Water pump question (1 Viewer)

[Camper634]

Could anyone please tell me if the water pumps fitted to modern Motorhomes (2017 Autotrail)have any sort of adjustment for water pressure?I have fitted a replacement cartridge filter in line with the cold tap in the kitchen,but even when I have the tap fully on the pump seems to cut in and out constantly.The previous filter didn’t cause this problem which seems strange.Thanks in advance for any suggestions.

 

[The Dudess]

Ours does this too (2017 Frankia), although only when running hot water. If the tap is turned to run cooler water then the pump runs continuously. I'm not sure either whether this is the way it's supposed to be or not.

 

[andy63]

The pumps are usually rated by the operating pressure...which one you have depends on the boiler you have fitted.. the most common is a 20psi pump..
Ill post a picture of the instructions for altering the cycle time of the pump if you have fitted a device that may restrict the flow...

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[andy63]

Ps.. i should have said that the adjustment screw is found on the pump head..

 

[Camper634]

This is the pump

 

[The Nomad]

There's no adjustment for the flow rate on such pumps, that is a fixed amount depending upon which pump you've got fitted , eg 7 litres per minute, 10 litres per minute, 12 litres per minute.

Many pumps do have a screw or Allen key adjuster on the end of the pump which alters the pressure on the rubber diaphragm inside and thus alters the point of pressure drop in the pipe leading from it at which the pump kicks in.

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[Musicboy]

Under the pump there is a screw which allows to adjust the flow .. If ya can get to it ( as shown in that diagram above ) then ya can adjust for an even flow ... Bit of a try but ya can prob get it near perfect .... good luck. Cheers

 

[Musicboy]

Ohh ... as above post / reply .... looks like it has an auto flow rate on that . Google Shurflo on yre model number to establish exact adjustments , if possible ...

 

[Musicboy]

Just an idea ...possible cause ... Yre pump is set up from factory to deal with the domestic use / flow of water . However the filter may be interup ting that flow & the pressure is building up back to the pump , resulting in the ad hoc performance .Just a thought ...Process of fault finding .... remove the filter & see what happens .?.

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[pappajohn]

The adjuster screw on pumps DOES NOT adjust the water pressure, it adjusts the point at which the pump stops.
The pressure remains constant at whatever the pump was designed to deliver.

 

[Diabalo]

Put an accumulator in line and that will help with the pulsing

 

[movan]

Deleted.

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[tonyidle]

The adjuster screw on pumps DOES NOT adjust the water pressure, it adjusts the point at which the pump stops.
The pressure remains constant at whatever the pump was designed to deliver.

It really does . It sets the system pressure at which the pump cuts out so the pump output never attains the maximum pressure it's capable of. It will also affect the flow rate if there's any restriction in the outlet pipework (there always is). An increase in pressure will force water to flow more quickly through the restriction.

 

[Blue Knight]

This has been a really informative thread but it doesn't seem to root cause the actual problem.

The OP has replaced one filter with a direct replacement (I suspect it's a genuine OEM type) so why is his system no longer working correctly.

I could be wrong here but surely the pressure is not going to fluctuate post filter swap unless there is a secondary problem with the system.

Any thoughts guys.

Edit: Was the filter a genuine OEM replacememt. If not then perhaps this is reducing the flow rate. (I'm just guessing now).

 

[motorhomer]

autosleepers have a pressure adjuster not on the pump itself but in the water supply pipe. It doesn't adjust the pump pressure but switches it on and off depending on pressure in the pipe. It may be that autotrails are the same. Its like I used to have in caravans years ago. If this is set incorrectly it can cause exactly the symptoms OP describes. It can need adjustment for voltage variation if on 12v. Its usually a white plastic thing with an adjuster on top.

Another thought. I would have thought it quite feasable that a new filter would have a different resistance to the old, which may have been partially clogged, and therefore slightly different water pressure as a result. Therefore needing to adjust the pressure switch as I have described seems quite likely to me.

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[Blue Knight]

autosleepers have a pressure adjuster not on the pump itself but in the water supply pipe. It doesn't adjust the pump pressure but switches it on and off depending on pressure in the pipe. It may be that autotrails are the same. Its like I used to have in caravans years ago. If this is set incorrectly it can cause exactly the symptoms OP describes. It can need adjustment for voltage variation if on 12v. Its usually a white plastic thing with an adjuster on top.

