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Shurflo question

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NickT
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Post by R88BUC Mon Apr 29, 2024 8:33 am

Having had continual airlocks with the submersible pump in my Bourton I decided to fit a 20psi Shurflo pump. Consulting many of the post on here it was a relatively easy fit and all seemed well. During my first trip away I found that a short flush of the loo or opening a tap for a short time caused the Shurflo to make a humming noise but not pump. This noise would go on continuously until a tap was opened fully then the Shurflo would pump properly but seemed louder than normal. If a tap is opened to wash or fill the sink for example the pump works fine with normal noise level. I think a small pressure drop (short flush) causes the pressure switch to trigger but the remaining pressure in the system prevents the pump from running (stalled). The pump is new but I wonder if it is faulty? The set up is not usable in this state and I’m planning to go back to the submersible if I can’t find a solution. 🤞

Regarding the submersible pump I found a post on here where someone found that by increasing the length of pipe the submersible pump is on so the pump rests on the bottom of the tank at 45 degrees eliminated the air locks. What’s the thoughts on this? is it worth dropping the tank to try this?
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Post by NickT Mon Apr 29, 2024 7:07 pm

Hi R88
Sounds to me like the pump is "cycling", so the pressure switch adjustment screw in the base of the pump needs to be screwed in (maximum of 1.5 turns, according to Shurflo instructions).
If that doesn't cure it an accumulator may be needed.

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Post by Dave 418 Mon Apr 29, 2024 9:00 pm

When I helped to fit a Sureflow pump it was advised that an accumulator should be fitted with it. Other people have said it saves the pump tripping on for short use of the water like flushing.
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Post by The Bargee Mon Apr 29, 2024 10:15 pm

Stalled might just be the word. Does this happen with the battery on charge? A steady electrical humming or buzzing noise would suggest that the motor is struggling to start the pump, which could indeed be a faulty pump but might possibly be due to insufficient volts at the pump.

Is there an external non-return valve in the system? If so where is it, before or after the pump?

As I have said elsewhere in my opinion a lot of the wiring in these vans is undersize, causing excessive voltage drop. Shurflos need a good jolt to start since the swash plates are under some degree of back pressure from the system, unlike the in-tank submersibles which are just a freely rotating centrifugal impeller. If the pressure doesn’t drop promptly as an outlet is opened then the motor might be constrained by the back pressure in the system. Measure the voltage at the pump as somebody else tries to flush the loo. If the voltage dives the pump is drawing power but cannot start.
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Post by Caraman Tue Apr 30, 2024 7:42 am

The Bargee wrote:...
Is there an external non-return valve in the system? If so where is it, before or after the pump?

...
If there is, the Shurflo hasn't been installed correctly.  The Whale NRV that is integrated with the Whale pressure switch should have been removed when the Shurflo was fitted.  But even if it remains connected to the Shurflo's water inflow, it shouldn't stop the pump from working.  Some installations have a second Truma NRV that should stop water from the hot water tank mixing with the cold water but again this should have no impact on the pump.

The OP reported trouble when a tap is only partially open i.e. it is restricting the flow.  We tend not to do this as it makes the pump go on and off quickly just as the Whale used to.  So for us its taps fully open or shut.

Some have suggested fitting an accumulator.  We haven't done this and haven't found the need to but maybe if we did it would make the pump cycle on and off more slowly when a tap is only partially open.

The OP reports a hum but no water flow from the pump so I expect the normal cycling of the pump on and off when a tap is only partially open is not the problem.
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Post by R88BUC Tue Apr 30, 2024 8:17 am

Thank you all for the suggestions. To keep the installation simple and the space available in this version of Bourton, the pump was sited upright and basically replaced the whale pressure switch. The Shurflo pressure adjustment screw is not accessible with the pump in location and therefore I couldn’t easily make adjustment. The stalling issue is not mentioned in the reasons or troubleshooting sections of the manual for making adjustments so I didn’t try while I was away.
Last night I removed pump and decrease the adjustment screw in stages. After a few steps the stalling issue has been eliminated, so I can only conclude that as mentioned above back pressure was preventing the pump starting I guess the stalled motor would eventually have burnt out if left.
It would not be very easy to fit an accumulator without major plumbing changes.
I don’t think there is an external Nrv.
The main issue now is the vibrating noise of the swing wall makes as the system pressures back up.
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Post by The Bargee Tue Apr 30, 2024 8:27 am

The reason that I mentioned the NRV is that some installers, including myself, fitted an external NRV just downstream of the pump (on the outlet) to overcome the problem of tiny particles in the water fouling the built-in NRV and allowing back flow to the tank. If that (optional) NRV is installed upstream (before) the pump then the system pressure is lying against the swash plates. You wouldn’t think that this would cause a problem but going back some time (seventies) I recall a lot of problems with failed micro switches (the actual pressure switch) where the micro switch would fail “on” and the pump would run until it physically stalled and burnt out (or the fuse blew). Hence again some installers (including myself) also fitted an external pressure switch to improve reliability.

Personally I don’t think the NRV hypothesis is the problem, but it is a possibility if one has been fitted inadvertently, or remains 8n place, upstream of the pump.

The OP perhaps needs to address again the question of is this reported “hum” indeed continuous as he says, which would suggest a stalled motor, or intermittent in the sense of “on-off-on-off” which would be “cycling.”

I would still suspect voltage drop but it is easy to test this either by meter or by simply connecting the pump temporarily to the battery with some heavier cable.

Anyway, I now see that the OP has apparently cured the problem by reducing the cut-off pressure, which will effectively de-rate the pump and reduce the starting load on the pump motor, so all would seem well!
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Post by Caraman Tue Apr 30, 2024 12:17 pm


The main issue now is the vibrating noise of the swing wall makes as the system pressures back up.
Try removing the access panel on the swing wall marking which is the top which makes it easier to replace.  Then fit foam pipe insulation to the hot and cold water pipes.  This helps reduce the throbbing noise in the bathroom.  Outside the bathroom we found the Shurflo to be quieter than the rather whiny Whale.  However I think this depends on how the Shurflo has been mounted i.e. it’s feet aren’t screwed too tightly or the water pipes are not too short and pressed against the internal fittings.
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Post by R88BUC Tue Apr 30, 2024 12:50 pm

Thanks Caraman, I will try that, as you say the pump it’s self is not too bad.
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Post by grahamsb Sun May 05, 2024 11:40 am

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I also have a Shurflo pump fitted to our Bourton, after the original pump failed.

The pump is fitted on large rubber mounts which cut down the noise. I also have some sound deadening material around it.

I haven't found the need for an accumulator, although I was prepared to fit one.

The pump runs smoothly, even if the taps are only partially opened. I do, however, have aerator/spray attachments (see photo) fitted to both taps, which restrict the flow. While they reduce the amount of water used by half, they still produce a strong spray, which can be directed around the sink and wash basin. With such a small water tank fitted to the later Bourtons, the water saving is a godsend. I have also reduced the water used in the shower by half, with an aerating shower head.
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