While there are some common problems that may be encountered with safety valves and their solutions, it is also critical that safety valves are properly selected, installed and maintained. Below are some key messages and recommendations:
Common Safety Valve Problems and Their Solutions
Valve flap does not return to seat after discharge
Cause: Bent spring, incorrect stem or flap installation position, stuck.
Solution: Reassemble the safety valve.
Leakage
Reason: Dirt on the sealing surface, damage to the sealing surface, bending of the valve stem or skewing of the lever and pivot point.
Solution: Use a lifting wrench to open the valve several times to flush out dirt; grind or turn and then grind to repair the sealing surface according to the degree of damage; reassemble or replace damaged parts; replace the spring with reduced elasticity.
To the specified pressure does not open
Reason: the fixed pressure is not allowed, the valve flap and the valve seat stick, the lever is stuck or the weight moves.
Solution: Re-adjust the spring compression or the position of the weight; carry out manual venting or draining test regularly; re-adjust the lever and the position of the weight.
Pressure continues to rise after venting
Reason: the safety valve displacement is smaller than the equipment safety discharge volume, the valve stem center line is not correct or the spring rust, exhaust pipe cross-section is not enough.
Solution: Choose the appropriate safety valve; reassemble the valve stem or replace the spring; replace the exhaust pipe that meets the safe discharge area.
Frequent jumping or vibration of valve flap
Reason: spring stiffness is too large, improper adjustment of the adjusting ring, excessive resistance of the discharge pipe.
Solution: Change the spring with appropriate stiffness; readjust the position of the adjusting circle; reduce the resistance of the discharge pipe.
Less than the prescribed pressure to open
Reason: pressure setting is not allowed, spring aging.
Solution: Properly tighten the adjusting screw or replace the spring.
Principles of safety valve selection
Steam boiler: generally use open full opening spring safety valve (such as 0490 series).
Liquid media: generally use the micro-opening spring safety valve (such as 0485 series).
Air or other gaseous media: generally use closed full-opening spring-loaded safety valve.
Liquefied petroleum gas car tanker or railroad tanker: generally use the full-opening internal safety valve.
Outlet of oil extraction wells: generally use pilot-operated safety valves.
Steam power generation equipment, high-pressure bypass: generally used with safety and control of the dual function of the pilot-operated safety valve.
Regular opening tests are required: safety valves with lifting wrenches should be used.
Higher medium temperature: Safety valves with heat sinks (over 300°C closed and 350°C open) should be used.
Change of outlet back pressure: bellows safety valve should be used (change more than 10% of the opening pressure).
The medium is corrosive: bellows safety valve should be selected to prevent parts corrosion.
Safety valve installation and maintenance precautions
Installation location, height, import and export direction must meet the design requirements, the direction of media flow and the valve body arrow consistent, firmly and tightly connected.
Appearance inspection before installation, to ensure that the valve nameplate in line with national standards, the working pressure is greater than 1.0 MPa valve needs to be strength and tightness test.
The safety valve should be installed vertically with no resistance at the outlet to avoid pressure.
The sealing should be tested and checked before installation.
Safety valves in use should be inspected periodically.
Following these recommendations will ensure proper operation of safety valves and improve the safety and reliability of industrial equipment.
