Booster Pump Station Design- Public Water System

[cuels]

I am designing my first Booster Pump Station. The pump station will be pumping from a storage tank to a higher pressure zone system. There will be three pumps, (1) 1900 gpm (150 hp) pump and (2) Duty pumps 45 gpm (2hp). They will be connected by a manifold on the suction and discharge side. The 1900 gpm pump will be used for fire hydrant supply only (1500 gpm fire flow demand) and the smaller pumps will be used for the daily demands.

I am trying to learn about the "desirable" piping, valve, and tank configurations to minimize the effects of transient "surge" pressures. All of the pumps are on Variable Frequency Drive units. At first I was just going to use these and swing check valves to ease in and out of pump cycles. However, there isn't a lot of information about the "tried and true" configurations used for booster pump stations.

My question is: does anyone have any in-service stations that work well, and what are those configurations? Also, will I get myself into trouble by relying solely on the VFD's and swing check valves to minimize surge effects and do I need to seriously consider a surge tank? Does anyone have any design tips for sizing a surge tank?

 

[bimr]

The only difficult aspect of this pump station design is the selection of the pump sizes.

Use of VFD's and the swing check (or silent checks) will eliminate the potential of transient "surge" pressures. It is recommended that you also avoid high pipe velocities (greater than 5 ft/sec as well). You do not need a surge tank. Use eccentric reducers on the pump suction side to avoid entrapment of air.

The typical arrangement for pump station piping is a suction manifold at grade and a discharge manifold elevated. That would allow the operator to walk directly up to the pump from the discharge side without stepping over piping. The building is slab on grade, single floor.

The pump station that I was involved with was similar. The system pumped from a ground storage tank directly into a small town water distribution system. No elevated tank. The peak day flow was around 600 gpm, average daily flow was 60 gpm, and the high fire flow. The peak hour/average daily flow ratio can be estimated as 10 times with such a small pump station. I also put in a surge valve to release pressure from the discharge side of the pumps back to the ground storage tank. I was concerned with the flow dropping to zero in the middle of the night.

The rated capacity of a pump station is typically the capacity of the pumps with the largest pump out of service. So your example, your pump station would have a rated capacity of only 45 gpm.

You should carefully consider installing a spare pump of the largest pump in the pump station. Therefore, you should have (2) 1500 gpm pumps and (2) 45 gpm pumps. The smaller pumps are relatively inexpensive.

 

[semo]

Bimr has a lot of good points. A couple more that I will mention include the use of the silent check instead of a swing check. The swing has enough movement (slower close) that it will impart some hammer when it closes. The silent check closes much quicker because of a shorter closing length.

The VFD's should attenuate the sudden surges from the pumps; but, a couple other methods I've seen are to:

1. Install a pressure relief valve between the discharge header and the suction header. You can set the pressure a little higher than the discharge pressure of the pump.

2. Use a pump control valve that will be closed when the pump starts and slowly open and then slowly close before the pump is turned off.

These methods are typically used with regular (across the line, reduced voltage, etc.) starters; but, method 1 can be used as a backup to the VFD to take care of power outages or if your VFD has an across the line backup.

 

[cuels]

Thanks for the tips. Do either of you have any good sources for the design of piping and valve configurations... or for the design of booster, lift, etc. stations?