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Feed water pump

capta

.
Jun 4, 2009
4,133
Pearson 530 Admiralty Bay, Bequia SVG
We've been using a 12 volt Water Puppy (6.3 gpm) as a boost pump for our watermaker, but they do not like the back pressure from the high pressure pump (2.3 gpm) and over heat and fail after some time.
We have a 110 volt Dometic/March water cooled continuous duty magnetic drive pump (8.3 gpm) that will do the job quite nicely, but I have no idea if the back pressure will damage the magnetic drive pump.

I assume that the magnetic drive will not be affected by back pressure, as the Water Puppy was, because there is no direct drive between the motor and impeller. We have run the magnetic drive pump with the thru hull partially open and that does significantly reduce the water flow, but again, I have no idea if this will damage the pump.
We would appreciate any thoughts on this.
 
Jan 11, 2014
6,594
Sabre 362 113 Fair Haven, NY
Let me see if I understand this correctly, the Water Puppy is trying to push 6.3 gpm into a pump that can only accept 2.3 gpm?

If so the solution seems to be to reduce the output of the Water Puppy or to get a low pressure pump that has an output closer to 2.3 gpm.

It may be possible to reduce the voltage to the WP with a variable resistor, that would reduce the volume of water it could pump. A simple dimmer switch might do the trick.
 
Feb 14, 2014
5,061
Hunter 430 Waveland, MS
We have a 110 volt Dometic/March water cooled continuous duty magnetic drive pump (8.3 gpm) that will do the job quite nicely, but I have no idea if the back pressure will damage the magnetic drive pump.
A centrifugal pump will not be damaged by back pressure, as long as it stays cooled.
It will only use the Amps needed for the actual used flow.

The extra spin energy will heat up the water inside the pump head. If it stays cooled on a test, you are good to go.
Jim...

PS: You can do a slight bleed of water to cool the pump head if too warm.
 

capta

.
Jun 4, 2009
4,133
Pearson 530 Admiralty Bay, Bequia SVG
Let me see if I understand this correctly, the Water Puppy is trying to push 6.3 gpm into a pump that can only accept 2.3 gpm?

If so the solution seems to be to reduce the output of the Water Puppy or to get a low pressure pump that has an output closer to 2.3 gpm.

It may be possible to reduce the voltage to the WP with a variable resistor, that would reduce the volume of water it could pump. A simple dimmer switch might do the trick.
Thanks, but that wasn't the question and reducing the voltage would increase the amps, probably burning out the pump or wiring much more quickly. Since we have the mag drive pump, we'd rather use it. We are in Grenada under quarantine and are not allowed ashore, as are all liveaboards/cruisers, so we do not have the option to get another pump.
 

capta

.
Jun 4, 2009
4,133
Pearson 530 Admiralty Bay, Bequia SVG
Maybe a pump like this would work better, Everflo EF3000 Diaphragm/Demand WATER TRANSFER PUMP 3.0 GPM 12V Volt 60 psi

Also take a look at transfer pumps for home brewers. I found an inexpensive 12v one that I use to drain my HW tank. It was about $20 but the output is too low for your application.
What is it about the statement, "We are in Grenada under quarantine and are not allowed ashore, as are all liveaboards/cruisers, so we do not have the option to get another pump" that is so hard to understand?
 
May 17, 2004
2,925
Beneteau Oceanis 37 LE Havre de Grace
I have an aquarium filter with a magnetic drive pump. A couple weeks ago the impeller jammed and the pump stopped. The motor definitely did heat up, though no damage was done, and that was with zero cooling water flow. So I’d say go for it if it’s your best option, but do still keep an eye on the temperature.
 
Jan 11, 2014
6,594
Sabre 362 113 Fair Haven, NY
What is it about the statement, "We are in Grenada under quarantine and are not allowed ashore, as are all liveaboards/cruisers, so we do not have the option to get another pump" that is so hard to understand?
I do understand that and I have friends who are in a similar situation.

You have 2 problems, one a short term immediate one and the other a longer term problem, how to prevent this problem happening again. My suggestion deals with the long term problem not the immediate on.

Another short term solution might be to use a freshwater pump to supply the water maker. Some pumps, like the Shuffle Aqua King have a cutoff switch, if the back pressure gets too high the pump shuts down. Perhaps your freshwater system pump can be plumbed in to your water maker. It will supply water and when the back pressure gets too high, it shuts off.

If I remember correctly, you have a pump that uses a pressure tank. It must have the back pressure switch built in.

Of course if you repurpose the freshwater pump, you'll have to use a hand or foot pump to get water out of the tanks. Might be a small price to pay.
 
Jan 11, 2014
6,594
Sabre 362 113 Fair Haven, NY
Your wash down pump might also be repurposed for the low pressure supply pump. Letting the fitting leak a little might also help reduce the pressure and save the pump.
 
Feb 14, 2014
5,061
Hunter 430 Waveland, MS
@capta you can use the available March pump.:clap:

I really don't think it will heat up either.
I have 2 AC aboard that uses that March pump and the lines have been nearly blocked with algae and the Pump worked fine.

That March Pump is very well built.

By the way.....
If there is any water flow, it will cool the pump head.;)

Jim..
 

capta

.
Jun 4, 2009
4,133
Pearson 530 Admiralty Bay, Bequia SVG
Your wash down pump might also be repurposed for the low pressure supply pump. Letting the fitting leak a little might also help reduce the pressure and save the pump.
Thanks, but I don't think most wash down or pressurized water system circulation pumps are "continuous duty" pumps. They are designed for sporadic use, not hours and hours of continuous use..
 
Nov 6, 2006
8,923
Hunter 34 Mandeville Louisiana
The March should work OK but it is its kinda lowest stable flow regime. You can see from the attached flow curve that at around 2.3 GPM, it is backed up pretty far up the curve, making about 8 PSI. A test is probably in order.. The additional differential pressure should increase the flow through the motor cooling coil, so should be fine.. if it vibrates a lot or the magnet area heats too much, running it with the AC running should put it in a better run place (flow regime).
 

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