Cat pump problem

I have a Cat Pumps Pressure Washer Pump — 4 GPM, 4000 PSI, Model# 66DX40GG1 powered by a Honda GX390 engine. It works well of I run it off a garden hose, that is supplied with water under pressure. However if I run it off a gravity feed tank it does not run to full pressure (only about 1500 psi). I had the water in the tank well above the inlet of the pump. I had a reputable shop open it and they said all is well. The inlet hose has large diameter. A couple of local service people have told me that the problem is with the pump design, it is high speed pump and is not designed to run off a tank but only water under pressure. Is there any truth to this?

A 66DX40G1 should pull from a tank pretty well. (Your number has 2 G’s in it?) Direct drives as a rule don’t pull from a tank very easily, but that particular pump should do pretty well. How many hours are on your pump? Inlet seals could be worn. What size and type of supply line are you running from your tank? Maybe post a pic or two? Feel free to give me a call. I’ve done what you’re doing and it’s totally doable with that pump, just gotta get it just right for it to work well and not damage your pump.

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Email may be less expensive. I’m not sure what the phone rates are from Auckland to Greenville.

Oops! Thanks, Tim.

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For some unknown reason the problem has gone away. Thanks heaps for you help.