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Old 31-01-2015, 11:20   #1
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How to choose GPM stength for new water pump

Though many will replace boat systems with similar parts, please note that I am a new boater doing a refit so have little point of reference when it comes to "what was."

I need to pick a new fresh water pump, so I'd like to know how to determine how much power I need in terms of reliable brands, gallons per minute (GPM) as well as know what new technology exists that may make me forget about old systems (perhaps diaphragm vs impeller).

I have a new electric motor going in, so no lines to a diesel are needed. I'm going compost toilet so no potty plumbing. The only possible uses I can think of is:

1. A fresh water rinse for dishes at the galley sink.
2. If I go for a dripless seal (Tides or Lasdrop), there may be a hose in/out (if that even applies to the fresh water pump.)
3. I'm opting for no sink in the head, but have plumbing set up for if I decide on that later.
4. I'm opting for solar bags/handheld shower pump and a bucket (then a sump pump), but have optional hook ups for standard head shower.

Thanks for any advice!
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Old 31-01-2015, 11:28   #2
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Re: How to choose GPM stength for new water pump

Myself, with a galley sink and a head sink, I went with a 2.1 GPM pump. It's good enough for one faucet running at one time. On larger boats some might go for a 4 or 5 gpm pump for two faucets running at once.

BTW, I purchased a new RV pump which was the exact same pump (ITT) as the small marine pump I was looking at, but I got it for $45 rather then $90.
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Old 31-01-2015, 11:39   #3
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Re: How to choose GPM stength for new water pump

sc, as always, with good advice.

You'll also note, if/when you look at the pumps available, there are GPMs AND there are pressures. Uaully the lower GPM (flow) pumps have lower pressures (35 psi) than the higher flow pumps (55).

If you have one faucet, but it's located a loooong way away from the pump, either get a higher pressure pump or move the pump closer to the faucet (thew pressure is the output of the pump).

Most pump manufacturers have this kind of info on their websites (Shurflow, FloJet, Jabsco, etc.).

Finally, you should keep it simple. Some of the new technology variable flow pumps have had "teething" problems, like the repeated failings of Jabscos in the new Catalina C355 boats (100s of them now).

Get a simple automatic pump, live with the noise (which, for many of us, is good: we know it works!) or slap an accumulator on it to reduce cycling.

SHURFLO AQUA KING II 2.0 Freshwater Pump | West Marine

Good luck.
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Old 31-01-2015, 11:54   #4
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Re: How to choose GPM stength for new water pump

Perfect advice in just two responses? I'm speechless. Thank you both as that tells me exactly what I needed to know. I hope this thread gets found by others with this exact question. Bless you both!
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Old 31-01-2015, 12:08   #5
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Re: How to choose GPM stength for new water pump

One update: What do you think of this one on Amazon for $68.38 vs the Aqua King II liked at West Marine?:

SHURflo 4008-101-E65 3.0 Revolution Water Pump:
Amazon.com: SHURflo 4008-101-E65 3.0 Revolution Water Pump: Automotive

It has the suggested higher 55 PSI, glowing reviews, and much less $$.

tks.
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Old 31-01-2015, 12:46   #6
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Re: How to choose GPM stength for new water pump

Quote:
Originally Posted by Captain Pappy View Post
One update: What do you think of this one on Amazon for $68.38 vs the Aqua King II liked at West Marine?:

SHURflo 4008-101-E65 3.0 Revolution Water Pump:
Amazon.com: SHURflo 4008-101-E65 3.0 Revolution Water Pump: Automotive

It has the suggested higher 55 PSI, glowing reviews, and much less $$.

tks.
Overkill, but it'd work.

