A Double Isolation & Bleed (Double Piston Effect seat) valve is a valve with two seating surfaces each of which provide sealing in both directions in the closed position, with a means of a cavity vent or relief valve between the seating surfaces: seats are designed to seal with pressure from body cavity. Pressure test is performed without the relief valve which should be removed if fitted, the valve and its cavity are completely filled with test fluid:
DIB-1 (both seats bi-directional) the test pressure shall apply successfully to each valve, each seat should be tested separately from the upstream side;
DIB-2 (one seat uni-directional, one seat bi-directional) the test pressure shall apply successfully to each valve end, each seat should be tested separately from the upstream side first, and then test the bi-directional seat with simultaneous pressure to the valve cavity and the upstream end.
Fluid detection shall be monitored by overflow through the cavity pressure relief connection.
