What is the working principle of hydraulic safety valve?

At present, mass-produced safety valves are available in two types: spring-loaded safety valves and lever-type safety valves. There are also impulse safety valves, pilot safety valves, safety switching valves, safety decompression valves, static and heavy safety valves. The spring-type safety valve mainly relies on the force of the spring. The spring-type safety valve is closed and unclosed. Generally, the flammable, explosive or toxic medium should be closed, steam or inert gas can be used. In the spring-loaded safety valve, there is also a wrench with and without a wrench. The role of the wrench is mainly to check the flexibility of the valve flap, and sometimes it can also be used as a manual emergency pressure relief, as shown in Figure 3. The lever type safety valve mainly relies on the force of the lever weight, but the large size of the lever type safety valve often limits the range of selection. Use a safety valve with a radiator when the temperature is high.

The main parameter of the safety valve is displacement. This displacement is determined by the diameter of the valve seat and the opening height of the valve disc. It is divided into two types: the micro-open type and the full-open type. The micro-open type means that the opening height of the valve flap is 1/40 to l/20 of the throat diameter of the valve seat. Full-open means that the opening height of the valve flap is 1/4 of the throat diameter of the valve seat.

2. Safety valve selection

The operating pressure determines the nominal pressure of the safety valve, and the operating temperature determines the operating temperature range of the safety valve. The calculated constant pressure value of the safety valve determines the constant pressure range of the spring or the lever, and then determines the material of the safety valve according to the medium used. According to the structure type, the throat diameter of the safety valve is calculated according to the relief valve discharge amount. The following are general rules for the selection of safety valves.

(l) Hot water boilers generally use a non-closed wrench with a micro-opening safety valve.
(2) Steam boilers or steam pipes are generally closed with a full-opening safety valve with a wrench.
(3) Liquid incompressible medium such as water generally uses a closed micro-opening safety valve or a safety relief valve.
(4) High-pressure feed water generally uses closed full-open safety valves, such as high-pressure feed water heaters, heat exchangers, etc.
(5) Compressible media such as gas generally use closed full-open safety valves, such as gas storage tanks, gas pipes, and the like.
(6) Class E steam boilers generally use static weight safety valves.
(7) Large-diameter, large-displacement and high-pressure systems generally use pulse-type safety valves, such as temperature-reducing and decompressing devices, power station boilers, etc., as shown in Figure 8.
(8) Built-in safety valves for train tank cars, car tankers, storage tanks, etc. for transporting liquefied gas, as shown in Figure 4.
(9) The top of the tank is generally equipped with a hydraulic safety valve, which is used in conjunction with a breathing valve.
(10) Pilot-type safety valves are generally used for downhole drainage or natural gas pipelines, as shown in Figure 6.
(11) A safety return valve is generally used on the liquid phase return pipe at the outlet of the tank pump of the LPG station.
(12) Vacuum negative pressure relief valves are generally used in systems where negative pressure or negative pressure may occur during operation.
(13) Bellows safety valves are generally used for containers or piping systems where the back pressure fluctuates greatly and is toxic and flammable.

Working principle and structure:
Safety valves provide safety protection in the system. When the system pressure exceeds the specified value, the safety valve is opened, and a part of the gas in the system is discharged into the atmosphere, so that the system pressure does not exceed the allowable value, thereby ensuring that the system does not cause an accident due to excessive pressure. Safety valves are also known as relief valves. The illustration shows several typical structural forms of a safety valve. Figure a is a piston type safety valve, the spool is a flat plate. The air source pressure acts on the piston A. When the pressure exceeds the safe value determined by the spring force, the piston A is opened, and a part of the compressed air is discharged from the valve port into the atmosphere; when the air source pressure is lower than the safe value, the spring is driven. The piston moves down and closes the valve port.

Figures b and c are ball valve and diaphragm safety valves, respectively, operating in exactly the same way as piston. These three safety valves are all springs that provide control and adjust the spring preload to change the safety value. Therefore, it is called a direct-acting safety valve.

Figure d is a pilot-operated safety valve with a small direct-acting valve to provide control pressure on the diaphragm. The hard core on the diaphragm is the valve core and is pressed against the valve seat. When the source pressure A is greater than the safety pressure, the spool opens and compressed air is vented to the atmosphere from the left output orifice. The diaphragm type safety valve and the pilot type safety valve have good pressure characteristics and sensitive action; however, the large opening force of the Zui is relatively small, that is, the flow characteristics are poor. In practical application, the type of safety valve should be selected according to actual needs, and the diameter of the valve should be selected according to the large displacement of zui.

Safety valves provide safety protection in the system. When the system pressure exceeds the specified value, the safety valve is opened, and a part of the gas in the system is discharged into the atmosphere, so that the system pressure does not exceed the allowable value, thereby ensuring that the system does not cause an accident due to excessive pressure. Safety valves are also known as relief valves. The illustration shows several typical structural forms of a safety valve. Figure a is a piston type safety valve, the spool is a flat plate. The air source pressure acts on the piston A. When the pressure exceeds the safe value determined by the spring force, the piston A is opened, and a part of the compressed air is discharged from the valve port into the atmosphere; when the air source pressure is lower than the safe value, the spring is driven. The piston moves down and closes the valve port.

Figures b and c are ball valve and diaphragm safety valves, respectively, operating in exactly the same way as piston. These three safety valves are all springs that provide control and adjust the spring preload to change the safety value. Therefore, it is called a direct-acting safety valve.

Figure d is a pilot-operated safety valve with a small direct-acting valve to provide control pressure on the diaphragm. The hard core on the diaphragm is the valve core and is pressed against the valve seat. When the source pressure A is greater than the safety pressure, the spool opens and compressed air is vented to the atmosphere from the left output orifice. The diaphragm type safety valve and the pilot type safety valve have good pressure characteristics and sensitive action; however, the large opening force of the Zui is relatively small, that is, the flow characteristics are poor. In practical application, the type of safety valve should be selected according to actual needs, and the diameter of the valve should be selected according to the large displacement of zui.