Mr Fuxit wrote:
On 14 Apr, 21:43, "The Medway Handyman"
wrote:
Sparks wrote:
"The Medway Handyman" wrote in
dia.com...

Mark X wrote:
I notice that Makro are often selling petrol pressure washers
cheap.

Is it worth having a petrol version or should I just get an
electric Karcher from B&Q?

Pro's; Much more power usually available 5hp petrol machine = same
power as 3hp electric, most DIY machines are around 2hp max. Work
anywhere you can get water.

Cons; Cheap petrol engines can be trouble, IMO only worth looking
at Honda. Higher service cost. Noisier than electric, cost more to
run. Auto stop/start not possible so engine must be shut down
within minutes of closing trigger gun.

Really? - don't they just have a bypass valve in them, so water is
just pumped in a circle?
My old electric Karcher certainly does this!

By pass machines (electric or petrol) can only run in by pass mode
for a very short time. Each time the water goes through the pump,
through the by pass valve, back into the pump, through the by pass
etc it picks up a little heat from the friction of the pistons
through the seals.

The pump head on a pressure washer contains a very small amount of
water - an egg cup full approx. Doesn't take long for this to reach
a high temperature - which will soften the pump seals & allow water
to get past them into the oil in the crankcase. 5 mins on a cheap
pump, maybe 15 mins on a good one & your seals are buggered &
possibly the swash plate & bearings if the oil is contaminated
enough.

Thats why auto stop via a pressure switch is such a good idea. Not
perfect. Best solution, only found on industrial machines is a by
pass valve with a flow switch which detects flow through the by pass
& turns the motor off - sometimes via a timer.

--
Dave - The Medway Handymanwww.medwayhandyman.co.uk



My petrol (Briggs & Stratton 5HP) never gave me a moments trouble in 7
years of daily
using it commercially. Mind you, it was a "Cat" pump, not a bloody
awful swash plate pump.

"Cat - the pump with nine lives" as the advert used to say. One of the best
pressure pumps ever made. Old technology and all the better for it.

All the current manufacturers claim legion & manyfold benefits for swash
plate pumps, and they are slightly more effecient. The real reason they are
used is simply that they are very cheap to make. They by pass internally
through channels in the pump head giving the water no chance to cool down.

You could damage a Cat pump if you ran it in by pass for long enough, but
they usually by pass externally allowing the water to cool a bit.

They were often belt driven so they ran slower - another good idea. Most
modern electric machines are direct drive @ 2800 rpm. If your B&S machine
was direct drive it probably ran off the engines crankshaft via a reduction
box, modern machines tend to run off the camshaft in an effort to keep the
speed down.


--
Dave - The Medway Handyman
www.medwayhandyman.co.uk