In case of diaphragm seal pressure transmitter is there any necessity to use integral manifold? Actually i wanted to know in case of direct mounting pressure transmitter if the pressure element is diaphragm then which one can be more suitable between integral manifold and diaphragm seal? Can we use both together?
The integrity of the capillary or seal/sensor volume is critical. That volume must be:
- completely free of gas/air
- completely filled with fill fluid
The slightest leak in a manifold valve stem seal or flange gasket and that integrity is gone and with it go the pressure readings.
The seal installation is done in the shop by vacuum evacuation and back-filling with fill fluid. It's not magic but it is a learned skill.
Putting a manifold valve (particularly a 5 valve with the potential for bleeding or opening a valve port to atm) between the seal and the transmitter is asking for trouble.
I see cut-and-paste specs where a 3 or 5 valve manifold is spec'd along with diaphragm seal(s). When it is brought to the attention of someone knowledgeable, the spec is always changed to eliminate the manifold valve.
I have seen shutoff valves installed between the process and the seal, and that makes sense.
I do see specs for a shutoff valve installed on an iso-ring seal. Theoretically, one could swap a capillary/instrument on an installed iso-ring in-line, if you know what you're doing and are lucky enough (like replacing a master brake cylinder on a car without needing to bleed the brake lines) to not lose any fluid or capture air during the procedure.