Diaphragm water pumps?

[Derek Uzzell]

Here's a simple enough question...

 

When a diaphragm water-pump (eg. a SHURflo pump) is not running, water cannot pass back through it in an outlet-to-inlet direction - ie, the pump then functions as a non-return valve. Obviously water can move through the pump inlet-to-outlet when the pump is running, but does anyone know whether water (or air) can pass inlet-to-outlet when the pump is stopped? Basically, if you picked up a disconnected SHURflo pump and blew hard into its INLET, would the air pass through the pump?

[trooper]

It will on all the diaphragm pumps I have worked on.

[Clive]

It should not and the Whale one I have on the shelf here does not.

 

Just think about it, if water could pass backwards through the pump when it was stopped the pressure would instantly fall and the pressure switch would instantly turn the pump back on again. It would "hunt" rapidly. We all know that when a water pump keeps turning on by itself to pressurise the system without any taps being turned on means its either a leak somewhere or the valves in the pump are cream crackered.

Simples

 

C.

 

[dipsticks]

In my experience of Sureflo and Flojet pumps (and most others) air/water may pass from inlet to outlet when the the pump is not running but not from outlet to inlet. However air/water will flow easier (inlet to outlet) when the pump is running.

 

I think this is important to consider if you, as I do, want to use air pressure to evacuate water from the pump and pipework to prevent freezing during the winter/lay up.

 

I have fitted a tee piece adjacent to the pump in the inlet pipe with a stop valve behind it on the tank side. In the tee is a car tyre valve. To drain and evacuate the water from the pump and pipework I shut the stop valve, open all the taps in van, switch on the pump then pressurise the valve with compressed air to blow all the water out of the pump and system. It works a treat.

 

Don't forget to drain the water heater and empty the tank, and of course open the stop valve at the start of next season.

[Rayjsj]

Derek,

Sorry to 'Butt in' on your post, I am away at present in the van over Christmas/New Year and have (I think ?) a problem with my Pump, It keeps 'cycling' about every 5-10 minutes, I have checked ALL connections inside the van, and there are no leaks ?? ( Clive's post seems to point to the valves being 'cream crackered' ?)

I have a Calorfier cylinder which has an Electric Immersion heater, could the water/pressure be evaporating ? causing the pump to 'cycle' ? just a thought., it must have an 'overpressure valve' somewhere in the system.

Took quite a time to check every connection, which are 'jubilee clip' type. Van is Autocruise Starlet II (starburst) 2005 with an Eberspacher heater/ water heater. Any Ideas or 'possible's' would be welcome. thanks. Ray

[Melvin]

Derek Uzzell - 2011-12-27 10:06 AM

 

Here's a simple enough question...

 

When a diaphragm water-pump (eg. a SHURflo pump) is not running, water cannot pass back through it in an outlet-to-inlet direction - ie, the pump then functions as a non-return valve. Obviously water can move through the pump inlet-to-outlet when the pump is running, but does anyone know whether water (or air) can pass inlet-to-outlet when the pump is stopped? Basically, if you picked up a disconnected SHURflo pump and blew hard into its INLET, would the air pass through the pump?

 

Hi Derek,

 

I have a spare Shurflo pump in my garage, I will go into my garage in the morning a carryout the blow test and let you know.

[Brambles]

I concur with Trooper.

[Derek Uzzell]

Thanks for the replies.

 

I had been looking at the website

 

http://www.keepfloeing.com/about.html

 

for the Floë product that involves a similar principle to that described by dipsticks.

 

I have a gizmo that I bodged up from a 15mm brass plumbing compression fitting and a truck tyre-valve. I unscrew the shower head from the motorhome's shower hose and screw the gizmo into the end of the hose. Using a 12V tyre-pump I can then pressurise via the tyre-valve my Hobby's water system 'downstream' of the SHURflo pump. Subsequently, by opening the taps, residual water can be purged from the system. Because a SHURflo pump (when not running) acts as a non-return valve preventing water from passing in the outlet-to-inlet direction 'my' method of purging residual water does not require an additional stop-valve.

