I have used a dp tranmiter for measuring and controls the flow of the liquid ammonia. But i dont have a acceptable control because the dp reading very changabele. I replaced the transmiter with another new but bug so there is.Please advise me how i can have a good control with bottom description.
very thanks
Farhad Rabiee Roudsari

MAIN LINE : 3"
LIQUID : AMMONIA
BRANCH : 1/2" SS lenght 0.5 meter face to face of main line without tracing
DP TRANS. : 1151DP ROUSEMOUNT
RANGE :0-50 Mbar

 

I'm not sure what problems you are having. When using a DP type transmitter, the high pressure tap should be on the bottom of the vessel, the low side tap should be above a level that the liquid will never reach to compensate for the actual vessel pressure. From that, you can measure the physical distance between taps, multiply by the specific gravity, and that is your range. For example, if you are measuring a vessel with high and low taps at a physical distance of 120" apart, and you assume the specific gravity of liquid ammonia is .6819, your 0-100% range would be 0-81.828"H2O or 0-203.82 millibars. One installation issue that can cause problems is accumalation of liquid in the low side tap.

 

Are you using an orifice plate? Could you be flashing the ammonia into gas across the orifice?

 

Well that was no answer at all. He has a flow problem, not level.

This sounds like a classic two-phase problem caused by the ammonia flashing across the orifice. You are sometimes getting the liquid flow dP, and then a much higher dp because the flashing converts the liquid ammonia to a gas. We can't tell because you didn't give us the downstream pressure. If the downstream pressure is such that ammonia is a gas, then you will get flashing at the orifice -- an orifice cannot be used for such a measurement. You may need to redesign the system to maintain a higher pressure downstream of the orifice.

Dick Caro
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I agree with Dick. Check your vapour pressure. I agree that you are more than likely "flashing" across your primary element. An increase in your back-pressure would solve your issue... it is not likely to be your xmtr.

Cheers,
Roley