Safety Valve Spring Relaxation: Why Set Pressure Drifts Over Time
A safety valve’s spring looks like a simple component, but it is the heart of set pressure control. Over time, springs relax. The valve opens at a lower pressure than intended. This drift is silent, invisible, and dangerous.The main safety valve product names of China Safety Valve Network include:Hydraulic Safety Valve,Impulse Safety Valve,Impulse Spring Safety Valve,JIS Safety Valve,Main Safety Valve,Overflow ValveOil Refining Specific Safety Valve,Pulse Safety Valve,Pilot Safety Valve,Pressure Safety Valve,Quick Switching Safety Valve,
Why springs relax
Every spring under constant compression slowly loses force. This is called stress relaxation. High temperature accelerates it. A carbon steel spring at 300°C may lose 10–15% of its set load within two years. Vibration from nearby rotating equipment also speeds up relaxation.
The result: premature opening
If the spring loses preload, the safety valve opens below the set point. A valve designed to open at 10 bar may pop at 9 bar. The process runs below design pressure, but nuisance releases waste product, damage seat surfaces, and cause unscheduled downtime. In steam systems, frequent small releases also erode internal parts.
How to detect spring relaxation
Most plant inspections check only the set pressure at the test bench. But that test compresses the spring again – it does not reveal long‑term relaxation. Better methods:
Keep a log of each valve’s set pressure over successive calibrations. A downward trend indicates spring relaxation.
For critical services, use a pilot‑operated safety valve. The main spring sees no process fluid or heat, so drift is minimal.
Replace springs every 5–7 years in high‑temperature or high‑cycle services, even if set pressure still passes.
What to do about it
When a spring‑loaded safety valve shows set pressure drift, do not simply re‑adjust the spring screw. The spring has already lost its original characteristic. Replace the spring or the entire valve. Order springs with low‑relaxation alloys (e.g., Inconel X‑750 for high temperature).
One practical rule
If a safety valve needs adjustment more than twice in three consecutive calibrations, replace the spring. Do not chase the set point – fix the root cause.
Bottom line: spring relaxation is real. Monitor set pressure trends, replace springs proactively, and consider pilot‑operated valves for hot or critical services. Your safety valve should open when it must – not earlier, not later.
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