Liquid in high side of dp transmitter. 2

[BWILDER12]

Im working on a dp transmitter at a natural gas plant that measuring flow. We cant keep liquids from building up on high side of the dp transmitter. The operators have to manually drain daily. The transmitter is mounted two feet above taps almost straight up and down. It is a line coming from dust filter to a product heater. Anyone have any advice on what we can do to not have to manually drain daily?

 

[Latexman]

Use remote, filled diaphragms.

Good luck,
Latexman

 

[TD2K]

If the transmitter is located above the taps is the liquid coming from condensation? Do you have any heat tracing in the area that would keep the process gas from condensing.

 

[moltenmetal]

Liquid can build up even in a VERTICAL leg as a result of "vapour lock", assuming the gas is saturated at a temperautre above ambient temperature so that the impulse legs and transmitter act as a condenser. You need to make the legs, and the root valves on the pipe, larger in diameter and free draining so each line is free to drain all the way from the transmitter back into the pipe. The liquid and gas must be able to pass by one another in the cross-section of the impulse line and the valve to permit the liquid to freely drain back to the pipe below: if the cross-sections are too small, surface tension prevents the gas from passing by the liquid and the liquid becomes "vapour locked". Depending on the liquid, free draining is more or less guaranteed with 1/2" OD tubing impulse legs (assuming the valves are no smaller in inner diameter than the tubing), but is not guaranteed in either 1/4" or 3/8" OD tubing impulse legs.

This assumes also that the DP transmitter can handle the saturation temperature of condensate forming on its diaphragms, otherwise you need to trap some condensate in there to allow the trapped condensate to cool to protect the transmitter. That trapped liquid needs to be present when the transmitter is zeroed.

 

[pmover]

moltenmetal, a star for you!
thanks for the explanation as i've encountered the same problem before and i could not understand why condensate collected in dP xmtr tubing located above taps. however, since increasing the orifice plate size, the "condensate" has not formed. what was more strange was the condensate collected only on upstream side of dP xmtr leg and not the downstream side. when the plate was removed/replaced, about a gallon of distillate was drained from the piping. no distillate since.

-pmover