Surging Pressure Washer

I have a KEW Hobby pressure washer ...... been great to date ... but yesterday started surging.
This is significant enough to make it useless, almost equal cadence between pressure & no pressure ... the outlet pressure gauge is also reading nothing ... but that may be just a duff gauge.
Anybody any experience with pressure washers ?
No shortage of incoming mains (pressure or flow rate) even tried different hoses & fittings to be 100% sure of that.
If I operate lance without unit being switched on ... water is jetting out OK. Plus when it 'surges' it does seem right pressure and flow at the peak of each surge.
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different
Probably a blockage on the inlet side.
Mike
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On 01/05/2011 15:50, Rick Hughes wrote:

At what rate is it surging - like several times per second, once every few seconds, etc.?
During this pressure fluctuation, is the motor running all the time - or does it keep starting and stopping?
When you fist turn it on with the outlet closed (i.e. trigger on lance not operated) does get up to pressure and then cut the motor, like it's supposed to?
[Anyone know how many pistons a typical pressure washer has in its pump, and what the rotational speed is likely to be?]
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Roger
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equal pressure / no pressure ... about 2 sec on 2 off or maybe a little less.

Motor running contiuously

Never done that ... iut would just run up to load and motor stay at load, never cut/in out. (Hobby 88 is model) sound wouldof course change, but does not stop running.
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On 01/05/2011 18:24, Rick Hughes wrote:

Hmmm, the ones i've used have all (okay all four different ones) cut the motor whenever there is no flow. Pull the trigger, the motor starts up, release the trigger, the motor stops.
SteveW
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On 01/05/2011 19:39, Steve Walker wrote:

The KEW Hobby was one of the first on the market, IIRC it had a bypass valve rather than a pressure switch which most modern machines use.
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Dave - The Medway Handyman www.medwayhandyman.co.uk

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That would tie in with the in-use sound ..you can hear pump getting up to pressure, and if you are 'jetting' it is one, sound, when you release the trigger, sound changes as I presume it reaches peak pressure and 'by pass' opens ... but certainly does not stop running.
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On 01/05/2011 19:39, Steve Walker wrote:

I have a Karcher and the motor keeps running. OK, it is quite old - cylinder rather than upright.
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On 01/05/2011 16:55, Roger Mills wrote:

Almost all have 3, they are generally axial swash plate pumps. Motor speed around 2800 rpm. Cheap ones have universal motors that run really fast.
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Rick Hughes wrote:

I had a similar problem with a Karcher - and prodding some grit out of the jet with the provided 'prodder' did the trick.
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Kev


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Changed lance to scrubber unit ... still the same, so not related to hose or lance.
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On 01/05/2011 18:25, Rick Hughes wrote:

Try it without the lance. Do you get a steady stream of water?

In that case it sounds like the by pass (or unloader) valve is out of kilter.
To explain whats occurring; Say the working pressure is 100 bar. The by pass valve is basically a piston held shut by a spring.
When the trigger is closed the back pressure rises to say 105 bar and forces the valve open - allowing water to flow back into the inlet & round in a continuous loop. When the gun is opened the pressure against the spring drops allowing the valve to close.
A partial blockage in the nozzle would cause the back pressure to rise & operate the valve, the pressure drops so the valve closes, the pressure rises & the valve opens, etc etc etc.
If the valve is out of kilter (or the spring has broken) - e.g. set too low - it causes exactly the symptoms you describe.
Page 5 part 60 here;
http://www.dolmar.nl/images/files/tekeningen/HP11.pdf
Spring pressure needs increasing 'very slightly'. Or a new valve.
p.s. Not using Hozelock 'Waterstop' connectors by any chance?
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Great explanation .,.. I am away for a few days with work ... will take a look, maybe a clean will fix :-) Don't suppose you have same parts list / drawings for the Hobby 88 ?
It is a rectangular box type, rather than upright.
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On 01/05/2011 20:55, Rick Hughes wrote:

That would make it pretty old. They may well have used the same design unloader/by pass on the newer models though.
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On Sun, 01 May 2011 20:47:52 +0100, The Medway Handyman wrote:

Just read through the thread, I still have a very old KEW Hobby, bought at the Ideal Homes Exhibition many many years ago. I also had this problem, and in the end it turned out to be using waterstop connectors on the inlet. Also had trouble with grit in the lance, had to buy a new lance, as the old one didn't lend itself to my style of DIY disassembly! :-)
Still in the garage unused now as it was bl**dy heavy to lug around, now replaced with a Nilfisk.
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On Thu, 5 May 2011 20:12:23 +0100, The Wanderer wrote:

I can't work out why waterstop connectors are supposed to be a problem or if they are how. When connected the male spigot physicaly pushes the valve open, no way can it be sucked shut.
Maybe some people put waterstops at both ends of the hose and the one at the tap end is sucked too far open blocking the flow? Easy cure for that...
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On Thu, 05 May 2011 22:26:23 +0100 (BST), Dave Liquorice wrote:

On the face of it, I've got to agree with you, there shouldn't be a problem. Except that from personal experience I can say there is! I can only think that the whole arrangement (the spigot, the rubber seal, the actual clearance when open) restricts the flow into the pump.
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Have to agree on that they are not flow related when connected, as you say they are physically open when connected, irrespective of water.
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On 01/05/2011 15:50, Rick Hughes wrote:

Only about 30 years worth :-)
Made my living selling them for years.

Penny to a pinch of poo its a partial blockage in the nozzle. Don't be too forceful in trying to clear it, nozzles are fairly delicate. Blow it backwards with an airline if you can.
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nope ... I took lance off and fitted a patio scrubbere - exactly the same surging, so not nozzle related. I also have a separate nozzle (rotating) tried that ... same surging.
Tech spec
80bar 1.3 hp nozzle pressure 88 bar most other specs are about hose size & dimensions etc.
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