The Medway Handyman wrote:
Colin Wilson wrote:
Is it just me, or do they just throw the crap from the floor onto
your walls ? :-}

Like most tools there is a 'knack' to using them :-)

What actually happens is that the embedded dirt is removed from the
floor & dirty water hits the walls. Clean the floor, then wash down
the walls with lower pressure.

A more comprehensive answer to Colins question;

DIY pressure washers have flow rates that are very low compared to the
pressure. 100bar x 6 litres/min is common. An industrial machine at 100
bar would have a flow rate of 8 - 10 litres/min.

The balance between pressure & flow is important, high pressure/low flow
gives much more of an aerosol effect because the water droplets are very
small, resulting in a wet operator & muck all over the place.

The next consideration is the type of nozzle. If you had a simple drilled
hole in the nozzle you would get a straight 'pencil' jet of water maybe 3mm
in diameter. This would have very high mechanical efficiency, but would
take ages to clean any sort of area.

Most DIY machines & some lower end industrial have whats known as a 'vario'
nozzle which uses two metal plates to squeeze the pencil jet into a fan
shape. These can be adjusted to vary the shape of the jet between pencil &
fan by turning a ring on the nozzle that moves the plates. Vario nozzles
cause a large loss in efficiency and an increase in aerosol effect.

Next step up is to use a standard fan nozzle where the water stream is
forced through a slit into a fan shape. These are again not that efficient
and cause aerosol effect, though not as bad as vario nozzles.

The aerosol effect is caused by the very small size of the water droplets,
which easily become airbourne.

Better are the fairly recent Spectrum or Powerspeed type nozzles where the
inside of the nozzle is machined to spin the water stream into a fan. These
produce water droplets 4 times the size of a standard fan jet & greatly
reduce aerosol effect as well as improving cleaning efficiency - larger
droplets hit harder.

Best of all are 'Turbo' or 'Dirtblaster' nozzles. These use a mechanical
device to spin or oscillate a pencil jet into what appears to be a fan,
giving large area coverage, maximum mechanical advantage and much larger (10
times) water droplets than a fan jet. Hugely reduced aerosol effect, much
less splashback.

Floor cleaning tools like the Karcher Surf Cleaner have a rotating spray bar
inside a shroud and reduce splashback to almost zero.

HTH

Maybe I should add this to the pressure washer faq?


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