There are three main classes of petrol or diesel pressure washers:
1. Hobby – usually petrol driven, up to 5hp and use a vertical crankshaft engine, like a lawnmower, and have a small wobble plate pump hung underneath the engine. Like your lawnmower these are designed to be used occasionally for short periods of time. They won’t suck their own water either.
2. Budget priced – look the same as professional equipment but all the corners have been cut. You can identify this type of pressure washer, as it will have no reduction gearbox between the pump and engine. Reduction gearboxes are expensive but allow the pump to turn much slower. This means that the pump is not designed to suck its own water. It may do when new for a few months but it is primarily designed to be fed from a hosepipe. Check with your water supplier to see if this is permitted. (Most do not)
3. Industrial – what you need if you earn a living from pressure washing, or use pressure washers for long periods of time. Characterised by having a reduction gearbox which allows good suction and top of the range engines, designed to last, with quality filters and fittings.
The Demon petrol range can be viewed at:
http://www.demon-pressure-washers.co.uk/acatalog/Petrol_and_Diesel__Pressure_Washers.html