Knowledge

What is a pilot safety valve?



The guide of safety valve: pilot safety valve (also called pulse type safety valve), is a safety valve that relies on the discharge medium from the guide valve to drive or control the main valve, and the guide valve itself is a standard spring load type safety valve. The safety valve is a type of automatic valve, which is mainly used in boiler, pressure vessel and pipe. The control pressure does not exceed the specified value. It plays an important role in protecting the safety of the human body and the operation of the equipment. According to the safety valve opening height, it can be divided into a micro start safety valve and a full open safety valve.

Guide type safety valve classification: lead type safety valves are divided into vertical, lever, spring and pilot (pulse type). According to the body structure, it can be divided into two types: closed and non closed. The closed safety valve, which excludes the medium, does not leak, and it is all excreted along the outlet to the designated place, which is usually used in toxic and corrosive media. For air and steam safety valve, the use of non closed safety valve. For the selection of safety valve products, it should be determined according to the actual seal pressure. For spring safety valves, in a range of nominal pressure (PN), a spring with several working pressure levels, in addition to the type, name, medium and temperature of the safety valve, should be marked, otherwise the seal pressure of the valve body should be marked, otherwise the pressure should be supplied according to the special pressure.

Pilot safety valve features: pilot safety valve is suitable for occasions with high pressure and large caliber. The pilot safety valve has good sealing performance, and its action is seldom affected by back pressure. The disadvantage of this kind of safety valve is that its reliability is related to the main valve and guide valve, and the action is not as fast and reliable as the direct action type safety valve, and the structure is more complex.

The working principle of pilot operated safety valve is when the protected system is in normal operation. The slide valve in the valve cavity is in the open state. The system pressure is imported through the main valve through the lower pipe, the guide valve cavity and the upper tube into the main valve valve (piston) valve. At this time, the gas pressure of the upper gas chamber is equal to the system pressure of the main valve inlet. The sealing surface of the pilot valve is in a sealed state, so that the gas in the gas chamber above the main valve can not be discharged from the outlet of the pilot valve. Because the piston area is larger than the area of the disc seal surface, the system pressure produces a downward resultant force on the main valve flap, so that the main valve is closed and sealed.

When the pressure of the system is raised to the setting pressure, the gas is up to the top of the guide valve in the seal face of the guide valve, so that the cover is in the open state, and the slide valve in the valve cavity moves upwards, and the air passageway is closed in the valve cavity of the guide valve. The medium of the upper chamber of the main valve is discharged through the open guide valve sealing surface, so that the pressure on the upper side of the main valve is reduced. The main valve disc opens under the pressure of the inlet and releases the pressure of the system.

When the pressure of the system is reduced to a certain value, the valve valve core is down back to the seat under the action of the spring, the guide valve seal face is closed, the slide valve of the guide valve cavity opens, the valve cavity is unblocked, and the system pressure is passed through the valve cavity of the guide valve again to the upper valve valve chamber of the main valve, and the main valve disc is closed to [1].

Caution: all kinds of safety valves should be installed vertically.

At the outlet of the safety valve, there should be no resistance to avoid pressure.

The safety valve shall be specially tested before installation and its sealing performance shall be checked.

The safety valve in use should be checked regularly.

Installation requirements

(1) a boiler with a rated evaporation greater than 0.5t/h, at least two safety valves: a boiler with a rated evaporation less than or equal to 0.5t/h, at least one safety valve. Safety valves must be installed at the outlet of the separable economizer and the outlet of the steam superheater.

(2) the safety valve should be installed vertically in the special position of the pot trader and the header. No outlet pipe and valve shall be installed between safety valve and drum or header.

(3) the pilot safety valve should have the device to prevent the self moving of the heavy hammer and the lever that limit the lever deviant. The spring type safety valve should have the device to lift the hand and prevent the screw from being unscrewed.

(4) for a boiler with rated steam pressure less than or equal to 3.82MPa, the throat diameter of the safety valve should not be less than 25mm: for the boiler with rated steam pressure greater than 3.82MPa, the throat diameter of the safety valve should not be less than 20mm.

(5) the connection area between the safety valve and the boiler should not be less than the inlet section area of the safety valve. If several safety valves are installed together in a short tube directly connected to the pot, the passage area of the short pipe should not step 1.25 times the area of all the safety valves.

(6) safety valves should be equipped with exhaust pipes. The steam draining pipe should go straight to the safe place and have enough section area to ensure that the exhaust steam is unblocked. The bottom of the safety valve exhaust pipe should be put on airs, there is a drain pipe that receives the safe place, and no valve is allowed on the exhaust pipe and drain pipe.