KB9030 pressure washer, looking for cause of problem. pulsing when on standby and I think a drop in pressure when in full operation. Regards Bill

There are full strip down videos in this link

https://www.google.com/search?q=karcher+KB9030+strip+down

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It sounds like you either have a clogged nozzle or one that is too small for your pump. At lower speeds the pump is pumping less gpm. So your unloader valve does not cycle. Then when you go to full power. The engine is running faster and pumping more gallons per minute. The nozzle is too small or clogged and so the bypass opens and closes ( surges) Try a new nozzle that is the right size for your machine.

you have changed a part or you have a blockage in the inlet valve

you may have restriction or clogged nozzle causing pressure buildup in trigger

If you have a Karcher then you should always post your machines barcode.

full article on nozzles :
http://repairshed.blogspot.com/2013/09/pressure-washer-lance-nozzles-what-you.html

The spill valve operates at approx 20% higher than specified pressure washer operating pressure. If you have any lance issues then the pressure could be running higher than specified (machine running at same pressure as spill valve operation pressure)

your machine produces a fixed flowrate of water (maybe 8 litres per minute) and your nozzle is a fixed size. the diameter of the nozzle determines the back pressure. A piece of debris could further close your nozzle orifice and increase the back pressure. Using a new lance that has the wrong nozzle fitted can also cause this issue.

The karcher barcode is on a silver sticker and is usually 15 digits long. Example 156987400000123 is actually model 1.569-874.0 and serial number 00123....

sounds like your unit has a bypass problem either needs adjustment or replaced

I assume you have run some water through the supply hose before connecting it up, they don't like pumping air. The most likely problem is a blockage at the inline filter where the supply hose enters the unit. If there is no filter there then the problem may be more serious. Grit may have entered the pump and worn out the pistons and then you may as well buy a new one because it won't be worth repairing.

This fault is within the control head, under the detergent valve is a small spring loaded valve that acts to induce the detergent, this will have failed, the shaft of the component breaks off the disk base leaving a small hole in the centre of the disk. This is enough to allow pressure past the component. The machine will pulse when operated and will not induce the detergent. I've looked everywhere to find this part as I have a karcher with the same fault.

Check the oil. This is what happens when it is low on oil with my pressure washer. Kind of a safety feature.

Hi, I had the same problem, Replaced the O rings and the rubber seals and cups inside the pressure washer and eventually the hose itself burst. Turns out the hose was leaking, internally between the inner sheath and the outside plastic cover, for quite some time and this caused the pulse. New hose and pressure cleaner is as good as new.