What capacity pump?

[Gwylan]

Our fresh water pump finally died and I've spent the last 3 weeks pumping any water that was needed.

Bit of a pain but keeps you fit and keeps down the water consumption.

Anyway, now I have to choose a new pump.


The cold water tank is 400 litre capacity and we have a 40 litre hot water tank - heated via the engine cooler system.
We have 3 outlets, including one that doubles as a shower. Only usually 2 of us on board.

What capacity should it be?
Any suggestions for make,

 

[rob2]

What size was the old one? You want to match it or increase the capacity if you found it inadequate.

Simples!

Rob (with a foot pump)

 

[Gwylan]

What size?

What size was the old one? You want to match it or increase the capacity if you found it inadequate.

Simples!

Rob (with a foot pump)

Well the old one is buried in the bowels of the boat and is not immediately accessible. Serious understatement here - the hot water tank will have to come out and the pipework dis-assembled, along with the locker containing said tank and the existing filters etc

Also I'd like to understand how these things are sized.

 

[VicS]

I'd like to understand how these things are sized.

I think you will find it is according to their maximum pumping flowrate against no back pressure.

I cannot say I have seen any info on how that flow rate is affected by back pressure on the outlet which in the case of a shower will be due the height of the shower head above the water level in the tank.

They are usually diaphragm pumps so wont be affected to the same extent that an impeller pump will be but bound to be affected to some extent.

The minimum size of pump you will require will depend on the shower head you have.

 

[Billjratt]

Well the old one is buried in the bowels of the boat and is not immediately accessible. Serious understatement here - the hot water tank will have to come out and the pipework dis-assembled, along with the locker containing said tank and the existing filters etc

Also I'd like to understand how these things are sized.

How the Hell do you maintain it then? Maybe there's a simple problem with the existing pump which you haven't taken the time to investigate.
Time for a re-design - possibly re-using the original pump if you're lucky. Put it up beside the filters and accumulator.
If you get a leak down there as it is, you'll dump all your freshwater in the bilge and be unable to do anything about it.

 

[Martin_J]

If it helps.. I have similar size water tanks, two heads (both with hot showers), galley with hot water, outside hot shower.. ..

but, back to the point.. My pump, a sureflow diahragm pump (2088-423-343) 30PSI, 2.1BAR, 10.6 l/min, 12v is enough for a good shower!

Surely all boats whatever size will have similar water pump pressure requirements. As others have said though it will be worthwhile using a single hose from the bottom of the tank to somewhere more accessible for the pump - then mount it on thick rubber washers (usually supplied) to make it quieter. I am sure there are quieter pumps around than mine - just throught the flow rates and pressure ratings might help. A suitably sized accumulator will also help to even the 'partially open tap' flow rates if not already fitted.

 

[stuhaynes]

Our fresh water pump finally died and I've spent the last 3 weeks pumping any water that was needed.

Bit of a pain but keeps you fit and keeps down the water consumption.

Anyway, now I have to choose a new pump.


The cold water tank is 400 litre capacity and we have a 40 litre hot water tank - heated via the engine cooler system.
We have 3 outlets, including one that doubles as a shower. Only usually 2 of us on board.

What capacity should it be?
Any suggestions for make,

Apart from a problem with the pressure switch (fixed FOC) we're more than happy with our Johnson 5.2 GPM @ 42 PSI. We had a pathetic Shurflow before and ditched it as useless. It would not feed more than one tap without scalding/freezing the person in the shower when a second tap was opened. I think we paid £110.00 for the Johnson. Better to go OTT and have a bit of peace of mind. IMHO

 

[Jegs]

Water pressure

It might be worthwhile to check the rating of pressure relief valve on the hot water tank before selecting the pump.

John G

 

[Gwylan]

very good point

It might be worthwhile to check the rating of pressure relief valve on the hot water tank before selecting the pump.

John G

Think that we have to service that whilst all the other stuff is out and it might be significant to the whole system

 

[pappaecho]

Work on the basis that there are only two sizes of pumps. Too big and too small.. if you look at the Jabsco Par range of pumps, they give general sizing information based on the number of outlets. A larger capacity pump is less stressed, and the current drain is marginal as compared witha smaller pump. I havea similar setup to you and I have a Par 3