DP Type Flow Transmitter on Vacuum Column


Thread Starter


We have DP Type flow transmitter on pump discharge and this goes to a column under vacuum. DP transmitter is installed 1.5 meters below the orifice.

Production says flow is not correct and when we try to check by opening the LP or the HP vent, we can feel the vacuum form there. Is the installation correct? or anything else can be done?

D/P transmitters work in such installations, but you need to elaborate.

For example,

1. Type of meter, upstream and downstream run length,

2. Where is the square root extraction being done (in transmitter or in monitor/DCS).

3. Pipe size, flow rate, nominal fluid properties and phase, etc.

4. How much error are you seeing, and the flow relative to the indicator scale maximum.
We need to know more information such as:

1. Does the transmitter zero properly?

2. If the flowmeter has worked properly before, has anything changed?

3. Is this a new installation? Has it ever worked?

4. Has the flow meter calibration been checked?

5. By how much does production think it is reading wrong?

6. What is the basis for production thinking the meter is reading wrong? Material balance for example.

7. What have you done to troubleshoot the problem except verify the port are open?

William (Bill) L. Mostia, Jr. PE
ISA Fellow
WLM Engineering Co.
The fact that it's under vacuum shouldn't worry a DP cell unless perhaps it's flashing off across the orifice, any noise or vibration?

Is your transmitter reading higher or lower than production estimate?
I once struck a installation where square root was done in the transmit then again in the DCS, it made the reading higher than actual.

Can you measure the gauge pressure at one of the taps?

Where is the DP element in relation to the vessel entry, above or below, how far? Post a sketch if you can,

What is the process fluid / temperature?