Sunday, 18 September 2011


Has your Karcher Pressure Washer suddenly lost pressure?
Ever wondered how pressure washers work?

My K3.80 model lost pressure recently and it gave me a chance to find out just how pressure washers DO work - (something I've always wondered about but have never really found a clear answer to on the Web).
Unfortunately though, I spent well over £140.00 on a replacement Karcher pressure Washer before I decided to take the old one apart, (prior to despatching it to the local tip), just because I couldn't stand the thought of being without a pressure washer on hand.

but........ if I'd known that I could have repaired my old Karcher for as little as £6.74, I could have saved myself a lot of money. Grrrrrr.

After removing the wheels, various hoses and the front/outer 'housing' of the pressure washer, I found the business part of the washer nestling in the back/outer housing. Quite simply, this was a motor housing with what turned out to be the 'Pressurising' bit, bolted to the end.

This is the 'Business' end - THE PUMP

Looks big doesn't it, but its suprisingly small.
The threaded Outlet for the hose to the 'lance' can be seen on the top, and the Inlet from the garden hose is on the side.
Just behind the top 'Outlet' you can see the smaller clear plastic inlet where the cleaning liquid pipe attaches to the pump housing.
The entire Pump Housing is attached to the motor/gear housing by four bolts, (you can see two of the bolt holes in this picture).

Click on the pictures to enlarge.

And this is the underside of the Pump Housing.
You can see that there are 3 'Chambers'.
These are just like the cylinders in a car engine, and there are 3 'pistons' in the motor/gear housing, (to which this is attached), that move up and down in these cylinders.
At the top of each cylinder there are inlet and outlet valves......... again, just like a car engine.

And this is my rather poor attempt at a diagram to show how the Pump works -
(Click on the diagram to enlarge)

 One BIG TIP here...... if you DO decide to remove the Pump Housing from the motor/gearbox, make sure that when you undo the four bolts, (that secure the Pump Housing to the motor/gearbox), keep the entire assembly UPRIGHT because the gearbox is full of 'black' light oil which will go everywhere if you tip the gearbox over.

Now for the crunch....... WHY DID MY KARCHER LOSE PRESSURE?

There are a number of reasons why pressure washers lose their pressure, like insufficient water pressure from the garden hose, a blocked filter where the garden hose connects to the pressure washer, etc. but if you've checked all these things and the motor's racing, (not cutting out like normal) but you are still only getting a trickle of water out of the lance, then it's probably something more serious in the pump........ just like mine.

So, take a look into the cylinder chambers of my own sick pump........ (This part of the pump can be simply pulled away from the rest of the Pump Housing) 

In the bottom two cylinders you can see the white 'heads' of the inlet valves, but in the top cylinder, the inlet valve has pretty well disintegrated.                                                  
This was interesting, because during the few weeks prior to the washer totally losing pressure, the spray lance occasionally became blocked with what looked like very tiny bits of congealed cleaning liquid/soap, but I now realise that these tiny bits of white 'soap' were, in fact, bits of the inlet valve that had broken off.

 Now let's look at the cylinder and valve assembly a bit closer;

Above - This is looking at the cylinder and valve assembly from the other side. The three Inlet valves have little red 'caps' that can be prised off to remove the valve & spring. The Outlet valves are in the middle and are held in place by the small assembly that I have pulled out and shown in the right of this picture.

 And here are 2 Inlet valves, the 'shattered' valve at the top clearly shows the damage. The second valve is intact. You can now see just how small these valves are when compared to the pound coin. They're only little bits of plastic, but they get a darned good hammering when the pump's running, so it's hardly suprising that they eventually give up the ghost.

With this shattered Inlet Valve in place, the pump was just forcing the water back into the garden hose rather than through the outlet valves to the lance. Sucking the water in and blowing it back where it came from was what it amounted to!!

Luckily, I managed to find a set of 'replacement' valves on the exceptionally good Espares website - - listed as Karcher Pressure Washer Moulded Part Kit  all for just £6.74 incl VAT & postage !! (Aug 2011), and they arrived 2 days later, took about 5 minutes to fit, and after another 15-20 mins of re-assembling the entire pressure washer and connecting it to power and water, Bingo! a perfectly functioning Pressure Washer again.

I'm now the proud owner of TWO Karcher Pressure Washers....... but I didn't need to be.

If you start to experience occasional 'blockages', in the lance, that appear to be very small bits of white plastic, it could be an indication that pump valve problems are looming.
And if your Karcher eventually loses all pressure, but the motor is still running, (even though you've checked supply water pressure and filters), then I would suspect the cylinder valve(s).

Don't just throw the washer away - open it up and have a look - after all, what have you got to lose?

You never know, you too might be able to repair your washer for a little over £6.00.