fits snugly against the seat and prevents leakage. These adjustments are made with a screw. The shutter, as a rule, closes when a pressure appears, which is less than the working one by 10%.Lever Type Safety Valves
A lever valve is a device in which the shut-off element is sealed with a spring or load. The purpose of such valves is invariably - the discharge of excess volume of the working medium in the event of an excessive increase in pressure. Adjust the lever valve so that at normal pressure readings, the valve always remains in the closed position. The valve spool feels the pressure of two forces at once - it can be a load or a spring, as well as directly the working substance. The load is fixed on the arm of the lever and its weight is transferred to the valve stem. At predetermined pressure parameters, the force of pressing the valve to the seat must be higher than the pressure force of the working medium and, accordingly, the valve is held in the closed position. With increasing pressure, at a certain moment the downforce becomes equivalent to it and it is at this moment that the valve opens. During the period when the valve is open, the excess working medium is taken in, as a result of which the pressure in the system decreases. After that, the valve is again pressed against the seat and the valve closes. The vast majority of lever valves are made in the form of an angular body (the angle of the fittings is 90 degrees). But there are also such designs in which the fittings are located on the same axis. This body is called a passage. The main purpose of lever valves is to protect against all kinds of emergencies. In this regard, this type of reinforcement is considered a particularly important critical node. Like any other product, lever valves must meet certain requirements:- operation in the event of excessive pressure should be carried out quickly and without any complications, and when its performance drops to normal, the valve must return to the closed position;
- the flow capacity of a single valve must be sufficient and equivalent to the amount of the supplied working medium.
We also recommend
How to make a healthy banana smoothie
Harvesting asparagus for the winter recipes for cooking at home
Chicken pie with zucchini and cottage cheese Dukan's recipes zucchini pie with cottage cheese
Gingerbread with icing
How to cook a salad with crab sticks and carrots
Cabbage salad with bell pepper - the best recipes
Loading...