My Dad has a Karcher pressure washer - K550M, it's few years old now,
it's recently developed a fault.

Symptoms are that when turned on (with the water connected and turned
on), the pump 'pulses' on and off - with cycle time of say about 4
seconds - instead of staying turned off until you squeeze on the
trigger. It will sometimes pump water ok once the trigger is pulled,
sometimes it cycles on off. - I've fiddle about using a different jet
etc. Though that shouldn't make any difference anyway to the main
problem

I'm guessing it's something to do with the pressure/flow sensor (or
whatever it has) on the pump. Anyone know if there is anything I can
fiddle with before I have look at it.


--
Chris French

chris French wrote:
My Dad has a Karcher pressure washer - K550M, it's few years old now,
it's recently developed a fault.

Symptoms are that when turned on (with the water connected and turned
on), the pump 'pulses' on and off - with cycle time of say about 4
seconds - instead of staying turned off until you squeeze on the
trigger. It will sometimes pump water ok once the trigger is pulled,
sometimes it cycles on off. - I've fiddle about using a different jet
etc. Though that shouldn't make any difference anyway to the main
problem

I'm guessing it's something to do with the pressure/flow sensor (or
whatever it has) on the pump. Anyone know if there is anything I can
fiddle with before I have look at it.

Try the washer without the gun attached and see if it does it.

--
Sir Benjamin Middlethwaite

chris French wrote:

My Dad has a Karcher pressure washer - K550M, it's few years old now,
it's recently developed a fault.

Symptoms are that when turned on (with the water connected and turned
on), the pump 'pulses' on and off - with cycle time of say about 4
seconds - instead of staying turned off until you squeeze on the
trigger. It will sometimes pump water ok once the trigger is pulled,
sometimes it cycles on off. - I've fiddle about using a different jet
etc. Though that shouldn't make any difference anyway to the main problem

I'm guessing it's something to do with the pressure/flow sensor (or
whatever it has) on the pump. Anyone know if there is anything I can
fiddle with before I have look at it.

Mine went through a spate of cycling like that, but only when you pulled
the trigger - it was down to a small part-blockage somewhere and
completely cured by cleaning. Not sure if that might help put you on
the right track?

David

chris French wrote:
My Dad has a Karcher pressure washer - K550M, it's few years old now,
it's recently developed a fault.

Symptoms are that when turned on (with the water connected and turned
on), the pump 'pulses' on and off - with cycle time of say about 4
seconds - instead of staying turned off until you squeeze on the
trigger.

Two possible causes, if on suction rather than mains tap pressure it could
be air getting sucked in. Check hose, clips etc.

It will sometimes pump water ok once the trigger is pulled,
sometimes it cycles on off. - I've fiddled about using a different jet
etc. Though that shouldn't make any difference anyway to the main
problem

I'm guessing it's something to do with the pressure/flow sensor (or
whatever it has) on the pump. Anyone know if there is anything I can
fiddle with before I have look at it.

Sounds like the by pass valve may have gone out of kilter. When it was new,
what happened when the trigger was shut. Did the electric motor continue to
run or did it switch off?


--
Dave
The Medway Handyman
www.medwayhandyman.co.uk
01634 717930
07850 597257

On Tue, 12 Sep 2006 13:02:54 +0100, chris French wrote:

My Dad has a Karcher pressure washer - K550M, it's few years old now,
it's recently developed a fault.

Symptoms are that when turned on (with the water connected and turned
on), the pump 'pulses' on and off - with cycle time of say about 4
seconds - instead of staying turned off until you squeeze on the
trigger. It will sometimes pump water ok once the trigger is pulled,
sometimes it cycles on off. - I've fiddle about using a different jet
etc. Though that shouldn't make any difference anyway to the main
problem

I'm guessing it's something to do with the pressure/flow sensor (or
whatever it has) on the pump. Anyone know if there is anything I can
fiddle with before I have look at it.

I've had this two or three times with my rather ancient Kew pressure
washer[1]. Usually a small bit of grit or similar inside the pressure
lance, which after bit of fiddling and cursing about trying to rinse the
lance out from the nozzle end seems to clear itself. I did once get
problems with using a stop connector onto the hose coupling on the washer.
The pump was actually sucking water out of the hose and intermittently
closing the stop connector. I changed the connector for an ordinary one and
the problem was immediately solved.

[1] Bought, at a guess, about 25-30 years ago at a 'Special Show Price' at
the Ideal Home exhibition. When I pick it up now, I find myself wondering
how on earth I managed to lug it back on the train. :-)


--
the dot wanderer at tesco dot net

In message , The Medway
Handyman writes
chris French wrote:
My Dad has a Karcher pressure washer - K550M, it's few years old now,
it's recently developed a fault.

Symptoms are that when turned on (with the water connected and turned
on), the pump 'pulses' on and off - with cycle time of say about 4
seconds - instead of staying turned off until you squeeze on the
trigger.

Two possible causes, if on suction rather than mains tap pressure it could
be air getting sucked in. Check hose, clips etc.

Nope on mains pressure. My washer (also Karcher) works fine there.

