Hi James, great question. The cleaning power of a pressure washer is a combination of its pressure (PSI rating) and water flow rate (litres per minute).
Often people only consider the PSI number when looking at pressure washer models, but in fact testing shows that a greater water flow rate has a slightly greater influence on overall cleaning effectiveness:
- Increasing the PSI rating of a pressure washer unit by 10% will increase cleaning effectiveness by 7%
- Increasing the Water Flow Rate of a pressure washer unit by 10% will increase cleaning effectiveness by 12%
So when comparing pressure models, be sure to consider each model's PSI rating and its Water Flow Rate capacity.
Note there are obviously many other factors on a unit to unit basis which also influences a pressure washer's cleaning capabilty such as; water temperature capacity, type and make of pump, piston types, nozzle & gun types etc.