Water pump ratings?

I looked at several kart suppliers and none of them list the gallons a minute at X rpm for axle driven pumps.

I need to pump 3 gallons a minute at 2200 rpm and I’d rather not use an electric pump unless necessary.

Do you have a cordless drill, some 5-gallon buckets and a stop watch?

High speed on the drive side, 1min and check the volume moved. Water weighs 1kg/liter or 8.34lbs/gal if you have a scale and want to be accurate.

(If I recall correctly, most standard cordless drills on high speed run around 2000-2500rpm)

I don’t have an answer but I’d love to know the application.

Edit, nevermind I just put two and two together :joy:

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Matt, I get that. I don’t currently have one to test, and don’t just want to buy stuff to test it out.

GPM at some pressure is a spec listed on any normal pump, but for some reason none are listed for any of the kart ones I’ve looked at - not even the hose size is normally listed!

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Since nobody I’ve written has any idea what the specs are on these things, I plan to buy a metal pump and test it. I’ll post the results when completed.

Hi Brian - late to the party here.

So it’s an EV built?

I would think that cooling would have more specs than GPM @ 2200RPM. I would expect that you would have thermodynamic rating as well - this rating would look similar to heat sink (thermal junction) spec on a semiconductor chip.

In short, what good does it do to supply X GPM @ 2200RPM at 120 Celsius? Nothing.

Are you cooling the motor or battery pack?

If motor, there should be an efficiency rating on it. Let say 88%. So you can assume 12% is heat (which both adds up to 100%). Now, then what’s your supply voltage? Then you can measure the current. Let say 12V at 100A - so it’s a 1200W motor.

You then know that 88% is converted to mech energy and 12% is heat. So 12% of 1200W is 144W. Now you know you need to “bleed” 144W of heat out.

For size comparison, you can look at CPU heat sink “TDP” (Thermal Design Power) spec. Many desktop CPUs are 65-95W - look at the heat sink for those CPUs.

BTW, that’s way under powered - 748 watts equal to 1 horsepower. 1200W is like 1.5hp.

Too Vira (sorry, not sure what your real name is), 2200 RPM is the top speed of the rear axle used to drive the water pump for the sprint racing track of interest - not the speed of the motor.

The motors that I have looked at that are liquid cooled need around 2 GPM at X temperature, so 3 GPM at a reasonably low pressure (motor, hose, etc dependent) is desirable since that is only reached at end of a straight. The temperature has nothing to do with the pump which is what my question was about (ratings on kart pumps), but rather the radiator and the ambient temperature so I did not include that.

Yes, 1200W is pathetic. 21kW is what I am designing for with this application. First candidate pump is on order so I can get some hard numbers.

That is my real name. :slight_smile:

Yes, you should be able to get motor efficiency (typically on the label or at worst, spec sheet). If it’s a 3 phase motor, then it’s likely 88% or higher. If it’s single phase or DC, it’ll be lower.

So you can literally multiply that percentage to the 21kW…and subtract the difference. That’s how many watts of heat you’ll need to bleed off with your cooling system (at 80%, you’ll have 4.2kW of heat to bleed off).

But it’s always better to log the Volt/Amp under load as that’s the real world number.

I just happens that I have over 20 years working in the pump industry. 10 years engineering before moving into sales. Large engineered equipment for infrastructure including stormwater, municipal water/waste water and oil and gas. I have been involved with equipment from 1000 psi at 250 GPM (LNG) to 25’ at 800,000+ GPM (Flood Control in Gulf area)

In general, for most pump applications no one worries about the pump inefficiency that is converted to heat, unless you are performing a test in a closed loop test pit. If you are testing a high pressure pump for hours and hours in a pit, it can start to get hot, which increases vapor pressure, which can impact the test. Most pumps are in open loop systems, and the heat transfer per unit time vs the volume pumped per unit time results in a fluid temperature rise so low as to be immeasurable.

Example: Lets say you have a pump that is moving 100 GPM of water at 100’ head (43.3 psi). Pump Eff = 65%. HP = (Flow x Head) / (Eff x 3960) = 3.88 HP. 1 HP is equivalent to 33,475 BTU /Hr. 35% of the power consumed is turned to heat = 3.88 x .35 x 33,475 = 45,500 BTU/Hr. But during an hour, how much fluid is pumped at 100 GPM? 6000 Gallons…which is 50,040 LBS. 45,500 BTU into 50,040 LBS of water will raise the temperature 0.1 Deg F which is hard to measure. For a given pump HP, a high pressure low flow pump will raise the heat of the flow stream more than the same HP of a different type of pump that produces a lot of flow and low pressure. For example, if you were pumping 1 GPM at 10,000 feet of heat at 65% efficiency the HP is the same. The heat rejected is the same. But the amount pumped in 1 hour is 60 gallons or 500.4 LBs. Now the heat rise is 11 Deg F!

Same HP…same Eff, different flow vs head…different fluid heat rise.

In an engine cooling system, the losses are very low. There is no static lift as it is a closed system. It is all friction. The pump is essentially running at low pressure, off the end of its curve. I would not even worry about heat added. We are probably talking about 2-3 GPM at a few psi at most. A pump of this size is going to be only 45-55% efficient.

So, lets assume the following:
4 feet head
45% efficient
SG = 1.0 (water…with a little bit of water wetter…which is the best coolant)
HP = (3 x 4) / (3960 x .45) = .0067 HP
.007 HP x .55 x 33,475 = 124 BTU per hour.

A good rule of thumb for an IC Engine is .33 / .33 / .33.
33% of fuel BTU = power output
33% heat goes out the exhaust
33% must be absorbed by the cooling system.

So if your ave HP around a lap is 25, that means 25 HP of heat in BTUs must also be absorbed by by the cooling system = 836,900 BTU/hour.

124 BTU/Hr from pump
836,900 BTU/Hr from engine

128 / 836,900 = .015%…which you can not even measure.

Same for pump HP. Say you can improve pump eff from 45% to 80% (almost impossible for such a small pump) it will only save you .003 HP. Not worth even trying.

As for pump testing, I would suggest finding an older version of the ANSI-HI test standards or any pump text.