Selection and installation of safety valve
The safety valve used in pressure equipment, container or pipeline, as the overpressure protection device. When the equipment, container or piping within the pressure exceeds the allowable value, the valve automatically opens, then the whole amount of emissions, to prevent the equipment, container or piping within the pressure continues to rise; when the pressure is reduced to the specified value, the valve should be closed automatically in a timely manner, so as to protect the safe operation of equipment, container or piping.
|Nominal terms||Classification of safety valves|
|Selection of safety valve||How to order safety valve|
System safety valve by valve inlet pressure of the direct drive, in this case is the mechanical load provided by springs or weights to overcome the effect of the bottom of the medium pressure valve. They can also be driven by a body to guide, open or closed by applying a closing force to the valve through the release of the agency or. Therefore, in accordance with the drive mode will be divided into direct acting valve and pilot.
Safety valve opening height in the entire range or in the open within the opening height ratio is quite large, also may open only a tiny proportion of the height range open, then suddenly open to the fully open position. Therefore, can be divided into the proportional valve and the full opening.
To determine the structure, application and public safety valve should be subject to regulations, or should be a statutory authority to agree. Between different specifications, terms of its constraints and the definition may be different. In the application of safety valve, must follow the applicable specifications.
The safety valve is an automatic valve, in the structure and performance parameters and the valves have many differences. Some special terminology easy to confuse, in order to enable users to more clearly understand the safety valve, and correctly use the following terminology to explain some of the main.
- (1) Safety valve: an automatic valve. It does not use any external force, but the use of medium fertility to a nominal amount of fluid discharged to prevent the system pressure exceeds a predetermined safety value; when the pressure returned to normal, the valve closed again, and prevent the media continue to run.
- (2) Direct loading type safety valve. A mechanical load by the direct effect of the safety valve, such as hammer, lever and weight or spring to overcome the medium pressure valve produced by force.
- (3) Assisted safety valve. The safety valve with a power assist device, can open the pressure below the normal open. Even if the auxiliary device failure, the safety valve can still meet the requirements of standard.
- (4) With added load safety valve. This safety valve in the inlet pressure to remain open before the pressure of a sealed pressure increase. The additional force (supplementary load) provided by the external energy, and opening pressure should be achieved reliably release in safety valve. Its size should be set so that the additional force is not released, still in the inlet pressure relief valve opening pressure does not exceed the provisions of state laws and regulations under the premise of the percentage of rated displacement.
- (5) The pilot type safety valve. A safety valve on the media discharged from the pilot valve to drive or control. The pilot valve itself should be directly in line with requirements of the standard load safety valve.
- (6) The proportion of type safety valve. An opening height in the entire range or in the open safety valve to open or close the height range of the considerable proportion.
- (7) Safety valve. Only in a small proportion of open range of opening height, then suddenly open the valve to the full open position. The opening height of not less than 1/4 channel diameter.
- (8) Micro open type safety valve. Is a direct effect only for liquid medium type safety valve. The opening height in 1/40 ~ 1/20 channel diameter range.
- (9) Opening pressure (nominal pressure). Safety valve began to rise in the operating conditions of the inlet pressure, the pressure began to measure the opening height, the media was by visual or auditory continuous emission state of the heavenly stems and earthly branches.
- (10) The discharge pressure. Open the valve to reach the required height of the inlet pressure. The maximum discharge pressure required to follow the relevant national standards or specifications.
- (11) Over pressure. Discharge pressure and opening pressure difference, usually expressed as a percentage of opening pressure.
- (12) The back seat pressure. After the discharge valve with the valve seat again, that turned into a zero height of inlet pressure.
- (13) The opening and closing pressure. The opening pressure and back seat pressure difference, the percentage usually back seat pressure and opening pressure, only when used on low pressure the pressure difference said.
- (14) The back pressure. Safety valve outlet pressure.
- (15) Rated discharge pressure. Standard discharge pressure limit.
- (16) Seal test pressure. To seal the inlet pressure test, measured by the pressure off parts of the sealing surface of the leakage rate.
- (17) Leave the valve closed position of the actual lift.
- (18) The flow area. The valve inlet to the minimum cross-sectional area close to the sealing surface between the channel, without any resistance displacement theory is used to calculate the influence of.
- (19) The channel diameter. For the diameter of flow area.
- (20) Curtain area. When the valve flap in the seat above, in the sealing surface formed between the cylindrical or cone-shaped channel surface area.
- (21) Emission area. The minimum cross-sectional area of the valve when the fluid discharge channel. The Enlightenment of the safety valve, the discharge area equal to the flow area; the micro open type safety valve, the discharge area equal to the area of the curtain.
- (22) The theory of displacement. Is to calculate the displacement of the flow cross-sectional area and valve flow area equal to the ideal nozzle.
- (23) Displacement coefficient. The ratio of the actual displacement and theoretical displacement.
- (24) The discharge coefficient and reduction coefficient (0.9) of the product.
- (25) Rated capacity. Refers to the actual displacement is allowed as part of the safety valve for reference.
- (26) The applicable conditions of pressure, temperature, dielectric properties and other conditions of displacement and rated the same, the calculation of valve displacement.
- (27) Safety valve abnormalities rapidly back and forth movement, the movement of the valve seat contact.
