Are PRV's an Absolute on Centrifical Pumps?

It depends upon the findings of the HazOp Study, which is plant-specific.

In one of the steam plants that I worked at, on the boiler feed pumps, there had to be flow, otherwise the pump impeller would expand causing it to come in contact with the housing destroying the pump quickly. A PRV would allow sufficient flow through the pump to keep the impeller cool. I once saw a pump that had no flow, it was not a pretty sight.

That's a bypass (or Q-min) valve, not a PRV.

I would say it depends on the application of the centrifugal pump.

I work with, design completions, install and repair multi-stage centrifugal pump for the oil industry, where we place the pump in the well at about 5000 to 10,000 ft deep.

One of the unique things about a centrifugal pump is it lifts fluid, and once the stage or stages have lifted that fluid to the height that the stage or stages is design to do, then it lifts no more, therefore it can only maintain a column of fluid. This applies to any centrifugual pump.

Once the column of fluid has been achieved, the running current will drop and if a suitable motor controller is used and correctly set to trip on underload, then the pump will stop, as the current to maintain the column is less than the current to keep producing. With that being said, that same applies if the flow control valve or well head isolation valve is closed. The pump will lift to the closed valve, then as it cannot move the fluid further it then maintains the column with reduced motor current, and if the underload is set correctly the motor will trip. This does away with the need for a prv.

This is in the case of electrical submersible (multi-stage centrifugal) pumps used in the oil industry.

In your case... I would suggest a pressure sensor linked to the motor controller, so rather than waste condensate and have to install the additional piping to drain the fluid away etc..

You might want to look at the "Housing burst pressure" of the pump. That is the max psi the housing of the pump at full speed (assuming 2 pole motor @ 60Hz = 3600rpm and no VSD).

you will get some losses in your system, not as much as you would using 5000ft of 3 1/2 inch ID pipe, but providing your pump housing can handle the "Dead Head" discharge pressure, you have a suitable motor controller to monitor the motor running current and trips on underload, then in theory you should not get over pressure in the pipework.

However, the use or requirement to install/use a PRV depends on the rating of the pipework, who designed it, the requirments of the insurance company and safety regulations & practices.

it's better to have and not use rather than need it and not have it... just remember to do a little bit of regular maintainence on it now and then!!

Long back when I designed chilled water systems I generally include balancing valves, non return check valves etc .These valves are controlled by BMS . ( Building Management System).