The valves manifolds are devices that are associated with the DP transmitter, The device isolates the DP transmitter from the process, for maintenance and calibration process.
There are 3 valve manifold and 5 valve manifold.
3 Valve manifold:
The three valve manifold is shown inside the dotted box consisting of an equalizing valve and two block valves. There is an extra bleed valve used to vent trapped fluid pressure to atmosphere.
Three-valve manifolds are more commonly manufactured as monolithic devices: the three valves cast together into one block of metal, attaching to the pressure transmitter by way of a flanged face with O-ring seals.
In normal working mode, the blocking valves are opened and the equalizing valve is closed tightly so no fluid flows from high to low-pressure side. For calibration or maintenance, the block valves are closed and the equalizing valve is opened. The procedure to close the valves is first to close the high-pressure valve then open equalizing valve then close the low-pressure valve.
5 Valve manifold:
The presence of a built-in bleed valve in the five-valve manifold allows the technician to vent trapped pressure through a tube to some remote location, rather than directly venting at the transmitter.
The equalizing valve is never allowed to open while both the block valves are open. Doing so will allow process fluid to flow through the equalizing valve(s) from the high-pressure side of the process to the low-pressure side of the process.
During normal operation both the equalizing valve and the bleed valves are closed and both the block valves are allowed to open.
And during calibration, both the equalizing valves and bleed valves are opened. and the block valves are shut off.
Pressure transmitter valve manifolds also come in single block-and-bleed configurations, for gauge pressure applications. Here, the “low” pressure port of the transmitter is vented to atmosphere, with only the “high” pressure port connected to the impulse line