Operation principle of safety valve-1

Release time:

2024-05-14

The safety valve is an automatic valve. When the medium pressure in the safety valve exceeds the specified value, it will open automatically; when the medium pressure decreases to another limited value, it will close automatically. Figure 2-1 is a schematic diagram of the safety valve that uses the spiral compression spring to generate the external closing force. When the valve is installed on the pressure vessel and the protected system is at working pressure, the safety valve is closed (sealed)

At this time, the spring force P1 acting on the disc is:

P1 ＝pA 十 F0

P1 = PA ten F0

式中：P― 介质压力，MP ；

Where: P - medium pressure, mp;

A - effective pressure area on valve disc, cm2;

F0-mp is the downward additional force to compress the disc and seat.

The pressing force F0 of the disc on the sealing surface of the valve seat has actually formed the force and reaction force, which is calculated by the unit sealing area, called the specific pressure, also called the specific pressure of the seal. As long as the specific pressure is large enough, it can ensure that the valve closure parts achieve the necessary tightness. When the medium pressure in the protected system increases and exceeds the calculated working pressure, the compression force will decrease accordingly. When the specific pressure is small to a certain extent, the medium begins to penetrate the sealing surface of the valve disc and the valve seat, forming a small gap between the sealing surface, and then local leakage will occur, and the intermittent leakage will gradually form a continuous leakage. With the further increase of medium pressure, the valve disc is lifted up out of the valve seat, and then discharged. When the medium pressure is at the normal working pressure, the valve is closed again under the action of spring force P1, that is, the safety valve is reseated. In each stage of the action process of the safety valve, the relationship between the pressure value and the normal working pressure of the vessel, "maximum allowable working pressure" refers to the maximum allowable pressure of the pressure vessel determined by the effective thickness of the pressure vessel, which may exceed the design pressure of the vessel. In order to ensure the safety of the operating equipment, the setting pressure of the safety valve shall not be greater than the design pressure of the pressure vessel, because the design pressure of the vessel is taken as the starting pressure of the overpressure limit. Only in case of special needs, the maximum allowable working pressure of the pressure vessel is taken as the starting pressure of the overpressure limit of the equipment. In normal operation, the safety valve

In the sealed state, the sealing test pressure of the safety valve shall be higher than the normal operating pressure of the pressure vessel.

For the mobile pressure vessel, in order to prevent the frequent action of the relief device and the leakage. The opening pressure of safety valve shall be 1.05-1.10 times of the tank design pressure, which is different from that of fixed pressure vessel.

According to the action principle, the safety valve can be divided into two types: one is the proportional action micro open safety valve mainly used for liquid, the other is the two-stage action full open safety valve used for gas or steam. When the pressure in front of the valve changes, the action process and performance of the two types of safety valves are different

一、比例作用徽启式安全阀

I. proportional action swing safety valve

The proportional micro lift safety valve, also known as the micro lift safety valve, is opened with the increase of the medium pressure in the container. In this type of safety valve, the opening height of the valve disc is generally only 1 / 20-1 / 40 of the valve seat diameter because there is no special mechanism to assist in increasing the opening height. The sectional area of the displacement is the annular gap formed between the valve disc and the valve seat. Micro opening safety valve is mainly used for liquid medium. Because the opening and closing process is relatively stable, it will not cause great fluctuation of liquid pressure in the protected system, which is suitable for the pressure vessel filled with liquid.

The other feature of the micro opening safety valve is that it can also be used on the equipment which needs to discharge less gas, such as small air compressor, evaporator and small boiler.