This needs a diagram or P&ID to be sure, but would seem to be valid.

So long as the pump can supply both trains, the PCV letting down pressure is ok so long as you have suitable precautions to prevent over pressure of the LP system.

This needs to be looked at in a HAZOP or MOC procedure.

Your issue is flow capacity as a diaphragm pump is a PD unit so only supplies a given amount. How are you increasing flow?

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The higher pressure of the chemical injection system is to ensure there is no backflow contamination issue. And, the flow control valve may be added on each injection point for adjusting the chemical quantity as required.

I'm not sure a pressure control valve on a PCV pump is going to work if you are controlling upstream pressure. The pulsation frequency is likely much faster than the loop response time, so you will end up with a system that cannot response quickly enough to the constant pressure cycles.

Air powered diaphragm pumps are not purely "PD" pumps that output the same flow at whatever pressure. As you increase pressure and/or fluid viscosity, the pump will physically slow down the pumping cycles, lowering flow rate.

P& I D or some process sketch pls; otherwise a vague post.

Hi,
PVC ,PIT ?? Are you familiar with the terminology used for PID and instrument?
Please explain what you are talking about and supply a sketch/PID for us to understand your post.
Note: Not a good idea to install valve(s) at the discharge of PD pump (safety and environment concern).
Cheers,
Pierre

Who is the manufacturer of your pumps ?...... Why are you witholding obviously important information ?

MJCronin
Sr. Process Engineer

I'm assuming PVC means PCV.

And that the LP connection is essentially a tap from an open ended HP feed.

But no diagram or response from the IP we're all at sea...

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.