The recurring dispute at a safety valve bench is treating “set pressure passed” as the whole unit passing. Set pressure, reseat pressure and seat tightness answer three different questions: when does it open, when does it close again, and does it hold once closed. They also need three different measurement arrangements, and a bench missing one of them leaves that part to eyesight and hand-written notes.
What each result actually tells you
- Set pressure. The pressure at which the disc lifts. What matters is pressurisation stability, sampling rate and how lift is detected. Raise pressure too quickly and the valve pops late, so the recorded set pressure runs high – the relevant standard caps the rate of rise, which means the bench has to control it rather than rely on an operator cracking a valve by hand.
- Reseat pressure. The pressure at which the disc closes again, and a readout on spring, disc and guide condition. Too small a reseat differential indicates chatter; too large means the valve is not relieving enough after lift. Both are defects, and both directions should be recorded separately.
- Seat tightness. Leakage past the closed disc at a defined pressure, and it needs a stable medium, a proper fixture and a defined leak measurement. The allowable value depends on seat construction: soft and metal seats differ by an order of magnitude, and the ISO 5208 class table gives the figure directly. Tightness is also a held test – hold time is banded by size, and a reading taken before the hold expires does not stand.
Questions worth asking before buying the bench
Does it cover direct-loaded and pilot-operated valves? Is the pressure range split into bands? Can fixtures be changed without re-piping? Are lift, reseat and leak curves recorded automatically? Does it stop on an exception rather than waiting for an operator? These decide acceptance far more than pump capacity does.
A few items that get missed: whether the pilot valve needs its own test position; what it costs to switch between air and nitrogen; whether high or low temperature samples need a separate ambient-temperature check path; and whether raw curves can be exported. A bench that issues a PDF verdict without the underlying trace cannot be audited when a result is disputed.
A calibration certificate is the start of traceability, not the end of it. How acceptance criteria map to the applicable standard, and how fixtures and channels should be configured for safety valves, is covered item by item in the equipment selection guide and can be worked through as a checklist with a supplier.
Ouxun configures fixtures, pressure intensifiers, acquisition and reporting around the valve connection, pressure rating and calibration procedure in use. Final parameters are set by customer samples, the applicable standard and the acceptance terms both sides sign.
Related test equipment
Each test above maps to a bench. Pick by valve type and by the item you need to prove:
- Valve pressure test machine — shell at 1.5x and seat at 1.1x, with a report per valve
- Valve comprehensive test bench — pressure, tightness, flow, torque and life cycling on one clamping system
- Valve testing equipment range — browse all models by valve type and test item