Pressure boosting pump cycles when dishwasher fills

[lardconcepts]

I bought a Salamander Right Pump RGP80 to replace a pump in this old house of ours, which has ridiculous 15mm pipes all round. Without a pump, the toilets, washing machine, dishwasher etc all take 10 minutes to fill. With a pump, we get a wall-washing burst of water from the sink, but at least there's a hope of dispensing with that irksome floater (not in the sink, I hasten to add!).

The thing is, about a week after installing it, when the dishwasher filles the pump cycles on for half a second, then off for 1.5 seconds, and so this goes on for about 2 minutes until the dishwasher is full.

Putting my ear to the dishwasher, I can hear a gentle hum of a solonoid and also water still trickling in, so it's not the dishwasher cycling it. But, if I turn on the nearby kitchen cold tap for just a second, the pump stays on and the dishwasher fills in a more normal 20 seconds or so.

I phoned the Salamander helpline, and he said it was something to do with the surge of water being too much for the solonoid and "bouncing" it closed again. Does that make sense?

Anyway, he suggested a pressure vessel somewhere in the system to absorb the shock or surge of water. And yes, I've tried turning the service valve gradually closed. All that does is induce quite a loud "swooooosh, swooosh" as the surge rushes by the constriction.

Also, would that help my "turn the tap on, get a trickle for half a second, then a sudden trouser-splashing torrent" problem?

For that, the local plumbing centre suggested a gate valve closed off a bit, rather than a pressure reducer. But it's not the pressure that's the problem, it's that suddent gush when the pump kicks in.

So, before I go spending what looks like being =A330+ on a pressure vessel, is that going to help? Thanks!

[dennis]

I would have thought a pressure vessel and a non return valve would be better. Put the valve on the mains before the pump and the pressure vessel after the pump. You may need a flow switch to ensure the pump switches on as soon as the vessel starts to supply water or it will just provide high pressure for a second or three and then the pump will see some flow and you will get a surge. It depends on what the switch in the pump does when the tap turns on. If it detects the pressure drop soon enough you don't need another flow switch to detect the .

The pump may already have a non return valve too, so check the manual.

[Tim Downie]

15mm is normally perfectly adequate for toilets, washining machines, dishwashers etc.. Are you pumping from a storage tank, mains or a well?

It sounds to me like all your cold supply is coming from a storage tank. What's your mains supply pressure like? Is there any reason not to convert your cold supply throughout the house to mains fed rather than tank? Is your mains pressure to your tank very low?

Could it be that the dishwasher is fitted with a high pressure flow restrictor that's limiting the flow (and consequently the rate of pressure drop & pump triggering) in the pipework?

I'd be tempted to look at the inlet pipe for any such restrictor or perhaps a kink in the flexible pipe. You probably wouldn't want to completely remove such a restrictor but perhaps the restriction could be lessened somehow to allow freer flow.

Tim

[lardconcepts]

Yes, well spotted. A well is pumped up to a gravity feed tank in the loft. No way round it without spending =A31,000's on a pressurised bore hole, which isn't going to happen for very many years!

So, there's the core of the issue - it's pumping from a not-very-high header tank.

Thanks for all the other suggestions - no kinks in any pipes. Again, what I find odd is that turning the kitchen tap on for just half a second smooths the whole thing out and it runs properly.

I'm beginning to wonder if an air bubble is building up, with air somehow drawn in in the filter and UV unit? So, it goes: header tank > pump > tee off to first floor and tee to ground floor > UV unit > kitchen tap then dishwasher. Of course, the dishwasher doesn't need to be on the UV, but it's got a microfilter too which is a good thing to have.

[Jim K]

righto

does the dishwasher

[Jim K]

righto sounds like the flow is being interrupted or severly limted and your pump is cycling to and from (bouncing on) it's pressure switch.??

does the DW supply tap do this "trick" when DW is disconnected ? if so not dishwasher, but tap or pipe problem

if DW then options limited unless you fancy tinkering with DW or paying someone to tinker?

We have a whole house pumped supply run from a Draper pump with pressure vessel built in (=A3100 check on ebay) I believe that the pressure vessel apporach would alleviate your probs - both DW and the "kitchen sink flood" effect because the pressure vessel acts as a buffer between the FULL ON pump pressure and realistic usage patterns of household requirements.