 

However, although my gizmo method works reasonably well (and cost nothing and needed no modifications to the motorhome's water system) it is very apparent that it would be better and more efficient to use the sort of arrangement shown in dipsticks's photo provided that pressurised air would pass through the pump in the inlet-to-outlet direction. (It needs to be said that the Floë website recommends the same arrangement as dipsticks', but I wasn't confident that it would work properly.)

[Derek Uzzell]

Rayjsj - 2011-12-27 4:48 PM

 

Derek,

Sorry to 'Butt in' on your post, I am away at present in the van over Christmas/New Year and have (I think ?) a problem with my Pump, It keeps 'cycling' about every 5-10 minutes, I have checked ALL connections inside the van, and there are no leaks ?? ( Clive's post seems to point to the valves being 'cream crackered' ?)

I have a Calorfier cylinder which has an Electric Immersion heater, could the water/pressure be evaporating ? causing the pump to 'cycle' ? just a thought., it must have an 'overpressure valve' somewhere in the system.

Took quite a time to check every connection, which are 'jubilee clip' type. Van is Autocruise Starlet II (starburst) 2005 with an Eberspacher heater/ water heater. Any Ideas or 'possible's' would be welcome. thanks. Ray

 

This is a link to a SHURflo manual:

 

http://www.shurflo.com/files/RV-Installation-Manuals/Classic-Series-Pumps/Premium%20Plus%20Pump%20-%20911-352_L_2088-453-144%20_444_.pdf

 

SHURflo suggest that the following checks be carried out:-

 

-----------------------------------------------------------------------------------------------------------------------

 

PROBLEM - RAPID CYCLING:

 

Check for restrictive plumbing and flow restrictions in faucets/shower heads.

Check that any water filter/purifier is on a separate feed line.

 

PROBLEM - PUMP WILL NOT SHUT-OFF / RUNS WHEN FAUCET IS CLOSED:

 

Check the output side (pressure) plumbing for leaks, and inspect for leaky valves or toilet.

Check for air trapped in outlet side (water heater) or pump head.

Check for correct voltage to pump (±10%).

Check for loose drive assembly or pump head screws.

Check that the pump-valves are not held open by debris or the rubber swollen

Check pressure-switch operation.

 

OPERATION & SHUT-OFF ADJUSTMENT

 

Pump cycling may be caused by excessive back pressure created by one or more of the following within a plumbing system:

 

? Low flow from partially open faucet.

? Water filters not on separate feed lines.

? Clogged water filters.

? Restrictive elbows, shut -off and check valves.

? Use as few elbows and valves as possible in the first two feet [.6M] after the pump.

? Flow restrictors in faucets and shower heads.

? Long lengths of small I.D. lines.

? Pipe/tubing should be at least 1/2" [13mm] I.D. for main lines.

? Restrictive fittings and connections (elbows, "T's", feeder lines to faucets, etc.)

 

To minimize cycling, consider removing plumbing restrictions or simply install a SHURflo accumulator after the pump. Cycling should be minimized to prevent pulsating flow, and to achieve maximum pump life.

 

If the pump is cycling rapidly increase the setting by turning the screw clockwise (11/2 turn MAX.) until the pump operates for 1 sec. with at least 2 sec. "OFF time".

 

-----------------------------------------------------------------------------------------------------------------------

 

If you can't find any evidence of a leak (and small leaks can be a beggar to find) then I suggest you try screwing in the pump's pressure-adjustment screw a bit to see if that does any good. (Even if your pump is not a SHURflo, it's likely to have some means of adjusting the pressure-switch's sensitivity.)

 

See also

 

http://www.outandaboutlive.co.uk/forums/forums/thread-view.asp?tid=25936&posts=28

 

 

 

 

[dipsticks]

I would be reluctant to apply any pressure to the delivery side of a pump especially were it not running and especially with compressed air (it expands) into a 'closed' system prior to opening the taps.

