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Symptom One: Premature Opening (Lift Pressure Too Low).

When the valve pops before the set pressure, the spring is not providing enough closing force. The first check is the adjusting screw and lock nut. If the adjusting screw has loosened or the lock nut was never tightened, the spring compression relaxes and the set pressure drifts downward. Tighten the adjusting screw clockwise to compress the spring, then secure the lock nut.

If adjustment alone cannot restore the set pressure, the spring has likely lost elasticity through fatigue, corrosion, or overheating. A weakened spring cannot balance the inlet pressure at the designed set point. Replacement is the only reliable remedy. For high-temperature service, note that a valve set at ambient temperature may open at a lower pressure once hot; re-adjustment or a different spring selection is required.

Symptom Two: Delayed Opening (Lift Pressure Too High)

A valve that fails to open at set pressure indicates excessive spring compression or a spring that is too stiff. Loosen the adjusting screw counterclockwise in small increments to reduce spring force. If the valve still does not lift, the spring stiffness may be above the required range for the service; a spring with a lower rate is needed. Before adjusting, confirm that the disc is not stuck to the seat from corrosion or debris, which mimics a high set pressure but is a mechanical fault, not a spring fault.

Adjustment Procedure and Verification

Set pressure adjustment must be verified by pop testing. Per ASME PTC 25, tolerance is plus or minus 2 psi for set pressures up to 70 psi, and plus or minus 3 percent above 70 psi. Perform a minimum of three consecutive pops; all must fall within tolerance. After adjustment, seal the adjusting screw and lock nut with lead seals or security wire.

Once set pressure is correct, verify blowdown by adjusting the blowdown ring. Moving the ring upward increases blowdown (lowers reseating pressure); moving it downward decreases blowdown (raises reseating pressure). Typical gas-service blowdown is 7 to 10 percent of set pressure.

Summary

Premature opening is corrected by increasing spring compression or replacing a fatigued spring; delayed opening by reducing compression or selecting a lower-rate spring. Adjust in small increments, verify with three pop tests within ASME tolerance, and seal the adjustment. Confirm blowdown with the adjusting ring only after set pressure is stable. If spring corrosion or permanent deformation is visible, replacement is required rather than adjustment.

Do you still need to know or purchase the following safety valve products:

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