How the safety valve works

When the pressure of the container exceeds the design specification, the safety valve is automatically opened to discharge the high pressure inside the gas reducer to prevent damage to the container or the pipeline. When the pressure in the container drops to the normal operating pressure, it is automatically closed to avoid exhausting all the gas due to overpressure of the container, resulting in waste and production interruption. The safety valve is mainly composed of a valve seat, a valve disc (spool) and a loading mechanism. The valve seat is integral with the valve body, and some are assembled with the valve body, which is in communication with the device.

The valve flap is often attached with a valve stem that snaps onto the valve seat. Above the valve disc is the loading mechanism, the size of the load can be adjusted. When the pressure in the device is within a certain working pressure range, the force acting on the valve disc by the internal medium is less than the force exerted on the valve by the loading mechanism, and the difference between the two forms a sealing force between the valve flap and the valve seat. The valve flap is pressed against the seat and the media of the device cannot be discharged. When the pressure in the device exceeds the specified working pressure and reaches the opening pressure of the safety valve, the force exerted by the internal medium on the valve is greater than the force exerted by the loading mechanism on the valve, so that the valve flap leaves the valve seat and the safety valve opens. The medium inside is discharged through the valve seat. If the displacement of the safety valve is greater than the safety relief of the equipment, the pressure inside the equipment gradually decreases, and after a short period of exhaust, the pressure drops back to the normal working pressure. At this time, the internal pressure acts on the valve flap and the force exerted on the valve is smaller than the force applied by the loading mechanism. The valve flap is pressed against the valve seat, the medium stops discharging, and the device maintains normal working pressure and continues to operate. Therefore, the safety valve is closed or opened by the force of the medium on the valve flap and the force of the loading mechanism to prevent the device from overpressure.

2.Classification

(1) Safety valve for air and other gases (usually represented by type A48Y) according to the medium used for steam (usually A42Y type) Representation) Liquid safety valve (usually represented by type A41H)

(2) Low pressure relief valve according to nominal pressure: Safety valve with nominal pressure PN≤1.6Mpa Medium pressure safety valve: Nominal pressure PN2.5-6.4Mpa safety valve high pressure safety valve: Nominal pressure PN10.0-80.0Mpa safety valve extra high pressure safety valve: nominal pressure PN> 100Mpa safety valve

(3) Temperature sub-low temperature safety valve: safety valve of t ≤ -100 ° C low temperature safety valve: -100 ° C < -40 ° C safety valve. Normal temperature safety valve: -40 °C < ≤ 120 °C safety valve Medium temperature safety valve: 120 ° C 450 ° C safety valve In particular, in view of the actual situation of domestic spring manufacturing, when the safety valve is used above 350 ° C In most cases, the radiator is used or the bonnet is made into a flower basket type, so that the spring can better dissipate heat, so that the spring can always work below 350 ° C to ensure the rigidity of the spring, so as to ensure the correct opening of the safety valve and Back seat and other performance requirements.

(4) Connect the flange to the safety valve according to the connection method. Safety valve inlet and pipe connection flange form, flexible export form. Threaded safety valve. Safety valve inlet and pipe connection thread, flexible export form. Weld the safety valve in succession. Safety valve inlet and pipe connection thread, flexible export form.

(5) According to the structural form, according to the structural characteristics or the ratio of the maximum opening height of the valve flap to the seat diameter (h/d), the safety can generally be divided into the following types: lever weight safety valve. Spring-loaded safety valve. A safety valve that uses the force of the compression spring to balance the pressure of the flap and seal it. See, for example, the A42Y16C safety valve. Pulse safety valve. Pulse safety valves are also known as pilot operated safety valves. It designes the main valve and the auxiliary valve together, and drives the main valve through the pulse action of the auxiliary valve. This type of construction is commonly used in large diameter, large displacement and high pressure systems. Pulse safety valves such as the WFXD type. Micro-open safety valve. The opening height of the valve flap is 1/40∽1/20 of the valve seat diameter, such as A27W-10T and A47H-16C safety valves. Fully open safety valve. Such as A47H-16C safety valve. The opening height of the flap is 1/4 of the valve seat diameter. Fully enclosed safety valve. Such as A47H-16C safety valve. Semi-closed safety valve. Such as A48Y-16C safety valve. Open safety valve. (A48Y-16C safety valve is also open) pilot operated safety valve. Such as WFXD type safety valve.

(6) According to the classification of the seal pair, the cemented carbide is used to seal the carbide. Suitable for high temperature and high pressure applications, especially high temperature and high pressure superheated steam. 2Cr13 pairs 2Cr13r sealing pair. Used in general conditions for saturated steam and superheated steam, or for containers or pipes with temperatures below 450 °C. The seat sealing surface is 2Cr13, and the valve sealing surface is made of cemented carbide. It is used in high pressure steam and other media with a relatively high flow rate and easy to flush the sealing surface. The sealing surface of the valve seat is alloy steel, and the sealing surface of the valve disc is PTFE. Applicable to oil or natural gas media, sealing requirements are strict, but the working temperature is lower than 150 °C. The sealing pair is austenitic stainless steel. The valve body of the safety valve, the valve cover is mostly austenitic stainless steel, and is applied to a medium containing corrosive components such as acid and alkali.

(7) Classify direct-acting safety valves according to the principle of action. Directly relying on the force generated by the medium pressure to overcome the mechanical load acting on the valve flap to open the valve to the safety valve. Pilot operated safety valve. It consists of a main valve and a pilot valve, mainly relying on a safety valve that is driven or controlled by the medium discharged from the pilot valve. With a supplementary load safety method. There is always an additional force to enhance the seal before the inlet pressure reaches the opening pressure, which is a safety valve that is reliably released when the valve opening pressure is reached.

(8) Classification proportional action safety valves according to the action characteristics. A safety valve that opens with a gradual change in pressure as the pressure increases. Two-stage safety valve. (Jump action safety valve). The opening process is divided into twoIn the first stage, at first the valve flap opens proportionally with the increase of the pressure. After the pressure rises to a small value, the valve flap rapidly opens to the safety valve of the specified height when the pressure is almost no longer increased.

(9) Ann opens the highly classified micro-opening security method. Open the safety valve with a height of 1/40-1/20 flowing into the diameter range. Fully open safety valve. Open a safety valve with a height of not less than 1/4 of the flow to the diameter. Zhongkai type safety valve. Open the safety valve between the micro-open and full-open.

(10) With or without back pressure balance mechanism, the back pressure balanced safety valve is classified. The use of a bellows, piston or diaphragm to balance the back pressure of the original, so that the valve open high front back pressure on the upper and lower sides of the valve to balance the safety valve. Conventional safety law. Safety valve without back pressure balance original.

(11) Classification of heavy hammer or lever heavy duty safety valves according to the valve loading method. Use a heavy hammer to load directly or use a heavy hammer to load the safety valve through the lever. Spring-loaded safety valve. Safety valve loaded with compression springs. Air chamber safety valve. Safety valve loaded with compressed air.
(provided by Shenyang Building Materials Network) <


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