The primary function of a double block and bleed valve is for isolation and the secondary function is for intervention (diverting / sampling / injection etc).
Double block and bleed valves operate on the principle that isolation can be achieved from both the upstream and downstream process flow / pressures. This is achieved by two ball, gate, globe, needle, etc. valves placed back to back, with a third "isolatable" valve in the centre cavity. Once isolation has been achieved in one or more of the main process isolation valves, the cavity that is created between these isolations can be drained. This is useful for flow diverting, sampling or injection situations, and for maintenance / integrity check situations where seat leakage can be monitored through the third "bleed" valve.
|Common Materials of Construction||Material Specifications|
|Standard Carbon Steel||ASTM A105|
|Low temperature Carbon Steel||ASTM LF2|
|Stainless Steel||ASTM A182 F316|
ASTM A182 F316L
ASTM A182 F304
ASTM A182 F304L
ASTM A182 F321
ASTM A182 F347
ASTM A351 CF8M
ASTM A351 CF3M