Choosing a Pressure Washer, Performance – Part 2

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.

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 assess 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 lance attached. 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.


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