Surging Pressure Washer

[Rick Hughes]

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.

[MuddyMike]

different

Probably a blockage on the inlet side.

Mike

[Roger Mills]

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?]

[Ret.]

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

[Rick Hughes]

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.

[Rick Hughes]

Changed lance to scrubber unit ... still the same, so not related to hose or lance.

[Steve Walker]

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

[The Medway Handyman]

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.

[The Medway Handyman]

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.

[The Medway Handyman]

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.

[Rick Hughes]

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.

[Rick Hughes]

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.

[The Medway Handyman]

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;

pressure needs increasing 'very slightly'. Or a new valve.

p.s. Not using Hozelock 'Waterstop' connectors by any chance?

[Old Codger]

I have a Karcher and the motor keeps running. OK, it is quite old - cylinder rather than upright.

[Rick Hughes]

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.

[Roger Mills]

OK, how about this for a theory . .

He says that water flows through ok at mains pressure with the pump not running, so there isn't a conventional blockage in the pipework. He says that two different nozzles behave the same, so it's unlikely that they're *both* blocked.

I reckon that the lining of the pressure hose is de-laminating, and cutting off the flow. Then the by-pass opens and releases the pressure, the pressure hose recovers for a bit and lets through another pulse - and then the whole thing repeats on a once per 4 second cycle.

Got to be something like that!

[Rick Hughes]

OK ... the pressure hose is in s**t order, outer covering all peeling off, so inner could be crap. It was going to be changed this year.

I don't have a spare hose to try though ... so that limits my next step

[The Medway Handyman]

Could well be Roger. Although I would expect the delaminating hose would has caused a blockage in the nozzle.

My current money is on the by pass valve.

[The Medway Handyman]

That would make it pretty old. They may well have used the same design unloader/by pass on the newer models though.

[John Rumm]

What happens if you disconnect the pressure hose and let water squire out the output spout - does it still surge?