I have a 5hp electric pressure washer that uses a CAT 3DX pump.
The pressure has been falling off and now is at a point that it is
The input filter is clean, I took the unloader apart and things look
OK in there.
I am now left with the pump itself I think. I pulled it apart (the 8
allens and the 3 caps). The pistons look OK, looking in the holes, I
don't see anything obvious with the check valves, no broken springs,
no contamination. I can see all the way through all the passages and
they are open.
I think I am down to ordering a rebuild kit but by the time I get a
seal kit ($90) and a check valve kit ($164) I am 85% into the price
of a hole new pump assembly with everything attached.
This is a $700 pressure washer, the pump is $300 and the kits are $254
At this point I am about to start pumping WD40 or some other solvent
through it to see if that doesn't free something up. I don't see I
have much to lose since tossing the pump is the next step.
I would really enjoy hearing something better since I have another CAT
4 piston pump on the shelf that is bad the same way and a little
electric pressure washer that doesn't work that well either.
I am no expert but i have rebuilt many of those style piston pump
heads for a spray car wash business.
Similar symptoms as you describe. The sprayers would go from great to
suddenly loosing pressure. After another week of use the sprayer
would be practically useless.
90% of the time a rebuild of the pump head would fix it. Some times
the metal check valves at the top of the piston would be the culprit
other time the cups or seals in the piston itself would be the
problem. Eventually we would just rebuilt the whole top. Most times
there would appear to be nothing obviously worn on the parts so even
the smallest amount of wear must cause the trouble. I did notice over
time that the metal check valve cups would appear polished where the
new ones had a dull faced flat finish.
If your sprayer is well used then it could very well be the piston or
check valve assembly.
If it has been accidentally run dry on occasion that will speed up the
Occasionally, when our stock of pump rebuild parts was depleted i
experimented with trying to refinish the metal check valve cups and
their seats by honing or lapping with various fine finish files ,
stones and emery cloth to get a pump working again for a while. I
would essentially take the metal cup and hone or lapp against a known
flat surface and try to get the finish to the similar satin finish the
new ones would have. Doing this made it obvious that the polished wear
rings were actually uneven , and deeper than apparent to the naked
eye. I suppose if the valve turns a bit the uneven wear will cause
them to tilt and zap the pressure.
anyways I hope this helps.
Thanks Robb. That is what I was believing myself. We have used this a
lot and our water really sucks. I am going to try the WD40 thing, just
to be sure it isn't just gummed up somewhere but I think a new pump is
how I am going to go. The parts are almost as much as a pump.
On Thu, 22 Sep 2011 14:48:40 -0400, email@example.com wrote:
OK I did the WD40 trick. I attached a hose to the intake and one to
the output, and cycled about a pint of WD40 through there until it got
up to about 110 degrees, (can getting hot in my hand, a minute or so).
I turned it off, hooked it up and I got 2600 pounds when the unloader
popped off and about 2100 with a 15 degree nozzle on it. I can live
One more thing WD40 can do for you.
I still think a pump is in my future but not right now.
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