Pressure washers / walls

[Colin Wilson]

Is it just me, or do they just throw the crap from the floor onto your walls ? :-}

[The Medway Handyman]

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.

[The Medway Handyman]

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?

[David]

So true, the one that we got with our Nilfisk is excellent, it makes a noise similar to a fan kind of thing.

[Colin Wilson]

I sense a worthy addition to the FAQ here !

Thanks for the reply :-)

[The Medway Handyman]

Welcome.

John Rumm. Could you add this bit to the FAQ for me/us please?

[John Rumm]

We seem to have two copies at the mo - one in the original FAQ, and another in the wiki... I have a feeling the faq one could just be replaced with a wiki link now.

OK, faq modified.

I have updated the "lance" section of the wiki article with the words from this thread. Feel free to adapt adopt improve etc.

if you want to edit the wiki, and don't already have an account then see:

(we had to knobble free for all account creation to kill off the spammers)