In article ,
Hugo Nebula writes:
Reading car forums, the overwhelming opinion is that a pressure washer
is needed to wash one's car properly. So I went and bought a cheap

Really?
I thought a problem with them for this purpose is the pressure
can take the paint off.

I do use one for washing the car, but the main purpose is to
pump the water from the water butt. I never point a high pressure
jet straight at the paintwork, or elsewhere where it might cause
damage. I use a soft brush attachment for washing, and a misting
spray for rinsing.

Halfords one, complete with snow foam attachment. The results were
disappointing to say the least.

I know it's not a mega powerful one, but I was amazed at how low the
pressure was out of the nozzle. I was certain my hose gave a more
powerful flow, so I did an experiment and timed how long it took to
fill a bucket, and therefore what the flow rate is from my tap. It
amounts to 1,000 litres per hour, nearly three times the flow rate of
the PW. Some of the best pressure washers only appear to give half of
that.

The flow rate from most is quite low.

Am I missing something here? Is pressure a function of the flow rate,

No.

To a first approximation, pressure x flow rate will be proportional
to the power consumption, but that ignores that some have efficient
induction motors, and others apparently have less efficient (and
probably shorter life) universal motors.

and if so, what's the point of a pressure washer if it gives less than
mains pressure?

They are much higher pressure than mains.

--
Andrew Gabriel
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