I'd also consider putting your UV in front of all usage points - if someone were to draw a glass of water form your bathroom it appears they could be drinking non UV'd water from a storage tank?

Is the tank newish & properly sealed against dust, insects etc etc or old, open and "poxy"?

With a pumped system you could have a new tank anywhere (cellar, ground floor etc) and simply feed your cold system "backwards" (after capping off the storage tank supply of course!)

NB what's your HW like for pressure and flow - similar?

Cheers Jim K

[lardconcepts]

No, it's literally just when the dishwasher is filling on its own. The kitchen tap turned on momentarily cures it, and the tap on, on its own, doesn't do this.

I think I'm going to go with my gut feeling and the overall advice here and go for the pressure vessel idea.

Well, to be honest, we often run with the UV off anyway unless we have visitors. The only thing the UV does it make the water taste of plastic where the chamber gets hot.

The local authority test it every couple of years, and last time it passed, although it was borderline, but a few e-coli never hurt anyone! We drink mainly tea/coffee, and when we make cold drinks, it's usually squash/cordial mixed with cheapo 8p-for-2-litres supermarket fizzy water. We've never had a problem yet - we were drinking it with 3 dead field mice, before we noticed the lid had been moved, and never got sick.

Before anyone says it...I know, I know! And I know what being ill is like; I lost 2 stone in a week (and I only weighed 12.5 before) after getting Campylobacter from a Cantonese take-away.

But I appreciate the concern.

[John]

In such circumstamses the norm is a "pressure set" Ie a pump , pressure switch and a reservoir with a diphragm in it. This latter stops the pump from operating to often, the bigger the reservoir. (It's on the ressure side of the pump). The bigger the reservoir the better.

the flexible hose too elastic?

[John]

They're usually reinforced. (Like garden hose)

Yes - but some can still react a bit to shock waves so I guess there must be a bit of elasticity.

[lardconcepts]

OK, I'm going to go for it - are we of the opinion that bigger is better in the world of pressure (or expansion) vessels?

Here are 4, there's only =A310 between the 8 litre and the 25 litre.

- this is a link to a gigantic "compare these" screwfix URL, unless anyone else knows a better place/ has another suggestion?

Also, if it needs to be near a drain-off, it'll have to sit on a long- leg near the washing machine. Is it preferred to be as near as the pump as possible?

[Jim K]

to a point I suppose so yes

the draper all in one thing we have has a 24 litre vessel.

We can just about "small flush" a loo and wash hands before the pressure switch kicks in and fires up the pump.

Sooooo depending where your pump is (i.e. how intrusive the noise could be at 3am whilst recharging the vessel) - a bigger vessel (or two in parallel?) may be worthwhile to you.

I suppose there will be times when you will have to change the bladder/ diaphragm inside each vessel but in normal use there shouldn.t be any "leakages" or need to drain down - I've only done it once in a couple of years

Pass

Cheers Jim K

[lardconcepts]

Does it matter that the RGP80 uses a flow switch and not a pressure switch?

I realise these are questions I could ask the maker now I know where I'm going, so feel free to ignore it if this is getting tedious!

[Jim K]

ah with you - I'd guess yes it will, as I would expect it to only fire up when something moves *past* the flow switch, which will be long after the vessel(s) have pretty much emptied, if at all - as the vessels are pressurised with air on the *other* side of the bladder/ membrane there may be enough resistnece to your paltry flow rate to effectively knacker that solution:>).. ..mmm you could probly adapt it ? but a pumpset like ours for =A3100-150, Ebaying the salamander may be quicker and cheaper?

Cheers Jim K Cheers JimK

[<me9]

If it's on a drinking (potable) water supply it will need a WRAC approved one. The examples you gave are for central heating, a different kettle of fish.

[lardconcepts]

Oh good grief, just when I was about to order, now it gets complicated. I phoned up Salamander again just to give a final check that I was doing the right thing, and this time they said no, this pressure vessel idea wouldn't work, because it was low flow rate. They then suggested I bought this:

I bought a pump from them, they said my special half price offer was =A396 inc postage. The full price is =A3114. Not quite sure how they work out half price from that! Anyway, I declined.

He said it holds the pump at the right pressure so it doesn't turn on and off, but if the problem is flow rate (which they are now saying it is) then surely that wouldn't help? Also, he said it would stop the taps doing the "trickle then gush" thing, but I don't see how that could be.

