Working principle and structure of vacuum negative pressure safety valve
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. Several typical structural forms of safety valves. Piston 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.
Ball valve and diaphragm safety valves work in exactly the same way as pistons. 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.
The pilot type safety valve uses 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 maximum opening force is relatively small, that is, the flow characteristics are poor. In practical applications, the type of safety valve should be selected according to actual needs, and the diameter of the safety valve should be selected according to the maximum displacement.