Pilot-operated safety valve is a kind of safety protection valve. Its opening and closing parts are normally closed under the external force. When the medium pressure in the equipment or pipeline rises and exceeds the specified value, it will be automatically turned on. By discharging the medium to the outside of the system To prevent the pipeline or equipment media pressure exceeds the specified value. Pilot-based safety valve is widely used in natural gas, LPG and chemical pressure vessel equipment and industrial pipelines, with the outstanding advantages of fire proof, anti-static, reliable sealing, quick opening and closing and large displacement.
Analysis of Working Principle and Structural Features of Pilot Safety Valve
Pilot-type safety valve structure features pilot-operated safety valve by the main valve, pilot valve, relief valve, connectors and pipes and other components. Under normal conditions, the medium pressure of the system acts not only below the main valve flap but also above the main valve flap. As the role of the main valve above the air chamber medium role in the area below the medium area, under the pressure difference, the main valve flap is closed. As the pressure in the pipeline increases, the seal will also get a higher specific pressure with increasing pressure, which is exactly the opposite of a spring loaded direct relief valve, which means that the higher the pressure of the medium, the more reliable the seal. When the pipeline medium pressure anomaly, reaches or exceeds the set pressure, the pilot valve (Figure 2) on the valve quickly opened, the main valve above the air chamber through the pilot valve exhaust connector quickly expelled the main valve flap in the bottom medium The strong pressure, the instantaneous open, the media quickly exit from the main valve a large number of outlets, so that the pipeline medium pressure back to normal working pressure, to ensure the safety of the system.
When the pressure of the pipeline medium drops to about 90% of the set pressure of the safety valve in the system, the valve disc on the pilot valve is closed and the valve medium also enters the gas chamber above the main valve flap through the pilot valve. In the role of pressure difference, the main valve is closed, to ensure the normal operation of the system.
Pilot-operated safety valve pilot valve by the valve body, the next valve, ram, deflation, valve, spring and relief valve and other components. Under normal conditions, the pilot valve on the valve is closed, the valve under the valve is open. The pipeline medium enters the gas chamber above the main valve flap through the lower flap valve, closing the main valve flap. When the pipe media pressure anomaly, to meet or exceed the set of the set force, the pilot valve under the action of medium pressure valve under the closure, cut off the pipeline medium into the main valve flap above the channel at the same time on the pilot valve flap top From the pilot valve open, the main valve above the gas chamber within the exhaust through the exhaust quickly. Under the action of the medium pressure under the main valve flap, the main valve flap opens instantaneously, draining a large quantity of the pipeline medium from the outlet of the main valve rapidly to restore the medium pressure of the pipeline to the normal working pressure to ensure the safety of the system. When the pipeline pressure drops to about 90% of the set pressure set by the system, the upper valve flap of the pilot valve is closed under the action of the spring and the lower valve flap of the pilot valve is opened by the ejector rod. The medium of the pipeline enters the main valve through the lower valve flap The gas chamber above the valve, the main valve flap closed under the pressure difference, to ensure the normal operation of the system. When it is found that the pressure in the pipeline medium is abnormal and the pilot valve fails to open, the relief valve on the pilot valve can be manually opened to release the medium in the air chamber above the main valve flap to open the main valve flap and release the abnormal pressure of the medium in the pipeline , To ensure the safety of the system.
Pilot-operated safety valve installation requirements (l) Boilers with a rated evaporation of more than 0.5 t / h shall be equipped with at least two pilot-operated safety valves: a boiler with a rated evaporation less than or equal to 0.5 t / h and at least one safety valve. Separable economizer outlet, steam superheater outlet must be equipped with pilot-operated safety valve. (2) Pilot-type safety valve should be installed vertically in the pot, the highest position of the header. Between safety valve and drum or header, there shall be no steam outlet pipe and valve. (3) Pilot-operated safety valves are to be provided with means to prevent the hammer from moving on its own and guides to limit the derailment of the lever. Spring-loaded safety valves are required to have lifting handles and means to prevent the adjusting screws from being loosely screwed. (4) For boilers with rated steam pressure less than or equal to 3.82MPa, the pilot-operated safety valve shall not be less than 25mm in throat diameter: for boilers with a rated steam pressure greater than 3.82MPa, the throat diameter of safety valve shall not be less than 20mm. (5) Pilot-type safety valve and the boiler connection pipe, the cross-sectional area of not less than the safety valve inlet cross-sectional area. If several safety valves are installed together on a short tube connected directly to the drum, the cross-sectional area of the short tube should not be 1.25 times the discharge area of all safety valves. (6) The pilot-operated safety valve should be equipped with an exhaust pipe. The exhaust pipe should be directly passed to a safe place with enough cross-sectional area to ensure the exhaust gas flow. Safety valve exhaust pipe should be installed at the bottom of the positon has received a safe place of the hydrophobic pipe, the exhaust pipe and the hydrophobic pipe are not allowed to install the valve.
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