It will sometimes pump water ok once the trigger is pulled,
sometimes it cycles on off. - I've fiddled about using a different jet
etc. Though that shouldn't make any difference anyway to the main
problem

I'm guessing it's something to do with the pressure/flow sensor (or
whatever it has) on the pump. Anyone know if there is anything I can
fiddle with before I have look at it.

Sounds like the by pass valve may have gone out of kilter. When it was new,
what happened when the trigger was shut. Did the electric motor continue to
run or did it switch off?

The motor turns off when the trigger is shut- or rather did.

Thanks everyone for their comments, In reply to points others have
raised.

Note- this problem is occurring without actually using the lance or
anything. Just turn on water, turn on washer, instead of it just sitting
there quietly until you squeeze the trigger it does this pump on/off
cycling thing all the time.

It's not blockage in lance, I've had that problem before which is only
obvious when you try to use the washer.

It's not low water flow - I have that problem at home sometimes (crap
flow from my garden tap) - but that again is only evident when using the
washer, sometimes it will stop for couple of seconds when using the
lance.

Yes, I've swopped the lance/trigger unit for one from my own washer,
same problem.

I'm certain it's inside the unit itself, I was just hoping someone might
be able to say - ah yes, it's x, or give me some idea what to look for
before I delve inside
--
Chris French

chris French wrote:

Note- this problem is occurring without actually using the lance or
anything. Just turn on water, turn on washer, instead of it just
sitting there quietly until you squeeze the trigger it does this pump
on/off cycling thing all the time.
SNIP
I'm certain it's inside the unit itself, I was just hoping someone
might be able to say - ah yes, it's x, or give me some idea what to
look for before I delve inside

Its a non return valve on the shut off system.

When the machine is in use operating at say 100 bar and the trigger is shut,
the rise in pressure opens a valve and allows the water to flow to a
pressure switch. This switch will then 'break' to turn the motor off.
There will be a non return valve which is designed to keep the switch under
pressure so the motor remains off.

When you pull the trigger again the pressure on the switch drops so the
pressure switch will 'make' and turn the motor back on.

Whats happening is that the non return valve is leaking slightly, so the
pressure on the switch drops a little, allowing the switch to 'make'. The
motor starts and the pressure rises 'breaking' the switch so it stops. It
will continue to cycle like this.

Never had a K550M apart, but there are some good parts diagrams on line with
Karcher spares agents. Google for Karcher Spare Parts.

Take the pump head off (loads of little bits!) and you should find inlet &
outlet valves. The non return will be somewhere between the outlet valves
and the outlet of the machine. It might even be accessible from the outlet
itself. It will be near an electric cable that operates the contactor when
the pressure switch operates. Probably a dodgy O ring.

HTH


--
Dave
The Medway Handyman
www.medwayhandyman.co.uk
01634 717930
07850 597257

"The Wanderer" wrote in message
...
On Tue, 12 Sep 2006 13:02:54 +0100, chris French wrote:

My Dad has a Karcher pressure washer - K550M, it's few years old now,
it's recently developed a fault.

Symptoms are that when turned on (with the water connected and turned
on), the pump 'pulses' on and off - with cycle time of say about 4
seconds - instead of staying turned off until you squeeze on the
trigger. It will sometimes pump water ok once the trigger is pulled,
sometimes it cycles on off. - I've fiddle about using a different jet
etc. Though that shouldn't make any difference anyway to the main
problem

I'm guessing it's something to do with the pressure/flow sensor (or
whatever it has) on the pump. Anyone know if there is anything I can
fiddle with before I have look at it.

I've had this two or three times with my rather ancient Kew pressure
washer[1]. Usually a small bit of grit or similar inside the pressure
lance, which after bit of fiddling and cursing about trying to rinse the
lance out from the nozzle end seems to clear itself. I did once get
problems with using a stop connector onto the hose coupling on the washer.
The pump was actually sucking water out of the hose and intermittently
closing the stop connector. I changed the connector for an ordinary one
and
the problem was immediately solved.

[1] Bought, at a guess, about 25-30 years ago at a 'Special Show Price' at
the Ideal Home exhibition. When I pick it up now, I find myself wondering
how on earth I managed to lug it back on the train. :-)


--
the dot wanderer at tesco dot net

I had identical symptoms on mine (K300) when there was a slight leak on the
discharge connector "O" ring. It was more of a seepage than a leak and was
caused by a split "O" ring. I haven't actually tried it as yet but I'm as
sure as can be that was the problem.

If there is no external leak on the high pressure side then there could be
one internally (pool of water under washer when in use?). The other
alternative could be that the non-return valve(s) between the pumping head
and the discharge could be allowing water to pass back to the low pressure
side internally i.e. it has to be this if there are no external leaks.

Best of luck.

In message , The
Medway Handyman writes
chris French wrote:

Note- this problem is occurring without actually using the lance or
anything. Just turn on water, turn on washer, instead of it just
sitting there quietly until you squeeze the trigger it does this pump
on/off cycling thing all the time.
SNIP
I'm certain it's inside the unit itself, I was just hoping someone
might be able to say - ah yes, it's x, or give me some idea what to
look for before I delve inside

Its a non return valve on the shut off system.


snip

Thanks, for the suggestions from you and sam, I'll report back once i've
had a chance to look at it.
--
Chris French