wrote in message
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On Sun, 2 Nov 2008 10:05:02 -0500, "MLD" wrote:


wrote in message
. ..
I understand that GPM can be as important or more important than PSI
for "getting work done". So, I'd like as high a GPM as possible,
obviously. I'd be using the pressure washer for occasional home use
and occasional semi-pro use for handyman/odd jobs.

But I'm concerned about source water flow. I'm on city water, but I
just checked an inside line and an outside hose, and I'm getting 4 GPM
max, maybe 3.5 GPM. Does that definitely rule out a 4 GPM machine?
I'm concerned about cavitation in the pump.

The chacteristics of a centrifugal pump (pressure washer) is pressure rise
(Delta P) vs Flow at constant speed.

A pressure washer is not a centrifugal pump. The ability to
create such high pressures can only be accomplished by a
positive displacement pump. All pressure washers that I am
aware of are piston pumps.

SNIP
In reflection, you're correct--the washers do have positive displacement
pumps. That being the case, as long as the downstream restriction doesn't
cause the pump relief valve to open the flow output should be very close to
pump spec. This is not to say, however, that centrifugal pumps are not
capable of generating high pressures.
MLD