"Hugo Nebula" wrote in message
...
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
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.

Am I missing something here? Is pressure a function of the flow rate,
and if so, what's the point of a pressure washer if it gives less than
mains pressure?
--
Hugo Nebula
"If no-one on the internet wants a piece of this,
just how far from the pack have I strayed"?

Pressure washers are a positive displacement pump.
They deliver a fixed amount of water.
http://en.wikipedia.org/wiki/Positiv...acement_p ump

The pressure you get depends on how small the outlet orifice is.

So to get a higher pressure you adjust the outlet down.
If the outlet is wide open, you just get a miserable dribble.
(But it is the same volume of water.

There is a relief/bypass valve inside opens if over pressure ocurrs.
eg when the operating valve on the lance is closed.