- (28) Safety valve abnormalities rapidly back and forth movement, the movement does not touch the valve seat.
|According to the principle of action||Direct acting||Directly relying on the force generated by the medium pressure to overcome the mechanical load acting on the valve flap to open the valve.|
|Indirect action||Pilot||It consists of a main valve and a pilot valve. The main valve is driven or controlled by the medium discharged from the pilot valve|
|With supplementary load||An additional force to enhance the seal is maintained until the inlet pressure reaches the opening pressure. This additional force should be reliably released when the valve reaches the opening pressure|
|According to the action characteristics||Proportional action||The opening height changes gradually as the pressure increases|
|Both ends acting (bounce action)||The opening process is divided into two stages: at first the valve flap opens proportionally with the increase of pressure. After the pressure rises to a small value, the valve flap is rapidly opened to the specified height when the pressure is almost no longer increased.|
|Press to open height||Micro-open||The opening height is in the range of 1/40~1/20 channel diameter|
|Fully open||Opening height is greater than or equal to 1/4 of the diameter of the runner|
|Zhongqi||Opening height between micro-open and full-open|
|Press with or without back pressure balance mechanism||Back pressure balance||Balance the back pressure with a bellows, piston or diaphragm to balance the action of the back pressure on the upper and lower sides of the valve|
|Conventional||Without back pressure balancing components|
|Press valve loading||Heavy hammer or lever weight||Load directly with a heavy hammer or load with a heavy hammer|
|Spring type||Spring loaded|
|Air chamber||Load with compressed air|
|Applicable conditions||Safety valve type|
|Liquid medium||Proportional active safety valve|
|Gas medium, the necessary emissions are large||Fully open safety valve|
|The required displacement is variable||When the displacement is large, use several safety valves at both ends, the total displacement is equal to the maximum required displacement. When the required displacement is small, the proportional action safety valve is used.|
|The additional back pressure is atmospheric pressure, a fixed value, or a large amount of change (relative to the opening pressure)||Conventional safety valve|
|The additional back pressure is variable and the amount of change is large (relative to the opening pressure)||Back pressure balanced safety valve|
|Require quick response||Direct acting safety valve|
|The required displacement is large, or the caliber and pressure are large, and the sealing requirements are high.||Pilot operated safety valve|
|High sealing requirements, opening pressure and working pressure are very close||Safety valve with supplementary load|
|Mobile or vibrated pressurized equipment||Spring-loaded safety valve|
|Do not allow media to spill into the surrounding environment, or need to recover the displacement of the media||Closed safety valve|
|The medium can be released to the surrounding environment and the medium temperature is high||Open safety valve|
|High medium temperature||Safety valve with heat sink|
The selection of the safety valve is closely related to the system being protected. The selected safety valve should be able to discharge the overpressure medium in the protected system within the specified time to ensure that the pressure in the system is lower than the design pressure of the system. Therefore, the reliability of the safety valve is directly related to the safe and economic operation and personal safety of the protected system.
First, the principle of safety valve setting.
The basic principle of the safety valve setting is for clean, particle-free, low viscosity fluids. When a safety valve must be provided where there are particles, it should be considered to add a filter before the safety valve, provided that the performance of the safety valve is not affected.
Second, the pressure system of one of the following conditions must be installed with a safety valve.
- The pressure material of the container is from the occasion without safety valve.
- Containers and pipes designed to have a pressure less than the pressure source
- The outlet pipe of the volume pump and compressor
- If there is a shut-off valve and a control valve on the outlet pipe of the heating furnace, a safety valve should be installed at the front end.
- The part of the liquid that is thermally expanded due to the closing of the valve at both ends
- Other overpressure parts
Third, the following occasions are not suitable for configuring safety valves
- System pressure may rise rapidly, such as chemical explosions.
- The diarrhea medium contains particles, easy to precipitate, easy to crystallize, easy to polymerize and medium viscosity
- The diarrhea medium is highly corrosive, and the price is too high when using a safety valve
- The working pressure is very low or very high, at this time the safety valve is more difficult to manufacture
- Need a larger area of diarrhea
- The system temperature is low and affects the safety valve operating performance
Fourth, the safety valve and rupture disc should be used in combination in the following cases.
- The medium is very expensive or highly toxic, and there is no leakage in the middle of the work process.
- Increase the discharge area under abnormal conditions (such as fire)
When the user chooses the safety valve, he should first calculate according to the actual working condition, determine the specific model, and order according to the need. When placing an order, at least the following items should be indicated on the order:
- A. Type of safety valve, nominal diameter, runner diameter, connection form of inlet and outlet, pressure level;
- B. Operation pressure and setting pressure of safety valve;
- C. Material of safety valve (material of valve body, inner parts, spring, etc
- D. Standards for manufacturing and acceptance of safety valves.
(2) Special requirements:
- A. Maximum allowable excess pressure;
- B. Necessary displacement and number of valves to be installed;
- C. Physical properties of the medium, the name of the medium used, its weight or molar mass, and component ratio;
- D. Medium working temperature, discharge temperature, etc.
- E. Back pressure of relief valve;
- F. Closed type, wrench, etc.
Source: China Safety Valves Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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