Analysis of Safety Valve Technology

Analysis of Safety Valve Technology

Safety valves are safety devices that are widely used in pressure systems. When the pressure in the pressure system exceeds the specified value , the safety valve opens automatically. When the medium pressure drops to a certain value , the safety valve returns to the seat and closes automatically. Direct acting safety valves are basically divided into spring type and heavy hammer type. A wide range of current application is a spring-loaded safety valve, when the operating state, which provides a sealing force of the spring, to ensure the normal operation of the device. When the pressure rises , the medium pressure overcomes the spring force to open the valve and the system pressure drops . When the pressure drops to a certain value , the valve will return to the seat under the action of the spring force. In the hydrogen-oxygen system of the test stand , since hydrogen and oxygen are all low-temperature media , in order to reduce the loss of the media and better adiabatic cooling , a full-open safety valve ( including a pilot-operated safety valve ) is used to reduce the opening size and reduce heat leakage. .

The key to the safety valve design is the spring design and the sealing surface design. The spring not only affects the seal , but also the sensitivity of the valve , and the design of the sealing surface structure and material will directly affect the sealing of the valve.

spring

The spring element is operating at higher stress, the surface of the material by the force, the spring and the mechanical properties of the material a greater impact on the surface quality of the spring. The amount of spring material is more spring steel, followed by a nickel alloy, high elastic alloy and stainless steel, the test cell relates to test systems because most low-temperature conditions, so most of the spring material selected 50CrVA, 60Si2MnA, 1Cr18Ni9Ti, 0Cr18Ni9 and QBe2 Wait. Including 1Cr18Ni9Ti ( Material Standard Number DGB09 - 1989)

When the spring and the safety valve are not suitable , the valve cannot work normally. Because if the spring is too hard , the system pressure will rise too high when the valve is opened , making the device unable to operate safely. If the spring is too soft , the seat back pressure of the valve will be greatly reduced , making the device a waste of large amounts of media. In industrial production, in order to obtain the discharge pressure and the back seat requirements, the design in general, the method of the adjusting ring, but the valve hydroxide test system do not take this approach because of the danger of such a medium to determine its Emissions should be made at the prescribed location , and the presence of the adjustment ring causes the valve to leak into the atmosphere during discharge.

Sealing pair

The material of the safety valve closing part should have corrosion resistance, corrosion resistance, pressure resistance, good machinability, and good elastic deformation ability . Among them, erosion resistance is the first consideration in material selection , and erosion is the medium to the metal surface. The result of a combination of mechanical wear and corrosion. The low temperature resistance of the material in the test stand system is also a major consideration , so stainless steel (0Cr18Ni9) is used as the main material of the valve. Sealing materials are stainless steel (0Cr18Ni9) - brass, stainless steel (0Cr18Ni9) - aluminum, stainless steel (0Cr18Ni9) - Teflon, stainless steel (0Cr18Ni9) - reinforced Teflon and stainless steel (0Cr18Ni9) - polyimide Wait.

When designing a valve , increasing the specific pressure on the sealing surface is a frequently used method. However , according to the requirements of the standard , the opening pressure of the safety valve is ps = (1105 to 111) p. This requirement makes the force acting on the sealing surface a fixed value , and the specific pressure on the sealing surface is selected when the width of the sealing surface is selected . Its value has also become a constant value , and it is usually impossible to maintain a reliable seal of the sealing mechanism. Therefore, the tightness of the safety valve depends to a large extent on the structure of the valve and the precision of manufacture and assembly. In addition to the safety valve operation state leakage than the sealing surface and down about, but also the sealing surface is subject to mechanical damage, the valve flap neutral force changes, the temperature of the surrounding medium due to the sealing surface and the sealing surface being deformable medium Contamination of impurities and other factors. In order to reduce the leakage of the valve, it is necessary to increase the requirements in terms of structure, manufacture and assembly, and in particular, the surface quality and geometrical position tolerance of the sealing surface must be taken into account. Reasonably select the width and structure type of the sealing surface , try to make the calculated specific pressure value similar to the small sealing ratio , so as to ensure the sealing performance of the valve.