Dual pump fresh water system

[Russ Calasant]

Does anyone have an understanding of how exactly the dual pumps work or are supposed to work together? What is the idea behind two pumps and how should they be adjusted?

 

[dtfeld]

Are you refering to fresh water pumps?

If so, the limiting factor is how much water a pump can move in gallons per minute (GPM) Doubling them up in parallel, doubles the max flow rate.

 

[NotHerDecision]

I have the dual pump system. They do work together well but I have found the following to be true.

If you have an accumulator just get rid of it. There is no need.

If you replace a pump it’s best to replace both but if you do one then buy an exact pump for the second one.

There is a tiny Allen head screw on the end of the pump to make adjustments. You really have to be patient and fiddle with these when you have dual pumps to get them close.

 

[The Bill Collector]

Does anyone have an understanding of how exactly the dual pumps work or are supposed to work together? What is the idea behind two pumps and how should they be adjusted?

My understanding is that with all the outlets & to keep up with potential demand they installed 2 pumps so water pressure wouldn't turn into a dribble... I have had the boat 11 years and have never adjusted them, so no comment there.

 

[quality time]

As far as I know they both only come on when needed. Only one runs if the demand isn't high enough.

 

[ttmott]

The pump pressures should be offset (one set to come on at a lower pressure than the other). You can set them up to your preference but start with one set to come on at say 50 psig and the second to come on at a point slightly lower like 40 psig. Tailor the lower pressure one as you see fit so the water does not surge up and down but they are not triggering each other on and off using your highest demand faucet or shower. An accumulator will further dampen the surging as well as reduce the start and stop frequency of the pumping system. If you attempt to set the two at the same pressure they will "fight" each other cycling on and off rapidly and end up failing prematurely.

 

[Russ Calasant]

The pump pressures should be offset (one set to come on at a lower pressure than the other). You can set them up to your preference but start with one set to come on at say 50 psig and the second to come on at a point slightly lower like 40 psig. Tailor the lower pressure one as you see fit so the water does not surge up and down but they are not triggering each other on and off using your highest demand faucet or shower. An accumulator will further dampen the surging as well as reduce the start and stop frequency of the pumping system. If you attempt to set the two at the same pressure they will "fight" each other cycling on and off rapidly and end up failing prematurely.

Thank you all for the info. Ttmott, how do I do that? Open a single outlet and adjust one pump to activate then open another outlet and adjust the second pump to trigger? Does it matter which pump? I have never been able to adjust properly and now can’t seem to get pump 2 to trigger at all. I have ordered two new pumps and will try again. I appreciate the input.

 

[ttmott]

Thank you all for the info. Ttmott, how do I do that? Open a single outlet and adjust one pump to activate then open another outlet and adjust the second pump to trigger? Does it matter which pump? I have never been able to adjust properly and now can’t seem to get pump 2 to trigger at all. I have ordered two new pumps and will try again. I appreciate the input.

Need first to install a pressure gauge somewhere in the system so you have something to adjust the pressures to. First electrically disconnect the pump for the higher pressure and then set up the low pressure pump cut-off pressure; then switch the pumps electrically and set the cut-off pressure for the high pressure one. You will probably need to spend some time with the low pressure pump settings to get a good cut-in overlap with the high pressure pump. Re-thinking the pressures maybe better to have the high at 55 psig and the low pressure closer at 5 PSI lower.

 

[techmitch]

The pump pressures should be offset (one set to come on at a lower pressure than the other). You can set them up to your preference but start with one set to come on at say 50 psig and the second to come on at a point slightly lower like 40 psig. Tailor the lower pressure one as you see fit so the water does not surge up and down but they are not triggering each other on and off using your highest demand faucet or shower. An accumulator will further dampen the surging as well as reduce the start and stop frequency of the pumping system. If you attempt to set the two at the same pressure they will "fight" each other cycling on and off rapidly and end up failing prematurely.

Couldn't agree more about the importance of an accumulator, especially in larger boats with multiple water supply needs/outlets
and dual pumps.
The function and benefits of the dampening and surge control are often overlooked and sometimes deemed unnecessary then removed/bypassed. The R&D guys and the bean counters at the end of the production line would had had a serious pissing match if the accumulator was not figured to be of the upmost importance to achieve regulated, plentiful and steady water pressure and volume at any given time or place on the boat.

 

[NotHerDecision]

I can’t see one benefit in an accumulator. I have dual pumps with the pressure set near one another. Invariably one pump always comes on first but at higher demand both come on. There is no surging and the pressure is great. The one caveat is this. I have replaced both with higher pressure/more volume pumps. I think they are 5gpm but I’m not currently at the boat.

 

[mwph]

I have no tank so no real experience here, but the comments from Techmitch about the purpose & need for a tank, along with others mentioning fewer pump cycles leading to extended pump life make a lot of sense to me. I seriously doubt boat manufactures install items just for the hell of it.