BY PRESSURE CLASS
Vacuum Service Valves
Service envelope language used in Chinese and ASME/GB catalogues. Class is not a substitute for the nameplate and the standard.
Choosing Vacuum Service Valves
Vacuum service requires an absolute-pressure specification and a defined leakage criterion. The process may be limited by ingress rather than outward pressure loss. Seat, seals, connection and cleanliness should be assessed for the actual vacuum range and fluid.
What to include in the RFQ
- State the operating absolute pressure and the pressure difference to atmosphere.
- Request internal and external leak-test methods, units and acceptance limits.
- Identify seal materials, gas composition, cleaning requirements and cycling duty.
Selection scenario
For an evacuated process vessel, separate leakage through the closed seat from ingress through the stem or connections. Include the required test method in the purchase specification.
Common selection mismatch
A positive-pressure rating or a bubble-tight description does not automatically establish the required vacuum performance.