Buying a High Pressure Cleaner

Maybe you need a machine to clean cars, equipment or patio areas. You’ve either never used one or if you have maybe that rusting and dirt encrusted washer that’s given 10 years faithful service has just blown another fuse or the ‘bargain’ yellow plastic machine you bought from the DIY store has already stopped working after only 3 months use. Whatever the reason, if the time has come to purchase a new pressure washer here are a few tips on finding the most suitable machine for you.

Choosing a Pressure Washer

All the machines on the market have broadly the same design. They have a motor (electric, petrol or diesel), a 3-piston pump and a length of high-pressure hose with a gun and lance.

Hot or Cold?

The first question to ask is. Do I need a heated machine or will a cold only washer do?

A hot machine has what amounts to an oil fired central heating boiler under the cover in addition to the pump and motor. If you just clean the exteriors of vans, tractors or cars then a cold machine will be OK. You will however need to use some detergent to get a good, clean result. The jobs that a hot machine cleans best are where oil, grease or animal fat needs to be removed. This would included curtain sided vehicles, old engines and animal pens. The hot water will melt or soften the dirt and make its removal easier. Hot water will also make any detergent work better, giving a cleaner finish in a faster time whilst using fewer chemicals. The down side of having a heated machine are cost and weight. Compared with a cold machine of equivalent power and quality a hot machine will be about 3 times more expensive and 3 times heavier. It will also cost around 3 times more to service.

People often ask “what is the difference between a hot water machine and a steam cleaner?” A steam cleaner is a hot water machine that also has a water flow-reducing valve. When it is used, the amount of water going through the boiler is restricted, allowing it to heat the water to over 100 degrees centigrade. As it is under pressure whilst inside the boiler the water stays as a liquid. As it escapes through the jet at the end of the lance it immediately boils to steam. Steam is useful to remove very greasy deposits and for killing bacteria and other bugs.

EHRLE pressure washer


The second question is. How powerful does the pump need to be?

The power of a pressure washer pump is determined by the pressure it can produce 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 Lpm (litres per minute).

For most cleaning tasks a normal single phase, 230-volt electric machine is powerful enough. These can be plugged into a normal 3 pin electric socket. If however you have thick mud or muck to remove then a 3-phase 415-volt powered machine may be needed. If a three phase electric supply is not available consider a petrol or diesel engine machine.

karcher pressure washer

Understandably most people would look at the output pressure to judge the power of a machine. This does have a bearing on the ability of any given machine to clean, however the amount, or volume of water that the pump produces makes a greater difference to the cleaning effect. The easiest way to asses the power of a machine is to find the power consumption of the motor. This will give an accurate indication of the cleaning power of the unit. A single-phase 230-volt machine, one that runs off a normal 3-pin plug, will have a maximum electric motor power of 13 amps or 3kw. (If it had a more powerful motor this would blow the 13amp fuse in the plug) This equates to a pump output of 100-Bar pressure, or 1450 psi (pounds per square inch) combined with a water flow of 12 Lpm (litres per minute). This is the optimum pressure/water flow combination.

You will see single phase machines with a higher pressure than 100 Bar however if you look at the water flow this will be reduced. Examples are 130Bar with a water flow of 9 litres/minute or 140Bar at 8litres/minute. Neither of these machines will give a greater cleaning effect than 100bar/12Lpm.  Sometimes the water flow will be quoted in litres per hour (Lph) if this is the case then divide by 60 to find the litres/minute figure. Another thing to note is that some manufacturers will quote two water flows; the higher figure is water flow without the pump being under pressure. The lower figure will be water flow with the pump working at full pressure. Three phase or engine power will enable you to have a cleaner with up to 200 Bar (3000 psi) pressure and 21 litres of water per minute. This sort of power is enough to shift the thickest mud and the dirtiest machinery. Two hundred Bar is the maximum pressure used before specialist protective clothing needs to be worn.

Petrol, Diesel or Electric?

If you want more cleaning power, the choice is either an engine powered machine or a 415volt, 3-phase washer.  Electric machines are cheaper to purchase and service, however a 3-phase socket is not always available where the washer is needed. Petrol or diesel powered washers can be used in most areas but require more frequent servicing. Petrol engines are cheaper to purchase, easier to start and quieter when running. However diesel engines are more economical to run as they use cheaper fuel and less of it. Generally cleaning contractors and heavy plant yards use diesel machines whilst farmers and small businesses buy petrol-powered washers.

What type of pump?

The next question to ask is. How much work will the washer to do? This would normally be measured by the number of hours you expect the machine to run in a week. As a rule of thumb if you plan to use a machine more than 2 hours a week then get an industrial specification unit. The big difference between a domestic or light use commercial machine and an industrial or frequent use machine is the speed of the pump/motor unit. The cheaper machines have a motor that spins at 2800 revolutions per minute (Rpm). Heavier use machines have motors designed to run at 1400 Rpm. The slower running machines are under less stress and normally last at least four times as long as a fast running unit. In addition if your water supply is not great a slow running pump will suck water either out of a tank or water butt.

The better quality engine powered washers have a reduction gearbox between the output shaft of the engine and the pump to slow the speed of the pump down to 1400 Rpm.

With regard to the material that pumps are made out of, DIY machine pump heads are usually made from plastic, light duty washers are normally aluminium, whilst industrial pumps will have a brass pump head – a material that is strong and will not corrode.


It is always tempting to choose a machine with a low purchase price. However this is not necessarily the cheapest option in the long term. Domestic machines sold in DIY outlets are made to last for around 25 hours use – the amount that an average householder would use a machine over the course of 2 years. They are sealed units that normally have to be thrown away when they develop a fault as they usually cost more than the purchase price to repair.

As an example if you buy a cold water machine for £50 and it lasts for 25 hours this has cost you £2 / hour. Buy a machine for £500 that lasts 3000 hours and it will have cost you less than 17p / hour. In terms of performance an industrial quality unit will have a much greater cleaning power than domestic machine. This means you will spend a lot less time doing the cleaning and get a better result.

After sales service

As with computers the support that is offered after the purchase can be as important as the machine itself. Try to find a local dealer that stocks spares and accessories. A knowledgeable dealer will be able to fix faults without needing to send the unit away for days or weeks to a remote repair facility. Servicing will also be cheaper and faster with someone that doesn’t have to travel 100 miles to reach you.

To sum up.

Buy a quality machine suitable for the job required and from a local dealer.