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Old 11-03-2012, 19:39   #1
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Water Pump - psi vs Litres per Min ?

I guys
Am looking to put a freshwater pump in to run an out door rinse off shower and the kitchen tap. Looking on eBay reveals a lot of higher pressure 80psi plus pumps with lower output or higher water flow rate 30 litres per min etc. do I go for the higher psi or litres. Am thinking more litres means more waste ? Higher psi means stronger water pressure but smaller shower nozzle? Am I on the right track?
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Old 12-03-2012, 04:48   #2
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Re: Water pump psi vs litres per min?

You don't give enough information. What size boat do you have, how extensive is the fresh water plumbing system, and how many gallons of water do you carry? For the average cruising sailor psi rates are around 25-40psi and flow rates are closer to 12-14 liters per minute on standard type pumps. That should be enough for just a wash down and galley faucet. But if you're on larger boat those numbers mean nothing. If you're on a small boat either 80psi or 30 liters per minute is way over the top.
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Old 12-03-2012, 05:07   #3
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Re: Water pump psi vs litres per min?

Keep the pump pressure @35 psi, no more. More pressure means more chance of a burst pipe or component
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Old 12-03-2012, 05:12   #4
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Re: Water pump psi vs litres per min?

Our pump was set at 40 psi. 80 will likely blow your hose connections off.
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Old 12-03-2012, 05:56   #5
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Re: Water pump psi vs litres per min?

I don't think you are looking at freshwater pumps on EBay if you are finding 80# ones, or you are reading the spec wrong. Probably all the FW pumps can reach 80# but the pressure switch is gong to be set lower. Look at the set pressure not a rated pressure.

Far as the rate/waste most time the flow is going to be limited by the line size, length and the fitting at the end more than anything else.
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Old 12-03-2012, 06:55   #6
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Re: Water pump psi vs litres per min?

Just a note;
The spec pressure can only be maintained if the plumbing/hose is the same size, or smaller, then the pump outlet.

Flow is rated by the size of the pump outlet.
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Old 12-03-2012, 17:45   #7
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Thanks guys. Boat is a s&s 34. This will be a totally new line that I will be running straight from the water tank which is just over 110 liters. It won't be a long distance to run so I was just going to go with about 12mm hose which seems to fittest pod. I am moving aboard and the girlfriend will live aboard one week out of 3. We are in a marina so it's mainly for weekends away after a swim and to fill water bottles up etc
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Old 12-03-2012, 17:52   #8
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Re: Water pump psi vs litres per min?

Simply tee into your existing fresh water line. You dont need another pump.
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Old 12-03-2012, 18:26   #9
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Re: Water pump psi vs litres per min?

@cheechako - I dont have a pump at all. Just a hand crank one which is difficult when washing hands etc and annoying me :-)

@donlucas - Here is a 100 PSI one on ebay 12 VOLT WATER PRESSURE PUMP MARINE BOAT 100 PSI | eBay

Thanks everyone for the help. I will go with a 12.5 Litre 40psi one I think.

So much to learn!!! I have only had the yacht a few weeks and am having a ball. Lots of work still to do.
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Old 12-03-2012, 18:37   #10
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Re: Water pump psi vs litres per min?

You're gonna love that stern shower....
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Old 12-03-2012, 19:00   #11
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Re: Water pump psi vs litres per min?

Quote:
Originally Posted by Mattyb View Post
@
@donlucas - Here is a 100 PSI one on ebay 12 VOLT WATER PRESSURE PUMP MARINE BOAT 100 PSI | eBay
Yes there is and I never said such a thing was not possible. Of course that is just the pump and no specs are given as to a pressure switch.

Go ahead and get it if you really believe a 100 PSI pump is what you want.
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Old 12-03-2012, 19:23   #12
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Oh I wasn't having a go at ya! Was just saying that was what I was seeing. I know what you mean. I am going a 35psi 12.5 liter per minute one I have found. Will Ron 12mm piping throughout which is what the pump connections are sized at
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Old 12-03-2012, 20:04   #13
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Re: Water pump psi vs litres per min?

Just a quick note that most land side plumbing products are rated for 80 psig max. Generally plumbing codes (usa anyway) list max working pressure at 80 psig. For a Boat with some hose clamp connections, 40 psig is the maximum I would use.
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Old 13-03-2012, 06:09   #14
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Re: Water pump psi vs litres per min?

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Our pump was set at 40 psi. 80 will likely blow your hose connections off.

Just to play the devils advocate here, your hoses and fittings should be able to withstand 80psi and more without blowing off. If they can't withstand 80psi it won't be long before 40psi will take them out as well.
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Old 13-03-2012, 10:15   #15
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Re: Water pump psi vs litres per min?

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Just to play the devils advocate here, your hoses and fittings should be able to withstand 80psi and more without blowing off. If they can't withstand 80psi it won't be long before 40psi will take them out as well.
As a note; just make sure the hoses and barb fittings are a good match (snug fit), and that you use 100% SS clamps, doing a quarterly maintenance of tightening the clamps using a hex driver (not screw driver). The first 2-3 times you'll notice a little more squeeze but after that it will limit out.
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