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3Z Double Block and Bleed (DBB) Valve
This system is designed to relieve excess pressure rise in the body cavity of a closed valve due to
ambient temperature causing expansion of the liquid in the valve. The relief valve is set to open
at 25 PSI on all valves, regardless of their working pressure. With the Double Seal valve closed,
the relief valve will open at 25 PSI above upstream pressure. This system functions only
when the Double Seal valve is closed and the isolation valve is open.
Specificity
● ZERO LEAKAGE
A valve selection is very important in petroleum industry. An wrong valve selection causes the decrease of income, the pollution of product and the increase of product line maintenance cost.
In multi-product system, valve should stand cycle variation of frequent and cut off completely in up-stream sealing and down sealing. Double block and bleeding valve is developed for satisfying a demand fact of metering station, tank farm marine loading docks, blending plant.
● NO ABRASION
D.B.B can do complete isolation without leakage in a design pressure ,and the design of valve is that a seal doesn t contact with valve body during valve opening or closing. The moment the last of closing operation a seal contacts with body, the force consists of only pressure force. A shearing force doesn t be suspended. In all opening, handle operation, a seal in separated form body, and maintain this state during plug rotation. This takes off the abrasion of seal and extends a life.
● Double block & bleed
In D.D.B, there are up-stream seal, down-stream seal, and bleed point for each other. So as a one valve, it can substitute for two valve and one spool piece, drain. The spool drain sends leakage fluid of valve to tank.
The bleed system in this valve is installed for proving a zero leakage.
