CONTROL VALVE LEAKAGE CLASSIFICATION
Class I
Maximum Seat Leakage:
As agreed between customer and supplier
Test Media:
None Required
Class II
Maximum Seat Leakage:
0.5% of rated capacity
Test Media:
Clean air/water @ ambient temperature, 45-60 psi-g
Class III
Maximum Seat Leakage:
0.1% of rated capacity
Test Media:
Clean air/water @ ambient temperature, 45-60 psi-g
Class IV
Maximum Seat Leakage:
0.01% of rated capacity
Test Media:
Clean air/water @ ambient temperature, 45-60 psi-g
Class V
Maximum Seat Leakage:
0.0005ml per minute, per inch of seat diameter, per PSI differential
Test Media:
Clean water at ambient temperature, maximum service pressure, above 100 psi-g
Class VI
Maximum Seat Leakage:
Variable, eg. 3 bubbles/min for 2" valve, 6 bubbles/min for 3" valve. Refer to ANSI/CI 70-2 for complete values.
Test Media:
Air/nitrogen at ambient temperature, 50 psi-g
Bubble-Tight
Isolation valves are generally marketed as bubble tight. It is widely accepted that "bubble-tight" refers to a valve that, when fully closed, does not pass any bubbles when one side of the valve seat is pressurized with air/nitrogen, and the other side of the seat is submerged in water. Actual test procedures can vary from manufacturer to manufacturer. There is no formal standard to define bubble-tight.
