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low pressure on pressure washer

15 years ago

Hi. I've read through all the related posts trying to find an answer but have not found one that addresses my particular problem. I have a Karcher K3.99M electric pressure washer that worked well but has slowly lost pressure. I did all the suggested troubleshooting steps but nothing has worked. I am wondering if the pump heads on these inexpensive units ($80 at Home Despot) can just wear out. I have taken the unit apart down to the pump itself, and can verify that the three push rods are fine. It appears that the way this pump works is that the push rods push water through three ports each of which has a small spring loaded plastic plunger (which I think may act as a check valve to keep water from moving backwards). When I turned the motor shaft by hand I could see that air was moving through these ports, so I am assuming the pump is fine. But when I connect it all up and run it, it produces pressure, but not much. The inlet water flow is OK, and I checked the inlet filter, so its not that. Here's a clue though - I tried a working unit next to it (not a Karcher, but another brand with the same pressure specs). Without the power on and without the wand attached, when I turn on the hose, I get a substantial flow through the working unit. When I do the same with the problem unit (the Karcher) I get very little flow. Maybe this is because there is a difference in pump design, but maybe this indicates a constriction inside the pump. If anyone out there has a Karcher unit like mine, can you do me a favor and run the same test and tell me how much water you get through the unit under the same circumstances (i.e. without the power on and without the wand attached, but the hose attached and turned on). I know the answer will depend on the water pressure at the hose (mine is 60 lb.) but I just need to know whether you get a good flow or a very limited flow. This will help me diagnose my problem. I realize that this is an inexpensive unit and I could just go buy another one, but I would at least like to try to fix it if possible. Thanks! By the way, it's not the wand, since the wand works fine on the other unit.

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Comments (2)

boltonranger
15 years ago
Have you checked the inlet screen on the pump?
Basic I know; but that could do it.
-br
ranger_ric
Original Author
15 years ago
That was the first thing I checked. Clean as a whistle.

Here's another question. This is not mine, it's a friend's, and upon further discussion with him it turns out that he has been using this pressure washer in a rather unconventional way. He has been using the wand to clean algae from the bottom of his pool, by taking the wand underwater and putting the nozzle right on the plaster. The nozzle was set at highest pressure setting while he was doing this. I wonder if there is anything about this scenario that could explain the low pressure problem.

Thanks.
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