 

My method described, I open the taps prior to applying the flow of air, uses the flow of 'generally' un-restricted air directly through the pump and all the plumbing to eject the remaining water in the direction of normal flow. It has worked well for me anyway.

 

Good luck

 

DS

[Derek Uzzell]

dipsticks - 2011-12-27 11:18 PM

 

I would be reluctant to apply any pressure to the delivery side of a pump especially were it not running and especially with compressed air (it expands) into a 'closed' system prior to opening the taps.

 

My method described, I open the taps prior to applying the flow of air, uses the flow of 'generally' un-restricted air directly through the pump and all the plumbing to eject the remaining water in the direction of normal flow. It has worked well for me anyway.

 

Good luck

 

DS

 

There's no particular problem pressurising the water system on the 'delivery' side of the pump (ie. the part of the motorhome's water system that begins at the pump's outlet and ends at the 'taps') with air as long as one takes a modicum of care.

 

The average diaphragm water pump will pressurise the water system to at least 15psi (my Hobby's SHURflo pressurises to 20psi), so pressurising to 15psi - which is what Floë advise - shouldn't cause any harm. It is, however, vital when pressurising the 'closed' system to monitor the rising pressure accurately as employing a very powerful tyre-pump, garage-compressor, or using an inaccurate pressure gauge, could lead to over-pressurisation damage.

 

The Floë purging technique differs from yours as, after pressurising the closed system to around 15psi with all water outlets closed, pressurising is stopped and just one of the motorhome's outlets is then opened. This causes the pressurised air in the system to be expelled strongly through the now-open outlet, forcing any residual water from the water-hose leading to that outlet. That outlet is then closed, the system repressurised, and the process repeated with another outlet., etc. etc.

 

With my shower-hose lash-up I find that I need to use the Floë procedure (pressurising the closed system to 15psi before opening an outlet) to cause water to be expelled effectively from the outlets. I've experimented with running the tyre-pump continuously while all the outlets were open, but air pressure just disappeared through any outlet-hose that already had no residual water in it. I've also tried running the tyre-pump continuously with just one outlet open, but that failed to produce the degree of water expulsion that could be obtained using the Floë procedure. Essentially, my tyre-pump (an RAC-700) is unable to produce/maintain sufficient air-pressure within an 'open' water-system to force residual water effectively through already-open water outlets.

 

In your previous posting you say that you "pressurise the valve with compressed air to blow all the water out of the pump and system". May I ask what you use to provide the compressed air, please?

[Brambles]

I am just thinking you might be better to use a hand of foot pump suitable for inflating air beds, lilos and the like which will have much bigger air flow at low pressure than a high pressure tyre pump.

 

I just stick a short hose and rubber connector over a tap and blow the air backwards out of the drain pipe using man powered lungs, and then run the pump which seems to blow enough water out of the pump and pipes to not be a probem freezing.

[Melvin]

Derek Uzzell - 2011-12-27 10:06 AM

 

Here's a simple enough question...

 

When a diaphragm water-pump (eg. a SHURflo pump) is not running, water cannot pass back through it in an outlet-to-inlet direction - ie, the pump then functions as a non-return valve. Obviously water can move through the pump inlet-to-outlet when the pump is running, but does anyone know whether water (or air) can pass inlet-to-outlet when the pump is stopped? Basically, if you picked up a disconnected SHURflo pump and blew hard into its INLET, would the air pass through the pump?

 

Hi Derek,

 

As promised I have tried your test on the Shurflo pump, you answer is NO it cannot

[trooper]

You will find its a matter of how much wind you have, >:-(

[graham]

We had the same cycling every 5 minutes occurence a couple of years ago. It started very suddenly and we could find no leaks anywhere. Then I realised it had started when I put something under the seat where the little yellow dump valve was sited. I checked and all looked ok but a packet of loo roll was just resting on the lever. Moved it off and all was fine. You can open the valve by pushing it down and it must have just cracked it open. When we got home I made up a little cover to stop it happening again.

