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Old 28-01-2008, 13:30   #1
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Fresh water pump - How many GPM?

Im going to go ahead an replace my old freshwater supply pump. The one I have is about 30 years old and loud as all hell. I was wondering what a good GPM rating would be for a 41' boat with 3 sinks and a water heater would be. I would likely only run 1 sink at a time, though. Would 3.4 GPM at 30psi be good enough?
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Old 28-01-2008, 15:51   #2
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I just replaced a pump this week. I won't go back to anything other than belt driven pumps any more. It makes the pump unit seperate from the motor. I think they run quieter than the other ones that sound like a vibrator. I think the 3.4 GPM is fine. The one I replaced did that (til it died after a year). Anything more than that and a few teenagers will drain the tank in a hearbeat. Just be sure to add an accumultor pressure tank. Even the cheap Jabsco for $60 is better than nothing.
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Old 29-01-2008, 02:39   #3
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Some pumps are coming with instructions saying they don't need accumulator tanks. I have found a big benefit in still having the tank.
I have jut gone from a 12ltr/min pump to a 17ltr/min pump @ 45PSI. It is aweome flow and pressure, but Paul is right. A frightful amount of water can be quickly wasted if you are not careful.
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Old 29-01-2008, 04:01   #4
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Whichever pump capacity you buy, make certain the pump is a self-priming diaphragm (run-dry) type, c/w auto-reset thermal overload protection.
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Old 08-02-2008, 19:00   #5
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My freshwater pump has also just bit the dust. I know it is old but I think I may have contributed to its demise when I shocked the water tank. I think I put to much bleach in the tank and the bleach killed the diaphragm; even though I waited a few days before i pumped all the water out. So, I have three questions.

1. What is the proper way to shock a water tank(170gal) so that the water is safe to consume and you don't damage the freshwater system?

2. How often should you shock the tank in a sub-tropical climate(Florida).

3. What brand/model water pump is the best for a 42 sailboat with 3 sinks and 2 showers. (or at least give me a ...whatever you do don't buy this pump...)
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Old 09-02-2008, 00:58   #6
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3.5 GPM should be plenty considering that the low-flow residential showerheads and faucet aerators that are now required in places with water shortages like Southern California are 2.5 GPM. Not really any water shortages there, just people surpluses, but I digress.
I have the typical Jabsco or ShurFlo pump, but next time it breaks down, I think I will replace it with one of the belt driven ones. The Jabsco or ShurFlo can be found at any RV parts place for about $70, or you can get the same thing at West Marine for $200. They work OK, but don't seem to have a very log lifespan - I have sevar broken down ones from both the boat and my RV.
The accumulator tank is highly recommended - keeps the water pressure constant, but the best part is that you don't have to listen to that stupid pump everytime you crack the faucet for just a thimbleful of water.
Beware of those new pumps that say they don't need an accumulator - they are incompatible with accumulators. Actuall will work, but very poorly.
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Old 09-02-2008, 05:07   #7
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Salty dog as far as shocking your tank. You only need to do it when you need to so I wouldn't say it has to be done regularly. Yearly might be more than enough. As long as there isn't light getting into the tank it will stay clean along time. The chlorine in city water will allow it to stay fresh quite long. It might start to taste funny long before it is unsafe. Just flushing with City water will do a lot.

When you do shock it you are killing a few germs not making it clean inside. The municipal drinking water system uses Chlorine and you don't generally smell or tastes it at that level (OK some folks can). So the basic rule is once you can begin to smell it coming out of the faucet it's enough. I used to have the concentration written down but just a guess from memory would indicate maybe 8 ounces for 170 gallons.

Add the bleach then dilute to fill the whole tank. Turn on everything until you can smell it coming out of all outlets. Come back the next day and drain the tank 100%. Next maybe add 20 gallons and pump that out repeating until the taste is gone and if you really want to fill and drain one more time and it should be done. The goal is to kill not to "clean".

Your tanks and lines can accrue mineral deposits that can harbor elements that can alter the taste. To get rid of that takes strong chemicals and that process is far more complex unless you don't mind drinking toxic chemicals. Putting them in is easier than neutralizing them and cleaning them out as well as the sediments they create. Opening up the tank is really the only way when it gets that bad.

If you dumped down a gallon or two of bleach it would start to degrade the system, but I doubt it would destroy it. If my guess was totally wrong the right number might be 16 ounces but clearly no more and maybe less. More added really won't kill them "more dead".

I just installed a belt drive pump and then set about winterizing the water system. Never drank a drop from it yet. I can tell you how great it is in late March or April. They cost about double under $400. The pump head is much like a March circulating pump I use on the A/C system. It means you can disassemble the pump head and do things to it. You can also just buy a spare head.
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