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Old 09-10-2015, 12:16 AM   #1
JEP
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Fresh water pump question

I have a 2.8 GPM, 7.5a, 45 psi shurflo fresh water pump on my 34' mainship. I have two baths and it seems if something is on there is no water pressure.

I would like to replace it to increase the water pressure. I have looked at several but I'm not sure if I need to increase the PSI or GPM.

Also at what increase in pressure should I start worrying about blowing fixtures off.
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Old 09-10-2015, 12:32 AM   #2
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A good quality fresh water system should be good to at least 50 psi.
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Old 09-10-2015, 07:01 AM   #3
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Perhaps the sypply lines are too tiny?

I install 5/8 flaired copper tubing on new builds and find a small low pressure pump does fine.No washer or dishwasher tho.
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Old 09-10-2015, 07:47 AM   #4
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Quote:
Originally Posted by JEP View Post
I have a 2.8 GPM, 7.5a, 45 psi shurflo fresh water pump on my 34' mainship. I have two baths and it seems if something is on there is no water pressure.

I would like to replace it to increase the water pressure. I have looked at several but I'm not sure if I need to increase the PSI or GPM.

Also at what increase in pressure should I start worrying about blowing fixtures off.

You might mention whether your freshwater plumbing installation uses PEX tubing or not. Mainship would have switched to that (along with other Luhrs Group units), probably with Flair-It connection fittings, but I'm not sure about when...


(What year is your Mainship? There are about three different "eras" of Mainship production... I'd guess if yours is a "motor yacht" that'd be from their "middle era" '90s?)

Anyway, a PEX installation would usually allow you some decent leeway in pressure limits...

And then too, if PEX, it'd be useful to know what diameter tubing...

-Chris
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Old 09-10-2015, 08:35 AM   #5
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Switch to a 4 gpm pump.
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Old 09-10-2015, 09:03 AM   #6
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Switch to a 4 gpm pump.
+1.

You need more flow, not more pressure, assuming there is no restriction in your fresh water system. Even with a restriction, the higher capacity pump will partially compensate.

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Old 09-10-2015, 10:01 AM   #7
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Agreed. To understand why, think of a hose nozzle with multiple output patterns (spray, soaker, mist, etc.). The pressure at which the water exits will be higher or lower depending on the pattern you select but the time it takes to fill a bucket will always be the same because the quantity of water exiting the nozzle for a given period of time doesn't change (that's the flow).

I had a 4 GPM pump but when it broke I replaced it with a 2.8 simply because I find that I waste less water that way and I don't have to refill the water tanks as often. But if you need more pressure in your system, a 4 GPM is your answer.
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Old 09-10-2015, 10:10 AM   #8
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"I had a 4 GPM pump but when it broke I replaced it with a 2.8 simply because I find that I waste less water that way and I don't have to refill the water tanks as often. But if you need more pressure in your system, a 4 GPM is your answer."

Or, buy a crappy Home Despot galley faucet like I did and then discover the aerator is not removable for cleaning. Before you know it you will never have to fill your tanks.

As the pirate said, "AARRG."

Howard
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Old 09-10-2015, 01:34 PM   #9
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Keep in mind when you increase flow, you increase volume, meaning your 6 gallon hot water heater will run out faster.


I have 2 inline whole house water filters feeding a FloJet Sensor 4.5gpm, with 45psi diaphragm pump that feed a storage pressure tank.


The water pump actually does better than city water.
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Old 09-10-2015, 08:49 PM   #10
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Thanks to everyone on the help. I think the consensuses is 4 gpm and 50 psi. This has been great responses
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Old 09-10-2015, 09:41 PM   #11
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You should go to a VSP which is a variable speed pump, I changed ours after issue with the accumulator tank. The VSP means you can eliminate the accumulator tank and when multiple faucets are opened the pump adjusts automatically.
They are a little pricy but works well, we use ours everyday as I don't use a dock faucet for pressured water and just fill our tanks as needed, roughly every two weeks as liveaboards.
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