Which petrol Pressure Washer?

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Choosing a Petrol Pressure Washer.

If youre considering purchasing a petrol driven pressure washer, you've probably already used an electric machine in the past, and realised you need more power or greater independence from a power source.

Petrol Engines

Most petrol engined power washers will give you just that. Engine sizes vary from 6.5 Hp, 7, 9, 13 & 14 HP units. They are usually 4 stroke engines which means, they need oil in the engine sump. Usually they are coupled directly to the high pressure pump, though some can have a reduction gearbox in between.

A Reduction gearbox is usually found on the more powerful models where the intended use is for long hours and heavy duty work. The other benefit of a reduction gearbox is that the pump runs at a much slower rpm (1400 rpm) meaning that it is easier for the pump to suck water from a standing source ( water tank)  - so theres no need for a mains supply.

Pump Types. axial pump  petrol washer crank pump

Industrial Pumps are normally made from Brass, and are of two types... the Axial design ( on smaller machines) and the popular crank pump, featuring 3 pistons that are normally fitted to heavier duty machines.

The power of the pressure washer pump is determined by the operating pressure and the amount of water it can pump. Pressure is measured in either Bar or PSI (pound per square inch) with one Bar equal to 14.5 psi. Water flow is measured in L/m (litres per minute). The combination of the pressure & flow rate is what gives you the cleaning power. One is no good without the other.


For general cleaning around the home, or for cleaning cars, bikes & garden machinery; a 6.5 or 7 HP model will be sufficient - giving pressures of 2800 - 3000 psi @ around 12 litres per minute.

For Industrial cleaning jobs... as the saying goes .. " the bigger the better". So 9, 13 or 14 Hp engined units will give the best performance; up to 3500psi @ 15 litres per minute. At these pressures - they'll shift heavy dirt & debri from agricultural plant, boats, HGV's & industrial equipment. Their most popular use would be for Professional Driveway Cleaning; where the pressure washer will be used for up to 8 hours a day, giving reliable, powerful performance.

The other benefit of greater performance is the fact that any accessories you connect to the petrol pressure washer - such as a drain cleaner, turbo nozzle or rotary cleaner - will work far better on a more powerful machine. This means you'll get the job done a lot quicker too.