I usually find the product I want, then I shop the price.
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Old 31-01-2015, 13:05   #7
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Re: How to choose GPM stength for new water pump

Quote:
Originally Posted by Captain Pappy View Post
...I am a new boater...
I have a new electric motor going in...
I'm going compost toilet...
1. A fresh water rinse for dishes at the galley sink.
...
3. I'm opting for no sink in the head...
4. I'm opting for solar bags/handheld shower pump and a bucket...
Seems like a manual pump would be a closer fit to your other choices., which seem quite strange.
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Old 31-01-2015, 14:11   #8
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Re: How to choose GPM stength for new water pump

If all you need is freshwater at one sink, a foot pump is a far better option and doesn't use any electricity. They pump on both up and down strokes, and the supply rate is dependent on the pumping speed, so within 30 seconds of getting used to one, you will have continuous flow at any speed with both hands free.

The one we have is made by Whale, but I don't recall its model name.

Mark
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Old 31-01-2015, 16:17   #9
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Re: How to choose GPM stength for new water pump

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Originally Posted by colemj View Post
If all you need is freshwater at one sink, a foot pump is a far better option and doesn't use any electricity. They pump on both up and down strokes, and the supply rate is dependent on the pumping speed, so within 30 seconds of getting used to one, you will have continuous flow at any speed with both hands free.

The one we have is made by Whale, but I don't recall its model name.

Mark
Agreed!

By choice, we use only foot pumps for the sinks. IMO, saves electricity (not all that much) and gives much better control over water usage than pressure systems. We do have pressure for the showers, one in the head, one on the sugar scoop. Only turn on the pump when showering. Has worked well for years. Just rebuilt the foot pump at the galley sink, after 24+ years of full time live aboard cruising on the part of the PO and then us. Never had an electric pump match that service life!

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Old 01-02-2015, 05:20   #10
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Re: How to choose GPM stength for new water pump

Foot pumps are a good idea for water conservation. Pump electricity use is pretty low, 3.5 to 5 amps for a total of 15 minutes a day, that'd be my estimate.

I found this for water conservation, too, works great, quicker immediate shutoff than turning the faucet, and can do with soapy hands.

Water Saver Idea

RV source for pumps & parts (startup screen appears empty, just scroll down)

RV Water Pumps, Filters, & Fixtures - PPL Motor Homes
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Old 01-02-2015, 05:58   #11
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Re: How to choose GPM stength for new water pump

The "WaterSense"* lavatory faucet specification sets the maximum flow rate of lavatory faucets and faucet accessories at 1.5 gallons per minute (gpm) tested at a flowing pressure of 60 pounds per square inch (psi) (common water pressure in most households). It also includes a minimum flow rate of 0.8 gpm tested at a flowing pressure of 20 psi to ensure performance across a variety of different household conditions.

* http://www.epa.gov/watersense/
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Old 01-02-2015, 07:49   #12
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Re: How to choose GPM stength for new water pump

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Originally Posted by Terra Nova View Post
Seems like a manual pump would be a closer fit to your other choices., which seem quite strange.
That's what I'm thinking.
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Old 01-02-2015, 19:52   #13
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Re: How to choose GPM stength for new water pump

Quote:
Originally Posted by Captain Pappy View Post
One update: What do you think of this one on Amazon for $68.38 vs the Aqua King II liked at West Marine?:

SHURflo 4008-101-E65 3.0 Revolution Water Pump:
Amazon.com: SHURflo 4008-101-E65 3.0 Revolution Water Pump: Automotive

It has the suggested higher 55 PSI, glowing reviews, and much less $$.

tks.
Just put one in the small boat, works fine but the flow valve lets it run for a couple of min.'s after shut off. good pressure but it is really around 40 PSI...
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Old 02-02-2015, 07:42   #14
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Re: How to choose GPM stength for new water pump

Along the lines of what GordMay was getting at, taking a quantitative approach to the answer is probably the best way to size the pump. Using imperial units, newer residential faucet fixtures are in the 2gpm range, plus or minus .5gpm, assuming the aerator is still intact. If your fixtures are older than 1992-ish, there is a chance that they could be up to 5gpm, although I would think on a boat that would be unlikely, but who knows. So decide how many of them will be running at once and size your pump for that. Short of having a family in a big boat, 2 to 4gpm at 30psi+ is probably fine for most small to mid size applications.
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