Pilot type safety valve is a safety valve, its opening and closing parts under the action of external force in a normally closed state, when the device or the medium pressure inside the pipe increases, exceeds the set value automatically open, through the medium outside the system to prevent discharge piping or equipment in the medium pressure exceeds the set value. The pilot safety valve is widely used in natural gas, petroleum gas and chemical pressure vessel and industrial pipeline. It has many outstanding advantages, such as fireproofing, explosion-proof, antistatic, reliable sealing, quick opening and closing and large discharge volume.

Structural characteristics of pilot safety valve

A pilot safety valve consists of a main valve, a guide valve, a relief valve, a joint and a catheter, etc. Under normal conditions, the medium pressure of the system acts both below the main valve and the upper valve of the main valve.

The main valve is closed under the action of pressure difference due to the area of medium acting on the air chamber above the main valve. With the increase of pressure in the pipeline medium, the sealing pressure will also increase with the seal, which is just the opposite of the direct load safety valve, that is, the higher the medium pressure is, the more reliable the seal is. When the medium pressure pipeline is abnormal, reaches or exceeds the set pressure, the pilot valve (Figure 2) on the valve to open quickly, and the top of the valve chamber medium quickly discharged through the exhaust joint pilot valve, main valve force under medium pressure, instantaneous opening, will quickly from the medium the main valve exports a lot of discharge, the pressure of the medium in a pipeline to restore to the normal working pressure, ensure the safety of the system.

When the pressure of pipeline medium is reduced to about 90% of the setting pressure of the safety valve, the valve flap on the pilot valve is closed, and the pipe way enters the gas chamber above the main valve flap through the pilot valve. Under the effect of pressure difference, the main valve is closed, which ensures the normal work of the system.

Working principle of pilot safety valve

The guide valve consists of the valve body, the lower valve disc, the top rod, the air vent joint, the upper valve, the spring and the discharge valve.

Under normal operating conditions, the valve on the guide valve is in the closed state, and the valve flap under the guide valve is in the open state. The pipe medium goes through the lower valve into the air chamber above the main valve and closes the main valve. When the medium pressure pipeline is abnormal, the whole force reaches or exceeds the set when the pilot valve under the valve valve under pressure in the medium, cut off the pipeline medium into the main valve at the top of the channel, while the pilot valve on the valve by the push rod, the pilot valve opens, and the top of the valve chamber of the medium quickly discharged through the exhaust joint. Under the strong action of the medium pressure, the main valve disc is opened instantaneously, and the pipeline medium is discharged rapidly from the outlet of the main valve, so that the pressure of pipeline medium is restored to normal working pressure and the safety of the system is ensured. When the pipeline pressure drop to the system settings of the set pressure of about 90%, the pilot valve on the valve under the action of the spring off, while the pilot valve under the valve was the top open, medium pipe into the gas chamber main valve above the valve through the valve, the main valve under pressure to close, to ensure the normal operation of the system.

When the pressure of pipeline medium is abnormal and the pilot valve fails to open, it can manually open the relief valve on the pilot valve, release the medium in the upper chamber of the main valve, open the main valve, release the abnormal pressure of medium in the pipeline, and ensure the safety of the system.

Installation requirements for pilot safety valves

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

(2) the pilot safety valve should be installed vertically in the highest position of the pot merchant and the collection box. Between the safety valve and the pot or the set box, the outlet pipes and valves for the use of steam shall not be fitted.

(3) the pilot safety valve must have the device to prevent the self moving heavy hammer and the guide bar which limits the lever deviate. The spring safety valve should have the device to raise the handle and prevent the screw to be adjusted at any time.

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

(5) the connecting pipe of the pilot safety valve and the boiler shall be not less than the section area of the inlet of the safety valve. If several safety valves are mounted on a short pipe directly connected to the drum, the section area of the short pipe shall not exceed 1.25 times of the exhaust area of all safety valves.

(6) the pilot type safety valve should normally be installed in exhaust pipe, exhaust pipe should be through a safe place, and with sufficient cross-sectional area to ensure that the exhaust flow. The bottom of the exhaust pipe of the safety valve should be loaded with a drain pipe that receives the safe place, and the valve is not allowed on the exhaust pipe and the drain pipe.