PRVs in Water Booster Stations

[Jeamon]

I am finalising a design on an inline water booster station that will be supplying a low pressure zone in a Town's distribution system. The pressure zone we will be pumping into is a closed system (i.e. no elevated storage tank/pressure tanks). The pumping station will be equipped with centrifugal pumps on VFDs. In previous designs we have always included a pressure relief valve and we have always piped the PRV to atmosphere by piping it through the wall with a downturned elbow. Our client has asked us why we aren't discharging our PRV to the suction header as he pointed out that other booster stations in his system do that. Upon researching this, I have noticed that a lot of packaged booster pump station suppliers do this. Is this good design practice?

Some points I have against doing this are:

- If there is high pressure/pressure surge upstream of the booster station, our PRV will be able to vent the pressure
- If there is high pressure in the discharge header, you will be relieving pressure into a closed system.

Any comments would be appreciated.

Thanks

Josh

 

[yogibear1]

Actually what is needed is a PLC (programmable logic controller) which can handle the various logic scenarios for the system, not just the booster pumps, and take the appropriate action. VFD pumps and PLC's are a happy marriage and work well together.

Since centrigual pumps heat up when the flow is low or on the far left side of their curve, a return line would optimally run back to a storage tank or other large reservoir. Recirculation back to the suction side is quite normal, but one has to be realistic about the potential for overheating and what that does to the pump.

A possible solution for low flow is for the pump to shut down and a bypass line open up letting the upstream pumps take the load. Also, one may consider use of a jockey pump, smaller than the booster, maybe 1/3 the size or even less with quite low flow and just maintaining the pressure.

 

[Amzad]

Hi Josh, in most large distribution systems I am familar with we do relief pressure into the suction header to protect enviroment(fish habitate) and so far have not had any problems with increase in system pressure. I assume your relief line is of smaller diameter than the suction header so the pressure dissipation into the suction will normalize. I should mention we encountered some air entrainment in the pumps during pressure relief and installed baffles in soem cases move teh reflief line furtehr away from teh pump inlet.

 

[abcmex]

Josh,
have you think about why the package units have the PRV connected like this? understanding the original assumptions will help you ;-). I would be concerned to transfer the pressure surge from a higher pressurized system to a lower pressure system.

rgs