Shut Down Valve

Is this an old system that's been installed for years, or is the system designer still available? Ask the designer!

As for speculation, perhaps the designer has 'calibrated' the shutdown valve to some degree and is using the DP transmitter has a flow indicator, or maybe its there to measure for Pressure Hammer effects when the valve is closed, perhaps its to measure the time the valve takes to close, lots of different speculative reasons.

Ask the designer or do some exploring and see how the analog input to the controller is used. This will tell you a lot.

BD, you're assuming that the output of the transmitter is somehow connected to the valve. My guess is that someone wanted to be really sure that the stop/shutdown valve was closed tight (reading full upstream pressure, max delta P) or fully open (minimum delta P), and not stuck somewhere in between. On the other hand it could have been used as a crude position/flow indicator. As you said OP needs to track down the where the output goes, and what if any influence it has on the valve position. I'll bet it goes to a panel meter with red and black lines indicating the "proper" position of the valve.

Do you have a bypass line which is connected with another valve.

For example, suppose if the valve you are speaking about is on a 12" line.

Do you have a bypass line to the main line with a valve which is 2" or 4".

Let me know on that plz....

Cheers..