Installation Of Differential Pressure Transmitter For Flow Measurement In Liquid Service


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There is a water injection line and flow is measured using differential pressure transmitter. The flow element is orifice plate. Flange taps for flow measurement is at an elevation of 500 mm from the deck level stancion mounted transmitter needs to be installed at an elevation of 1.5 Mt at the same deck level since there is no deck below for mounting of transmitter being a liquid service.

Also the piping isolation valve is a double block and bleed arrangements and is very close to the grating of the deck. The tapping orientation is at 45 deg angle based on liquid service. The impulse lines have mandatory got to be piping and not tubes. Hence flexibility in routing is reduced.

Can anybody advise on the transmitter installation for accurate measurement in spite of elevation discrepancy.
The best advice I can give is do whatever it takes to keep your DP element below the flange tap level... but that somewhat depends on design DP. If design LRV is well above the 1m W.C. DP, no problem. If flow accuracy is required anywhere close to 1m W.C. DP, element placement below taps is a must IMO. Use a remote-element transmitter if need be.
I've never had to use a bubble pot but it appears to be a condensate pot with a valve for releasing/purging collected air/gas/vapor at an elevated high point. I'm not quite sure why any collected gas will not create head pressure errors at the DP transmitter, like when an automobile's hydraulic brakes get 'mushy' with air in the system.

There's a good illustration of a liquid installation of a DP cone meter using bubble pots on page 18, here: