wrote in message
...

So what are you disagreeing with?? Pump manufacturers don't want to run
their pumps under conditions that will result in cavitation-very bad, will
ruin a pump. In most cases they will specify the inlet conditions
(pressure
& temperature) under which they (pumps) should be operated. Specifying a
free flow supply is just a loose way of defining the pump inlet
requirements.

The manufacturer makes suggestion so that your pressure washer will
not be run in a way that may damage it. They want pressure at the
inlet. They know that their pressure washer isn't the only user of
your water supply. Showers, washing machines ect. will further reduce
the free flow rate.

Don't understand your comment-"when the relief valve is activated the
actual
flow at the inlet is reduced so that a less than adequate supply may
suddenly become adequate".

Example: If the pump can create 5GPM of flow and you have the
washer in rinse so that the relief valve is not activated then your
4GPM supply is not adequate for the rinsing stage. If the same 5GPM
pump is dumping most of the volume over the relief as it is when you
are power washing then you are only drawing about 1GPM from a 4GPM
supply so that during this power washing stage the supply suddenly
becomes adequate.

SNIP
You have a funny way of looking at things--Let me change your example around
just a bit. You have a free flow of 5 GPM and a pump that can put out 4
GPM. No problem it works just fine. Now increase the discharge resistance
such that the pump operates on its relief valve. The flow out of the pump
will drop to almost zero or slightly above zero.
In your example the pump will most certainly be in cavitation when not on
the relief valve, producing no flow, but when on the RV produces an output
of about 1 GPM. From your point of view, this suddenly qualifies as adequate
supply. I guess 1 GPM is better than nothing.
Why in cavitation--assuming a 50 psi supply pressure and a free flow of 4
GPM--- AT 5 GPM (pump demand) the inlet line pressure drop would be
approximately 75 psi (25% increase in flow requires 50% increase in pressure
drop). The pump will not work, it'll just screech itself to death.
I have a power washer, as you must also have, and it works just fine, so
obviously, my house supply more than meets the flow requirements of the
washer.
MLD