I'm hoping I'm asking this in the right place. I'm trying to determine how I can improve the water flow within a project I'm working on.

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The flow starts out at the large water pump on the bottom left, flows through a radiator and into a water to air intercooler. Cooling the water to air intercooler should warm the water which will then flow to a tee where a part of the water will flow through normally and a small portion of the water gets sucked in by a smaller pump, pushed through an ESC and electric RC motor and continues back to the original pump.

The large pump flows 500GPH the small pump flows 90 GPH

The Diameter of the large pump and hoses is 3/4" and the diameter for the smaller pump is 5/16"

The water should be at 80*F (Or ambient temps) exiting the radiator and probably 170* after the intercooler, ESC, and Motor. (This are estimates as I don't really know the temps post radiator)

I have a small radiator I could place between the small pump and esc to cool the water more if needed.

My gut feeling is that the Tee's with the reducers are a poor choice thus why I'm asking how I could improve this system.

  • $\begingroup$ More information is needed for an intelligent answer. What is the pressure and flow rate of both pumps? What is the approximate inside diameter of the tubes in both circuits? Any idea what your temperatures might be; even some guesses would be helpful? What is the intercooler being used for? What bad things happen if either system fails? Is there provisions (reservoir or other) for make-up fluid and or air removal? $\endgroup$
    – ericnutsch
    Jan 2, 2016 at 20:44
  • $\begingroup$ I've added more information! I don't have a reservoir but have been thinking of adding one. The bad things that would happen would be that the electric motor or ESC die due to high temperatures $\endgroup$
    – calcazar
    Jan 2, 2016 at 23:23
  • $\begingroup$ Unless there are pressure differences, I would reduce this to a single pump design and tee off of the discharge of the large pump to supply the ESC. Advantages could be reduced weight and power requirements $\endgroup$
    – morristtu
    Jan 8, 2016 at 18:45

1 Answer 1


I am assuming that your question is "how to increase the flow rate" and that your pump is a centrifugal pump.

For centrifugal pumps, the flow rate out of the pump is dependent on the pressure at the exit of the pump. If the pressure is high, the flow rate will be lower. If the pressure is low, the flow rate will be higher. That dependency is typically illustrated for each pump in a graph of flow vs pressure which is called the pump's "pump curve".

For fluid systems with a centrifugal pump, the flow rate will be reduced by each element (tubing, fittings, valves, etc.) in the system. Each element added to the system increases the pressure and reduces the flow.

My first step would be to find the pump curve for your pump and measure the pressure at the exit of the pump. This will tell you two things:

  • is the pump operating correctly?
  • is the pump operating against a relatively significant pressure?

If the pump is not achieving the flow rate indicated on the pump curve from the pressure you are measuring, it may need to be rebuilt or replaced. If the pump is generating its maximum flow rate already, it will need to be upgraded.

If the pump is working correctly but not at maximum flow, you next step depends on the complexity of the system. It may be easiest and cheapest to upgrade the pump to one which will generate a higher flow rate against the pressure you are seeing. Or, it may be easiest and cheapest to investigate the other elements in the system and replace the problematic ones.

If upgrading the pump is not an option, you will need to determine where the restrictions are in your system. The ideal way to do this is to place pressure gauges in between each element and look for the highest pressure difference. I would start with one between pump and radiator, between radiator and intercooler, and between intercooler and pump. Whichever element has the highest pressure drop will be the one which is causing the most restriction to the flow.

Other thoughts:

  • I expect the interior loop is not reducing the flow rate substantially.
  • If the tubing is a significant restriction, increasing the inner diameter of the tubing can increase the flow rate dramatically. Reducing the length will increase the flow rate but may not have as dramatic an effect.
  • Each valve and fitting reduces the flow rate. If you suspect the fittings or valves, you might replace them with higher Cv (https://en.wikipedia.org/wiki/Flow_coefficient) versions.

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