Water pump for hot water unit

Submitted: Saturday, May 01, 2010 at 22:30
ThreadID: 78153 Views:2504 Replies:3 FollowUps:4
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Hi folks,
I have a question re my newly aquired Mercury instantanious hot water unit. It is rated at 6 litres per minute, and I have to choose the 12 volt water pump to go with it. Considering the water heater's rating, would it make any difference what PSI/Litre per minute pump I chose? By that I mean, would I get a stronger flow out of the shower rose/sink tap if I chose say a 60 PSI/17 litre per minute unit over a lower output model?
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Reply By: Member - mazcan - Saturday, May 01, 2010 at 23:12

Saturday, May 01, 2010 at 23:12
hi smokeyd
yes it would but you'd also use twice as much water
but you'd be asking for trouble

to put a pump on your instant hot water system thats rated twice what the unit flow rate is would in my honest opinion probably blow it apart or put unnecessary strain internally and cause premature failure

shurflow make a small pump about 5.5l/per min which would ideal
AnswerID: 415054

Follow Up By: SmokeyD - Saturday, May 01, 2010 at 23:37

Saturday, May 01, 2010 at 23:37
Hi mazcan,

Oh, ok - understand your point. Just worried about pressure under the shower, don't want to have a pathetic dribble at the rose considering the height it has to pump (ie head height).
FollowupID: 685236

Follow Up By: Crackles - Sunday, May 02, 2010 at 00:29

Sunday, May 02, 2010 at 00:29
My understanding is the Mercury unit can be connected into a house on mains pressure so doubt any 12 volt pump would be a problem.
At one of the 4x4 shows they were running an 11L per min pump.
Cheers Craig...........
FollowupID: 685239

Follow Up By: Member - mazcan - Sunday, May 02, 2010 at 15:35

Sunday, May 02, 2010 at 15:35
hi smokey d
your response of

ok- ok i understand your point

is not what i was expecting as i was simply giving my honest answer to your question
you never said the unit in question was capable of mains water pressure so i was giving my honest opinion based on facts presented

the pump i recommended is the same as i used on a farm spraying unit

and it had enough pressure to squirt water 3mtrs accross the ground at weeds out of a spraygun nozzle on the end of a 10mtr hose

so i hope this will alay your fears of not having enough pressure at the shower head

these pumps last for a very long time i bought it in'84 and now use it on my present camper trailer which i connect to a free standing shower and primus water heater hope this has helped you in some way
have a good day from here on in
FollowupID: 685287

Follow Up By: SmokeyD - Sunday, May 02, 2010 at 23:50

Sunday, May 02, 2010 at 23:50
Hi Mazcan,
Um - if you look at my first reply to you I actually said "Oh, ok - understand your point." Nothing terse meant in that reply at all - and I didn't know that the units could be hooked up to mains pressure, as I bought what I thought was a hot water unit for camping, as it was advertised. So I appreciate your reply as I do all who give their time for others a little less knowledgeable.
Thanks again.
FollowupID: 685341

Reply By: Crackles - Saturday, May 01, 2010 at 23:42

Saturday, May 01, 2010 at 23:42
Pump size will not greatly increase the flow out of the unit as it has it's own regulator (Water dial on the right). A higher flow (17L) would be pointless as it would barely come out luke warm. The arbitrary 6 litre rating is for a 25 degree increase in water temp so if the water is cold to start with the flow may need to be as little as 3 litres per minute to get it hot enough for a shower.
Cheers Craig.......
AnswerID: 415057

Reply By: Ozhumvee - Sunday, May 02, 2010 at 09:33

Sunday, May 02, 2010 at 09:33
We've had one of those hot water heaters working in shed for a few years now and even on mains pressure it can heat the water far too hot for a shower if set incorrectly with gas versus water flow.
So I wouldn't worry about any pump being too strong for it or pushing too much water.
A bigger consideration is how much water you can use in a short time when camping.
I've tried it on very setting from a slow dribble on the garden hose to full pressure and it works well with its rated capacity of about 6l/min. You can have a good shower with 3l/min but if flow drops below that the heater turns off.
I'd get a pump of about 5-6l/min as the best. You still need to turn water off when sopaing up or you will quickly get through 20l+ in a 3 min shower.
1996 Oka Motorhome

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