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Old 02-08-2016, 22:05   #1
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Freshwater Pressure Pump replacement sizing

Hello everyone

New to me forum, new to me yacht, new to me systems to work out.

I was informed that the water pump was cactus prior to purchasing my yacht.

The pump was a Shurflo 11lpm (3pgm) pump.

I was simply going to replace it, but then thought about the previous owner/builders 'almost complete' shower recess and deck shower.

Anticipating these being operational, would it be worth shifting up to the next size Shurflo (15lpm)?

3gpm says up to 3 outlets - AU$260
4gpm says up to 4 outlets - AU$450

...Big price jump for an extra 1gpm or 4lpm, but happy to spend if worth it.

Is there that much difference in real world pressure at the faucet?

I assumed that the 'up to 3 or 4 outlets' means running concurrently? If so, this would rarely happen anyways...rarely. But, would I need the extra grunt to get the water flowing better 6 feet above deck height?

Or, would the extra grunt and pressure only become noticeable if and when I run the outlets concurrently?

I understand the laws and relationships between pressure, volume, distance etc.

Looking forward to your opinions and feedback.

Thanks
Jase in Australia
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Old 03-08-2016, 02:07   #2
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Re: Freshwater Pressure Pump replacement sizing

If your old pump gave you adequate flow rate and pressure, I would say do NOT upgrade it. You may significantly increase your water consumption. Galley foot pumps are so effective at saving water just because of this effect.

I just changed a nominally 4 gph pump for a 5.2 one, which is also quite a bit higher pressure (it was a washdown pump). The shower is now really pleasant as the water really gushes out. The higher pressure improves delivery to distant fixtures. But the increase in water consumption is really noticeable. This includes hot water, which used to be enough for two decently luxurious showers one after the other, but is now not enough for two gusher showers.

So keep all that in mind when you choose your next pump.

I will probably install a separate pressure switch which allows me to regulate the pressure and turn it down.

Another tip --

The Jabsco Par Max which I just replaced only lasted about 5 years, and seemed badly designed when I took it apart. I replaced it with a Johnson pump, made in Sweden, which seems much better quality, and which makes a really high-quality sound.
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Old 03-08-2016, 02:21   #3
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Re: Freshwater Pressure Pump replacement sizing

Quote:
Originally Posted by Dockhead View Post
If your old pump gave you adequate flow rate and pressure, I would say do NOT upgrade it. You may significantly increase your water consumption....
Thanks for that!

I'm not sure how satisfactory the old one was...it wasn't working when I purchased the yacht. He said it worked 'ok', but in considering the final touches yet to be completed on the yacht (cabin shower and deck shower), I thought it wise to anticipate those as well.

As far as water consumption goes, I'm not overly concerned. I have 120 gal / 450 litres of water across 2 bladders. Plus, the showers, while installed, will only be used occasionally, and I'll be enforcing the 'egg timer rule' on both my daughters!

Thanks for the tips!

Jase
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Old 03-08-2016, 02:56   #4
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Re: Freshwater Pressure Pump replacement sizing

I have a 3gal/min fresh water pump, and have found that perfectly adequate for the boat.
It may be on the very rare occasion that two outlets are opened at once (usually a mistake, and results in lots of hollering if the GF is taking a shower)
If it was me, I would stick with the lower volume unit and save the money.
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Old 03-08-2016, 03:07   #5
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Re: Freshwater Pressure Pump replacement sizing

Dokhead's right. See his previous discussion, where a lot of us chimed in about this subject.

If you can't find it, I'm sure he'll be glad to help you locate it.

Good luck.
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Old 03-08-2016, 08:38   #6
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Re: Freshwater Pressure Pump replacement sizing

When the water pump installed by the manufacturer packed it in, I replaced it with the next size smaller, mostly to save money. It was quite a lot cheaper. And I was very pleased to find that the flow was slightly reduced, but still adequate for all practical purposes, so there was a significant reduction in overall fresh water usage.
Of course, at some point, if the pump size were reduced further, the flow would become inadequate, so one cannot extrapolate this tactic without limit.
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Old 03-08-2016, 08:41   #7
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Re: Freshwater Pressure Pump replacement sizing

Before you increase anything: I have learned to check every valve, fixture, pipe joint - plus the electrical supply (wire size, breakers) ability to run a component larger than original to the system. I don't know your situation but I've learned the hard way to consider anything installed by original equipment designer or builder probably was probably sized no bigger than needed.

