Safety valves: pressure calibration stages and methodology
Safety valves are critical components in any pressurized system — boilers, compressors, tanks, or industrial installations. Their purpose? To release excess pressure and prevent any risk of explosion or material damage.
But to fulfill this role effectively, they must be accurately calibrated, meaning adjusted to open at the exact pressure defined by the manufacturer or relevant standards (API, ASME, etc.).
Purpose of Pressure Calibration:
- Identify the valve (reference, pressure range, type of fluid, use).
- Note the set pressure.
- Isolate the valve from the system if fitted.
- Ensure that the test devices are calibrated themselves (ISO 17025 traceability).
Pressure Calibration Methodology
1. Valve Preparation
- Identify the valve (reference, pressure range, fluid type, usage).
- Record the set pressure (Set Pressure).
- Isolate the valve from the system if it is already installed.
- Ensure that all testing devices are themselves calibrated (ISO 17025 traceability).
2. As Found Test (Before Adjustment)
- Mount the valve on a pressure test bench (hydraulic or pneumatic).
- Apply pressure gradually.
- Read the actual opening pressure (Pop pressure).
- Note any deviations from the set point.
This test indicates whether the valve has drifted and whether readjustment is necessary.
3. Mechanical Adjustment (Tuning)
- If the valve does not open at the correct pressure:
- Remove the cover
- Adjust the spring tension or adjust the disc according to the design.
- Carry out several tests until the target opening pressure is reached..
4. Pop Test
- Perform a dynamic aperture test, observing :
- The "pop" noise (sudden release).
- Exact release pressure.
- The responsiveness of the mechanism.
- Make sure the valve closes properly after release.
5. Leak Test (Bubble Test)
Use a visual method (foam solution or immersion) to:
- Check valve tightness below the set pressure.
- Detect any premature leakage.
6. As Left Test (Post-Calibration)
- Record the final opening pressure after adjustment.
- Ensure compliance within acceptable tolerance (typically ±3% of the set point).
- Issue a calibration certificate including:
- Before/after results.
- Test conditions.
- Equipment used.
- Traceability references.
Equipment Used
- Pressure test bench (air or water).
- Precision manometer or digital sensor (calibrated).
- Manual or automatic pumps.
- Cameras or sensors for bubble testing (tightness).
- Calibration management software.