Choosing the right pressure washer
Pressure washers are rated in two ways - by water pressure and water flow.
The water pressure rating measured in bars, indicates how much pressure is available for cleaning. Generally, the more pressure the machine delivers, the more power it has to lift dirt.
Beware the figures quoted in the adverts or printed on the box! They will invariably only quote pressure and then often in an exaggerated form. "Maximum Pressure 120 Bar" often means that the safety valve will open at 120 bar to protect the pump. You might find the flow-rate printed on the machine label.
The working pressure will be well below that. Commonly a machine that is advertised as 120 bar would actually have a working pressure of around 90 bar.
Here are some useage examples:
Light tasks - 100 bar
Garden equipment: furniture, tools, barbecues, compost bin
Medium tasks - 110 bar
Cars and other vehicles
Swimming pools, hot tubs and spa pools
Tougher jobs - 110-130 bar
Paths, driveways and patios
Brick, stone and concrete walls
How to Compare?
Roughly, an increase in flow rate of one litre a minute is equal to 20 bar in pressure.
If you do want to compare the performance of two machines you can use a simple calculation which will give you a figure known in the trade as the 'Cleaning Effect';
Cleaning Effect = Pressure (bar) x Flow (litres/min) / 600
This is a reliable guide when comparing two machines. However, a general guide is that the bigger the motor, the better the performance. The flow and pressure are divided by 600 just to give us a simple figure to work with. You won't find this figure on the box or in the instructions, it's a calculation you have to do for yourself.
The smallest domestic HPC's start at about 0.83 cleaning effect and go to a top of the range DIY machine at maybe 2. So a cleaning effect of 1.0 is just about OK; 1.5 is reasonable, and 2.0 is good.
Hire shop machines are going to be about 2.3, just about the most powerful motor you can run on 230 volt single phase.
A 13 HP Honda petrol machine can develop a cleaning effect of about 6.75.
A 3 phase, 415 volt, 25 amp machine, 200 bar at 30 litres/min develops a cleaning effect of 10. If you weigh less than 13 stone you couldn't physically hang on to one!
Dyno Rod? From about 15 cleaning effect. Biggest I've ever seem? 5,000 bar at 15 litres, cleaning effect of 125! Harness required and ballistic quality clothing. Used for concrete cutting.
How much power?
A more powerful pressure washer doesn't necessarily do a better job, it will do the same job in less time.
Cheap machines can perform as well as more expensive machines, but the major difference is in durability - how long the machine will last!
About two thirds of the cost of manufacturing a HPC is the motor. Cheaper machines will have universal (brush) motors, sometimes intended for vacuum cleaners! Better quality machines will have induction motors.
Typical 'total run time' on a universal motor in a HPC can be as low as 10 working hours. That means it's knackered after that time!
An induction motor, even a cheap one, will run for 50/60 hours, better quality induction motors will run for 100+ hours.
How can you tell? Price is a good guide, very cheap machines will have universal motors. Weight is a good guideline, universal motors are much lighter that induction motors. Noise is another clue, because of the RPM universal motors are extremely noisy.
As a comparison, industrial machines have motors rated at 800 - 1000 hours.
I bought a cheap Kinzo 60 bar pressure washer with an induction motor. It does not clean very well but it has lasted years. Go figure?