I have had excellent luck with Jabsco 3.5 GPM diaphragm pumps for fresh water supply. We shower and run another tap often. I got 14 years out of the last one before rebuilding the belt and rubber bits. Still going strong.
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Old 03-08-2016, 08:49   #8
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Re: Freshwater Pressure Pump replacement sizing

Pressure drops through both the suction and pressure side will impact flow from the outlets.

If the pump works then look for large pressure drops. Starting on the suction side. Look for undersized hose, sharp bends, poor flow fittings, etc.

Measure flow directly from the outlet to see how much flow loss your suction side has.

Then measure flow from your outlets. Address the biggest losses first.

Much cheaper to address poor routing, incorrect hose size, poor flow fittings than just throw another pump at the problem. Upsizing may have no impact other than to empty your wallet.

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Old 03-08-2016, 08:56   #9
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Re: Freshwater Pressure Pump replacement sizing

Before parting with the big buck$, start out buying a pump rebuild kit and give that a try. It should cost about $30 which might be money well spent. You will also learn how that pump works.
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Old 03-08-2016, 09:04   #10
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Re: Freshwater Pressure Pump replacement sizing

I also bought an older boat with a questionable, currently non-working fresh water pump. I plan to take it apart to lube the motor bearings and perhaps replace any diaphragms, etc. that might be needed. I'm hoping there are still parts available.
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Old 03-08-2016, 10:19   #11
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Re: Freshwater Pressure Pump replacement sizing

Quote:
Originally Posted by jasonquick View Post
Hello everyone

New to me forum, new to me yacht, new to me systems to work out.

I was informed that the water pump was cactus prior to purchasing my yacht.

The pump was a Shurflo 11lpm (3pgm) pump.

I was simply going to replace it, but then thought about the previous owner/builders 'almost complete' shower recess and deck shower.

Anticipating these being operational, would it be worth shifting up to the next size Shurflo (15lpm)?

3gpm says up to 3 outlets - AU$260
4gpm says up to 4 outlets - AU$450

...Big price jump for an extra 1gpm or 4lpm, but happy to spend if worth it.

Is there that much difference in real world pressure at the faucet?

I assumed that the 'up to 3 or 4 outlets' means running concurrently? If so, this would rarely happen anyways...rarely. But, would I need the extra grunt to get the water flowing better 6 feet above deck height?

Or, would the extra grunt and pressure only become noticeable if and when I run the outlets concurrently?

I understand the laws and relationships between pressure, volume, distance etc.

Looking forward to your opinions and feedback.

Thanks
Jase in Australia

Updated my Jabsco Pump from 3 gal. to 4 gal / min to get a better pressure for my water system
Had to change the size of the suction pipe in the water tank to make up for the higher flow .The pump was running very noisy trying to suck more
water out and creating a vacuum.
Cheers
Siggi
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Old 04-08-2016, 08:17   #12
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Re: Freshwater Pressure Pump replacement sizing

My present boat had a belt driven water pump. I replaced it with a smaller multi-diaphragm direct drive pump. Its quieter, and completely satisfactory.
The smaller pump in your case will be fine, and will likely reduce water consumption. 120 gallons sounds like a lot, but it can go pretty quick.

A friend of mine almost emptied my 40 gallon tank doing dinner dishes.
And Darlene uses a LOT of water when she washes her hair.
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Old 04-08-2016, 08:38   #13
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Re: Freshwater Pressure Pump replacement sizing

I bought a spare Jabsco 36800 pump last year for a trip, but instead of replacing I rebuilt the old one. Now I am selling the new pump, still in unopened box, on eBay for $379 if you are looking for complete replacement. That is cheap.
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