For a punt with =A330 I can take the risk that a pressure vessel will work, but at =A396 I can live with a pump cycling on and off.

Any thoughts?

BTW, finally got through to the Hotpoint technical helpline - apparently, they have no technical knowledge about dishwashers, flow rates, solonoids etc, so they immediately launched into flogging me a

2 year supply of dishwasher cleaning granules for =A324. Sigh.

[Jim K]

well like I said ebay the salamander and buy a pumpset with vessel (ebay Draper or Clarke (machinemart) amongst others)

or

wild card:-

can you build a "dead leg" of 22mm say pipework that would be always full of air? so when your pump pressurises your cold water pipes it will also pressurise the air in the "dead leg" - then when a tap is opened the pressure of the air in the dead leg will push water at a reasonable rate out of the pipes until the flow switch on the pump "notices" and starts pumping - it would also probly help with the DW fill issues as the air would be working like a buffer (and like a small pressure vessel to reduce the pump cycles and allow the DW to fill at whatever speed it likes for longer than 1/2 a second ata time)

I hasten to add - I've never done this but maybe others can comment on the validity (or not) and what technical aspects (size, position etc would be required) - smaller dead legs are used for water hammer so it's not all *that*novel..

Cheers Jim K

[lardconcepts]

The problem is, I cocked up royally, thinking I was getting a good deal on the RGP80 at =A3170 instead of the =A3299 RRP. The next model up from mine goes for about =A370 on ebay, so I'd be instantly losing =A3100 on a 3 week old pump. So you can see my enthusiasm for finding a workaround!

Hmmm, that sounds interesting. Does anyone have any thoughts over that method rather than a pressure vessel? (eg, item 160376764781 on ebay)

[Jim K]

as only 3weeks can you not return it as "not fit for purpose" or do a deal somehow? did you pay by CCard?

mmm postman just been and so done a back of envelope calc and it would be a lot cheaper and a lot easier to buy that vessel than do dead leg of equivalent volume!!

Before you throw any more money at it it does seem you willl always have an "odd" setup with that pump -or more accurately *that pumps method of detecting when it is needed to be on*.

If you could change the flow switch (orr disconnect it) and install a pressure switch (or buy a vessel with one already on) to trigger the pump you will get to where you should be.

If you keep the flow switch and add a p vessel I expect you will have a mode like this:- open tap - reasonable flow for X seconds, flow and pressure drop till pressure in vessel is lower than in the bit of pipe between pump and pressure vessel, hopefully water then flows past pump's flow switch to vessel, detected by pump flow switch, pump kicks in and pressure & flow increase rapidly....so a peak; low trough; peak if plotted on a graph.

Your DW will probly appreciate that and the vessel absorbing some of the pumps "vigour", other activities at the sink etc may not be much better? I don't know...

A pressure switch OTOH would kick thepump in whenever the pressure in the vessel drops past it's (usually) adjustable trigger point - so the "lag" between water use and pump kicking in (the trough in the graph) would be shallower and I expect in effect the changes in pressure/flow not as noticeable.

Cheers Jim K

[Tim Downie]

I still think that you need to make absolutely sure that your dishwasher hasn't got a flow restrictor in the inlet.

A low inlet flow might not be enough to trigger the pump into action. Turning on the kitchen tap would trigger the pump, raise the pressure and

*now* with the higher pressure, the flow through the restrictor is high enough to keep the pump running.

Look for a washer with a small orifice in *either* end of the hose and have a look in the inlet in the back of the dishwasher to see if there's any sort of removable restrictor.

If you have one, you might not want to remove it completely but instead enlarge the hole or otherwise adjust it to be less restrictive.

Tim

[lardconcepts]

Tim. You da man, or whatever it is young people say. Here's the culprit:

restrictive filter, and then absolutely tiny holes. Check out the size of it in comparison to my grubby fingers. No wonder water isn't flowing much!

I looked at the connection end of the pipe before when you first suggested it, but could only see a filter. To look at the other end meant moving the whole worktop out, then the dishwasher, which I did because you seemed so insistant. Your insistance saved me about =A335 and half a day of buggering around. Very grateful - how come the experts on the phone didn't suggest this??

So, I guess it's there for a reason, probably to not flood the softener unit to quickly? What to do then - just drill out those four tiny holes into one larger hole?