Another thought. I would have thought it quite feasable that a new filter would have a different resistance to the old, which may have been partially clogged, and therefore slightly different water pressure as a result. Therefore needing to adjust the pressure switch as I have described seems quite likely to me.

That's a fantastic bit of info

.........so the new filter is likely to be causing a slight imbalance to the pressure levels within the tube and the system is reacting accordingly.

That makes perfect sense.

 

[maxi77]

Sounds like a flow restriction in the new filter, pressure builds up, pump stops as water still can flow pressure drops, pumps starts again and guess what. First suggestin would be to replace the filter with plain hose and try again, if this removes the problem then the problem is the filter. Perhaps some debris inthe inket us us restricting flow or just this cartridge cannot take the flow.

 

[Blue Knight]

Sounds like a flow restriction in the new filter, pressure builds up, pump stops as water still can flow pressure drops, pumps starts again and guess what. First suggestin would be to replace the filter with plain hose and try again, if this removes the problem then the problem is the filter. Perhaps some debris inthe inket us us restricting flow or just this cartridge cannot take the flow.

That sounds like a great solution. I'm into modding cars (as a hobby) and I constantly battle against filter types, pressures, flow rates etc.

I've sometimes found that a so-called direct filter replacements have been significantly different in spec-terms to the original gear.

I think we're cooking on gas now

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[PeteH]

MOST of the (Shureflow) pumps fitted to `vans are rated 20psi, and 20 psi is what you will get on a good day!. MOST after-market filters have 3/8" connections which are likely to put a restriction in the system. IF the pump is "lazy" (old) this will show up more readily.

I have a similar system at home for "Drinking" water, and have experienced this effect with some "equivalent" filters, involving a significantly reduced flow, the supplier said he had changed his supply source and the replacement is significantly better.

 

[pappajohn]

It really does . It sets the system pressure at which the pump cuts out so the pump output never attains the maximum pressure it's capable of. It will also affect the flow rate if there's any restriction in the outlet pipework (there always is). An increase in pressure will force water to flow more quickly through the restriction.

When the tap is fully open the pump is at maximum pressure and cannot be increased.
Closing the tap increases water pressure to the point the pump switches off.....which will be below the pumps maximum pressure or the pump won't turn off.
So, the switch alters the static pressure, not the flow pressure.

 

[andy63]

When the tap is fully open the pump is at maximum pressure

John should that not read max flow ....not pressure...?

which will be below the pumps maximum pressure

The pressure the pump cuts out at will be the highest pressure the system will attain.. and that can be adjusted slightly by the screw on the pressure switch.. which can possibly alter how the pump cycles...
If it doesnt then as stated in the instructions i posted at the start an accumulator is most probably the best option.
Andy

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[pappajohn]

The switch operates on static pressure.
When the tap is turned off pressure builds in the pipework to the point the switch operates.
If it's a 20psi pump and the switch is adjusted to 18psi the pump will never attain 20psi as it's switched off at 18psi.
It could be adjusted to 20psi but can never exceed that, even if the switch is bypassed and the pump runs continuously, as that is the design pressure of the pump regulated by the size of the valve chambers and the stroke of the diaphragm.
If it were possible to increase pressure it would be easy to buy a (cheaper) 12psi pump and adjust it to any reasonable pressure with a turn of the screw.
As said, the screw alters the cut off point, at or below the pumps maximum pressure, not the actual pressure

 

[DaveandJen]

The in-line replacement filter cartridge is probably producing a restriction and causing the pump to run up to near maximum head (pressure) so it thinks all the taps in your motorhome are closed and turning off correctly and then restarting again when the pressure falls.

 

[tonyidle]

When the tap is fully open the pump is at maximum pressure and cannot be increased.
Closing the tap increases water pressure to the point the pump switches off.....which will be below the pumps maximum pressure or the pump won't turn off.
So, the switch alters the static pressure, not the flow pressure.

Sorry. I'm not being obtuse. When the tap is fully open the pump is at maximum flow and minimum pressure. Closing the tap increases water pressure to the point the pump switches off. The pump is switched off by the pressure switch which may or may not be part of the pump. The switch will have be set to a value lower than the pumps maximum pressure capability otherwise, as you say, the switch couldn't operate to turn the pump off.

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[pappajohn]

Sorry, thought I'd corrected that to flow which obviously I meant rather than pressure.

 

[tonyidle]

Sorry, thought I'd corrected that to flow which obviously I meant rather than pressure.

I did wonder.