How much can you safely restrict a water pump's flow?

Question

I have a "Rainbow Lifeguard Quiet One 6000" external pump that I would like to use on a new chiller for my tank. The pump is rated at a little over 1500 gallons per hour. I'm debating between a couple of chillers, one that has a max flow rate of 1300 gph and another that has a max of 960.

I know that you are only supposed to put any valves on the outflow side of the pump and lessening the flow to 1300 from 1500 doesn't seem like it would be that big of a problem, but I was curious it cutting it back to 960 would be hard on the pump in the long run.

(I'm leaning towards the bigger chiller as although it may be overkill for my tank, it would let me have a little more water circulation.)

Answer 1

I wouldn't restrict it more than about 10% or so personally.

I would ask you to think about this: The rated flow rate on a pump is under perfect operating conditions and is usually a mathmatical model that cannot really be acheived in the real world. Your pump probbaly is several gallons per hours behind that. If the tank is on a stand and the pump on the floor, the head pressure alone may slow it to 1300 or below. Additional tubing, especially hard angles will further reduce the flow.

I would suggest you get a flow meter ( you can probably borrow one from a plumber for a day) and test the actual flow rate in your set up. Remember that the chiller will further reduce the flow itself. Odds are good you are closer to the needed 1300 than you think.

You can also install a small diverter valve in the line. Basically splitting the output from the pump into two lines. One can carry about 1250 GPH and the other the rest which it just returns to the tank unchilled.

Hope that helps

MM

Answer 2

ditto to magic