Water pump

ct0218

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Our mountain lakes are quite cold except for a short time in the middle of summer, so I plan on adding a water pump and tankless water heater for use as a shower system on board. When researching pumps, I found both RV/boat water system pumps and boat washdown pumps. I asked at several boat dealers and none had a clue which type pump I needed. The heater requires a diaphragm water pump producing a minimum of 35 PSI at 3.5 GPM. Since I'll be pumping out of the lake, it will need to be a self priming pump. Does anyone know the difference between the two pumps, and which I would need?
 
My personal research, a "washdown" pump is typically more for short term use. An "RV/Marine" pump is rated for continuous use.

RV pumps may also have a check valve for high pressure protection if system is hooked into a supply with high pressure. I would lean toward RV/Marine pump, and don't skimp........
 
I think I would go to an RV dealer and see what they recommend or what's used in an RV.
 
I know that a RV demand water pump meets the requirements, but nowhere can I find info telling me if it will self prime. I know that in my fifth wheel I have had a problem with the demand water pump priming when using the fresh water tank. Not sure why it is sometimes a problem, but it is. That is what made me wonder if it would prime and pump on its own. The only way to get around the self priming requirement is to mount the pump slightly below the surface, and since the pontoon has yet to be delivered, I'm not sure if there is a place to mount it like that. Or, possibly a check valve at the end of the pick-up hose would work. My fifth wheel has a 5.7 GPM constant pressure pump that doesn't require an accumulator tank to even out the pressure, so there is no pulsing with it.
 
Marine pumps may also be more for "wet" locations, where RV pumps are for dry ??

I don't think they are meant to be mounted "below" the surface, that's only bilge/live well pumps .... To my knowledge ..... which is limited ... :)

I have a portable washdown and it's self priming and only takes a couple seconds to prime.
 
Self primes, but the flow is the problem---1--3.2 GPM  @ 35 PSI. I need 3.5 at a minimum. I'll see if Flojet has a model with a little higher flow. Digging a little deeper I see that the main difference between a washdown marine pump and an RV water system pump is the rubber material used in the pump diaphragm--a washdown pump utilizes a rubber material (nitrile) not suitable for drinking water. A water system pump uses Santoprene and EPDM elastomers.  That is not a problem, just used for showers, so it appears that either pump will work. Just two of us most of the time, times one shower a day, times X days...shouldn't be a problem for a quality pump! That being the case, this should work--Jabsco Par-Max 4, # 362050092, 60 PSI, 4 GPM.
 
Bamaman, I totally agree. I shower at home with a lot less than that. However, I went to the website for the tankless heater (Camp Chef Triton 10L) and viewed the owners manual and it said on page 9 that when using this heater with a pump that it needed to be "at a minimum an on-demand diaphragm 3.5 GPM pump". I wish it required a little lower volume, these pumps are priced by volume and pressure ratings, and it would save me a few bucks.
 
Be sure and do not buy a Harbor Freight marine pump. I have bought three and they last about 15 minutes and then stop pumping. Will spend three times the money and get a better pump. Steve
 
So true...I was looking at Flotec and a Jabsco, I've had good luck with both over the years.
 
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