[Derek Uzzell]

trooper - 2011-12-28 4:33 PM

 

You will find its a matter of how much wind you have, >:-(

 

I wondered if that might be so...

 

As dipsticks' arrangement pressurises air in the water hose 'upstream' of the SHURflo water pump (ie. on the pump's inlet side) and the similar arrangement recommended by Floë does the same, then logically it must be possible for air to traverse the pump inlet-to-outlet, but quite possibly for this to happen greater pressure is needed than a human's lungs can provide.

 

The above arrangement requires a shut-off valve to be installed in the water hose between the T-piece/tyre-valve through which the air will be pumped and the motorhome's fresh-water tank. As I know that my SHURflo pump won't let air pass outlet-to-inlet when the pump is stopped, and I'm comfortable pressurising the water system to 15psi, I'd prefer to put the T-piece/tyre-valve immediately 'downstream' of the water pump (ie. right next to the pump's outlet) and thus dispense with the need for a shut-off valve. However, locating the T-piece/tyre-valve there would be difficult in my Hobby's case.

 

The Hobby's water system uses reiinforced flexible hose and a mixture of jubilee-clips and X-FIX 'manifolds' as shown on the following webpage:

 

http://www.comet-pumpen.de/en/products-rv/water-supply-system/x-fix.html

 

Having had one of the X-FIX fittings come apart last winter (presumably pushed apart by water freezing within the fitting) I really want to expel as much residual water from the system as I can. Sending a blast of pressurised air up each hose that feeds to a water outlet seems like the right way to go and, as long as air will pass satisfactorily through the water pump inlet-to-outlet, dipsticks' arrangement would be best (and easiest to install) for the Hobby.

 

There's a Floë-related article on page 190 of MMM November 2011 and (although the MMM piece deals with a motorhome with a submersible pump) I'd install the shut-off valve and T-piece/tyre-valve as shown in the MMM article - that is in the water hose close to where it emerges from the fresh-water tank. I'd prefer not to have to run the pump while pressurising the system, but, if a non-operating diaphragm pump significantly inhibits the air-flow (as dipsticks suggests), I'd just have to accept that the pump would need to be running during the pressurisation phase.

 

 

 

 

 

[trooper]

Years ago I made up a way of pressurising, gently a system, Get an old bicycle tube, cut of about 4ft,

To include the valve, seal one end and connect the other end to whatever you want to lightly pressurise,

Pump it up and you are away.

Worked well on old series 1 land rover braking system, but would work on anything.

[Derek Uzzell]

trooper - 2011-12-28 7:14 PM

 

Years ago I made up a way of pressurising, gently a system, Get an old bicycle tube, cut of about 4ft,

To include the valve, seal one end and connect the other end to whatever you want to lightly pressurise,

Pump it up and you are away.

Worked well on old series 1 land rover braking system, but would work on anything.

 

Can't see how that wheeze could be used in this case - or at least not effectively.

 

If I wanted to pressurise the Hobby's water system with air in the simplest manner, I'd just disconnect the water-supply hose that attaches to the fitting on the top of the fresh-water tank and stick a modified tyre-valve in the hose's end (much as dipsticks has done with a T-piece fitting). But where would the technical challenge be in that? ;-)

[Brambles]

"But where would the technical challenge be in that?"

 

Derek, perhaps putting in a new water tank after you have split it with the air pressure!! ;-)

[Derek Uzzell]

Brambles - 2011-12-29 9:27 AM

 

"But where would the technical challenge be in that?"

 

Derek, perhaps putting in a new water tank after you have split it with the air pressure!! ;-)

 

"...I'd just disconnect the water-supply hose that attaches to the fitting on the top of the fresh-water tank and stick a modified tyre-valve in the hose's end..."

