Water pump

I adjusted our water pump to operate correctly when the van is connected to EHU (ie volts = 13.8v), BUT it  then misbehaves (ie does not switch off) when not on EHU (ie volts = 12.6V).
I wonder if anyone has fitted a ‘voltage regulator’ in the pump supply so the voltage at the pump is constant ? A quick ebay search shows many v.regs or dc-dc converters at quite modest cost.
Peter M

Can you find a sweet-spot between the two settings that's acceptable,  most times it works?

Hello Paul, that ‘sweet spot’ seems elusive for me. I know some owners change to a different type of pump but that does seem an awful lot of effort.

I can't recall hearing of anyone trying this before, but be aware that you might need a bit of trial and error if you decide to give it a go.

Most voltage regulators are designed to supply a load which takes a (relatively) constant current, but a Shurflo pump (assuming that's what you have) is nothing like that. It's actually (I believe) an impulse-type pump, so it takes high current for a short period and then nothing while the diaphragm(s) return to resting position. So you would need one with a relatively high current rating - if you don't, the regulator is likely to current-limit during the time when the pump needs a lot of power, and the performance will be poor.

having had a Shurflo or Flojet pump on all my four vans ive never had a need to change anything when moving from EHU to NON and back again...what a pain that must be.

Very cold out there today .... it’s an immersed pump in the tank so don’t know what sort it is. Pressure switch is a ‘Whale’ in line type. Can only positively identify the pump by dropping tank and don’t fancy that till it warms up a bit.
One thing I can do it measure  pump current at the Pressure Switch. Also, pump sounds like an axial one rather than a reciprocating type.
Peter M

rgermain wrote:I would assume that Peter M is referring to a submerged pump! and not a Shuflo etc.
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richard

Richard i realised that, my point was that 'finding the sweet spot' may turn out to be totally elusive and that this is not something that needs to be done with a Shrflo/Flojet...its just one of the reasons why so many will have 'upgraded'.

Thinking about it further, I realise problem lies with the pressure switch and what I need for reliable operation is a roughly constant supply voltage at the switch (and then on to the pump). ‘Sweet spot’ is indeed elusive in my case !

Although a pressure switch would depend upon voltage defeats me .... should it not just switch according to water pressure ?

I think the voltage effects the impeller speed and the pressure that it can generate in the water pipes. You would think setting it off ehu would then work when plugged in, it just seems to create other symptoms. I’d say try a voltage regulator, some led drivers are 12v to 12v but may not produce enough amps?

petermcd wrote:Although a pressure switch would depend upon voltage defeats me .... should it not just switch according to water pressure ?

The pressure switch operates on pressure,the voltage and consequently the current will determine the pumps ability to produce the pressure. in turn this means if set whilst on EHU and its derived 12v supply which will be strong and steady and then run on 12v battery supply which is likely to be weaker and variable the pump cannot reach the set pressure.Result pump keeps running as pressure switch cannot operate at set cutoff pressure.

Talk of the 'sweet spot' reminds me of several vans where I've managed to find it and all has been well for months at a time on either form of power and then, for no apparent reason they seem to slip out of synch. You then get a couple of days faffing about seeking the 'spot' again and the process repeats several weeks later.

Kdc wrote:

petermcd wrote:Although a pressure switch would depend upon voltage defeats me .... should it not just switch according to water pressure ?

The pressure switch operates on pressure,the voltage and consequently the current will determine the pumps ability to produce the pressure. in turn this means if set whilst on EHU and its derived 12v supply which will be strong and steady and then run on 12v battery supply which is likely to be weaker and variable the pump cannot reach the set pressure.Result pump keeps running as pressure switch cannot operate at set cutoff pressure.

do the Shurflo/Flojet not also have (built in?) pressure switches? if so, why do they not need adjusting when moving from ehu to 12v and back again?

Diaphragm and not rorary impeller,I believe you will find diaphragm pumps are more powerful and efficient and the pressure is monitored internally behind diaphragm and mushroom non return valves which achieve/sees pressure build up quicker than rotary and external switch with non return which is remote from the pump and senses whole water system. I know you will say the system is pressured behind shurflo ,it is ...but efficiency makes the difference.

Have not solved problem yet BUT whilst rooting around in the exceptionally ‘busy’ area under the Starboard bunk I found the duct from the heater to the outlets was disconnected. Pushed it back into place and lots of lovely warm air now.

petermcd wrote:I adjusted our water pump to operate correctly when the van is connected to EHU (ie volts = 13.8v), BUT it  then misbehaves (ie does not switch off) when not on EHU (ie volts = 12.6V).

Have you tried setting it to operate correctly when not on EHU?
I am thinking that setting will also work for when on EHU.

I have never adjusted my pressure switch and it's OK for both EHU and non EHU.

Don, in short, yes I have. Actually tried setting it for non EHU and then for EHU but whichever I do it’s no good for the other. It’s quite tedious getting under there and adjusting ... but ...I am now quite adept. Shall be spending 3 days later this year ‘off EHU’ at FolkEast and would really like it to be OK for then ...
Peter M

I second autosleepyDon’s method,it’s the way I’ve set mine and it’s very rare I have to reset or tweek it.

The switch is a pressure switch, nothing else. Pressure low = switch on, pressure high = switch off.

If you adjust it so it can turn off the switch off on the battery (circa 12 - 12.6v) then it must also turn off on EHU (circa 13.8v) The only difference should be it will turn off faster on EHU because the impellor can spin faster.


What actually happens on EHU and on battery?

HairyF .... when switch adjusted correctly on EHU than pump operates normally, however when EHU removed then pump runs steadily and does not stop.

When switch adjusted to operate correctly on battery (without EHU) it cycles on/off when EHU is on.

I did find some instructions ‘on line’ for the Whale system (eventually) and it describes those symptoms .... vaguely suggests a surge damper (whatever that is) may help.

It does confirm that system operation does depend upon the voltage.


Peter M

‘Then’ not ‘than’

OK that helps

When the pump is in "high speed" mode it can quickly raise the pressure to the switching level in the region of the switch such that it turns off. There are then two possible scenarios.

The rest of the system i.e. pipes, water heater are still not up to pressure so it dissipates into those area until the pressure drops and it turns on again. 

This would be made worse if a] there is a constriction limiting the flow beyond the switch or b] there is air somewhere such as the heater which is being slowly compressed working a little bit like an accumulator (or possibly a bit of both). However eventually the cycling should stop once everywhere is up to pressure

If it continues to cycle then pressure is being lost somewhere but this should happen off EHU as well. Unlike a piston and valve pump like the Shureflo an impellor pump must have a dedicated non return valve because the pressure in the pipes would leak back through the pump when it is not running. These can leak at high pressure but not at low.

I don't know your layout but it would be better if the switch is after the tap off to the heater and not close to the pump to prevent pump surge activating it.

petermcd wrote:I adjusted our water pump to operate correctly when the van is connected to EHU (ie volts = 13.8v), BUT it  then misbehaves (ie does not switch off) when not on EHU (ie volts = 12.6V).
I wonder if anyone has fitted a ‘voltage regulator’ in the pump supply so the voltage at the pump is constant ? A quick ebay search shows many v.regs or dc-dc converters at quite modest cost.
Peter M

Hi Peter, I fitted a Lithium leisure battery which reduces the gap between the voltage on ehu and voltage off ehu. I don't have a problem with the pump pressure setting but I have heard it can be a constant problem. My solution is rather expensive and might then cause other issues so I would suggest you try a dc to dc regulator. If you get one with a nominal 12V output and an input range of up to 18V and minimum of 10A rating I'm sure it will fix the problem.