Breizh is right, if there was gas passing through, it would impact the flowmeter reading as well. But this fluctuation would be quite substantial and it would be quite observable by the pump discharge pressure instrument. In the first post, it was mentioned the pump discharge pressure is steady, but it is now mentioned that the pump discharge does indeed fluctuate but not remarkably. The drawing does seem to imply this is the lean amine flow, might not be that much of CO2 gas remaining, and it would be odd to have such a substantial quantity of gas to affect the magflow anyway.....
Perhaps a short video of the observed fluctuation or maybe some trends will help.
Also, does the valve have a manual override handwheel? I presume when you mentioned manual, you are referring to the PID controller manual right? If a handwheel exists, might you try to move the handwheel to the current valve position and force the valve to remain steady at the current position rather than by using the PID controller manual. If the flow becomes steady after you have forced the valve to the fixed position, (and that the valve is not moving at all) then the problem is due to the valve. Try this on both sets of valves, the FV-A/B and the valve linked to FT145, or maybe try on both at the same time, see if it stops the fluctuation.
These new valves that you mentioned, these are new globe valves? Same type as the previous valves or a new type? Possible valve trim issue?
When you mentioned modification job done previously? What was the modification? Many a time when people tell me they modified something and then a problem appears and they ask me what to do next, I just tell them to undo whatever modification they made. Maybe the modification is somehow linked to this problem.
If the valve is not the issue, probably the next thing is to check the pump. Might you be able to measure the pump current? Clamp on perhaps?
Edited by thorium90, 27 May 2018 - 04:37 AM.