Transmitter is connected such as L side to water level (positive head) and H side to vacuum with condensate pot. During calibration I observed that air suck from L side impulse line which is connected to water level head. How it is possible? Please explain if know anyone.

Vacuum under tank is -674 MMWCL
Water level in tank is 850 MMWCL
URV is 0 MMWCL

 

How in the world do you observe 'air' being sucked from the Low side impulse line? How is it possible that you observe it?

Why would there be 'air' in the low side impulse line in the first place?

Do you make an effort to make sure there is liquid fill fluid in the lower impulse line? What plumbing do you have to ensure that?

Is the 'air' really vapor from the liquid that is flashing because its temperature is higher than the boiling point of the liquid at the vacuum level you're working at?

Is the DP at the same datum elevation as the bottom port, below or above?

Do you expect to maintain a liquid head below the condensate pot on the upper impulse line (the one connected to the DP low side) Does the liquid level maintain itself? What is the fill fluid?

URV = 0 mm wc. What is the LRV?

Has this arrangement ever worked properly, providing a decent level measurement?

 

The atmosphere outside the vessel is pressing in at a pressure of 1 bar.

If the liquid head pressure and the vacuum combine to be less than 1 bar pressure inside the vessel at the lower port, then air could leak into the vessel.

Is the liquid level times its specific gravity plus the vacuum level less than atmospheric pressure?

1 bar = 10197mm wc

 

The only way you could see air is if you are using plastic lines.
I am guessing your fittings are leaking. Do you have support inserts in the plastic lines? I have seen several applications in China where the stainless fittings leak like a sieve. I watched one instrument mechanic take out all the stainless ferrules and replace them with layer on layer of Teflon tape.

 

H side of DP cell should be sensing the bottom of the tank. L side should be sensing the top of tank and the L sensing line should be completely filled with the fluid. Any leaks in either sensing line will pull vacuum. Your transmitter range should be set for Zero (maximum negative pressure) and span (atmospheric pressure)

> Transmitter is connected such as L side to water level (positive head) and H side
> to vacuum with condensate pot. During calibration I observed that air suck from L side
> impulse line which is connected to water level head. How it is possible? Please explain if know anyone.

> Vacuum under tank is -674 MMWCL
> Water level in tank is 850 MMWCL
> URV is 0 MMWCL