 

Why would you think pumping air through the tyre-valve fixed in the end of the water-hose that's now not connected to the fresh-water tank would have any effect on the tank itself?

 

(Even if I were attacked by sudden demetia while doing this and pumped air into the fresh-water tank, instead of into the hose leading to the water pump, it shouldn't cause harm as the tank is well vented.)

[Brambles]

Ahhh! Ok, never read properly, I assumed you meant the inlet to tank.. was not thinking properly influenced by thought of an inflating tank and desperate need to think of a technical challenge.

Oh Hum! shall go back to sleep still suffering the effects of an over indulgent Christmas.

[trooper]

My way, the tube acts as a reservoir to hold air at a controlled pressure, a compressor will give a very high pressure, with the risk of damage unless a regulator is fitted.

It works on brake systems so it would work on small water systems.

[Derek Uzzell]

trooper - 2011-12-29 12:37 PM

 

My way, the tube acts as a reservoir to hold air at a controlled pressure, a compressor will give a very high pressure, with the risk of damage unless a regulator is fitted.

It works on brake systems so it would work on small water systems.

 

My experience is that, to successfully expel residual water in a motorhome's water system will demand either a continuous flow of relatively high-pressure air passing through the hoses (which I believe is what dipsticks' 'all taps open' technique involves) or a short sharp blast of air down each hose caused by pressurising the complete 'closed' system to a safe level (15psi or so) and then opening a tap (which is the Floë methodology and the effect produced by my shower-hose gizmo). Using a pressure of just a few psi won't provide sufficient 'push' to clear residual water from more complex water systems like my Hobby's.

 

It's said that there's nothing new under the sun, and I vaguely remember (50 years ago?) something similar to your bicycle inner-tube idea being suggested to force lubricating oil through motorbike clutch and brake cables. I've got a feeling there was even a commercially available product that used that principle for Bowden-cable lubrication.

 

It's also interesting how close conceptually dipsticks' arrangement of a shut-off valve and T-piece is to the Floë product now being marketed. Presumably another instance of parallel development.

[rolyk]

Derek Uzzell - 2011-12-30 9:18 AM

 

It's also interesting how close conceptually dipsticks' arrangement of a shut-off valve and T-piece is to the Floë product now being marketed. Presumably another instance of parallel development.

 

This is just the kind of remark that deters people from posting on this forum.

 

To put the record straight, dipsticks made up the tee piece last year and was kind enough to also make me one. So, if Floe have since produced a similar product it is purely coincidental. The inference that dipsticks has simply copied the Floe product is uncalled for.

 

Roly

[Derek Uzzell]

rolyk - 2011-12-30 12:44 PM

 

Derek Uzzell - 2011-12-30 9:18 AM

 

It's also interesting how close conceptually dipsticks' arrangement of a shut-off valve and T-piece is to the Floë product now being marketed. Presumably another instance of parallel development.

 

This is just the kind of remark that deters people from posting on this forum.

 

To put the record straight, dipsticks made up the tee piece last year and was kind enough to also make me one. So, if Floe have since produced a similar product it is purely coincidental. The inference that dipsticks has simply copied the Floe product is uncalled for.

 

Roly

 

Roly

 

As you've been an O&AL forum member for over 3 years, I'd like to think that you will have read enough of my forum entries to appreciate that I'm not inclined to snipe at other members in the manner in which you've accused me.

 

My observation that it was "interesting how close conceptually dipsticks' arrangement of a shut-off valve and T-piece is to the Floë product now being marketed" was in no way intended to infer that dipticks had copied the Floë product.

 

I had concluded from dipsticks' postings that he had come up with his brainchild some while ago (ie. before the Floë product had begun to be marketed) and I had assumed that Floë had developed their product completely independently with no knowledge of dipsticks' idea. Consequently, my comment "Presumably another instance of parallel development" was meant to be taken at face value and not as any sort of underhand slur on dipsticks.

 

I'm sorry that you considered my remarks to be offensive; they were never intended to be interpreted as such.