Water Pump Question

[ab1985]

I'm putting together an onboard water setup for my 4Runner. I've got everything and want to install it later this week, but one question I need to address is where to mount the water pump. I've relocated some things on the driver side wheel well under the hood to make room for the heat exchanger and I've got plenty of space, but I'd rather keep the pump inside the vehicle. It's a 3.7 GPM variable speed Jabsco and instructions say it can lift water 9 ft but I'm not sure how that equates to horizontal distance. If I mount it in the rear of the truck it will pull water from the tank 2-3 ft away (where the spare used to be), pump it 8 ft forward to the heat exchanger, then 8 ft back to the faucet. If I mount it under the hood it will pull water from the tank in the rear 8 ft away, push it through the exchanger 1 ft away, then push it 8 ft back to the faucet. I contacted Jabsco and Shurflo and neither was very helpful.

What say you, expo? What needs to be taken into consideration when laying out your tank, pump, heat exchanger, and faucet locations as far as distance and pump capability?

Thanks!

 

[REasley]

The 9' is vertical lift. You're best off keeping the pump closer to the tank. The run from the pump to the heat exchanger and back is only impacted by friction loss. At 3.7 gpm your loss to friction with 3/8" hose will be around 9 psi per 10', with 1/2" that drops to about 2.4 psi. If you bump the hose up to 3/4" the friction loss drops to less than .3 psi.

 

[ab1985]

Exactly what I was looking for. Thanks!

 

[Xterabl]

yes, great info, REasley!
Quick question for you: are you referencing ID's or OD's?
Because, I have been doing the same calculation (I too am running water from back of truck to flat plate HE under hood, than back again) and my calculations indicate ~1.3 psi (comapred to your 2.4 psi) per 10' for 3.7 GPM and 1/2" ID hose. (I am using 1/2" ID Tygon hose from mcmaster-carr).
Now, this is not my forte, for sure--and I would definitely defer to your #'s; but I believe I was fairly rigorous WRT reynolds numbers, friction coefficients, etc.
And so, I was hoping you could help with this apparent discrepancy