It is just a guide to compare machines (if you take the flow in lpm x Pressure in Bars and divide by 600) this will give you a number to compare machines – It’s not set in concrete but it’s not a bad guide.
Just to confuse you tho' . The machines you compare must be operating at the claimed out put.
So a ws202 /gx390 set up is claimed to be 200 bar @21lpm but in real life would be around 170bar @21 because the engine is not big enough.
Interpump quote for the pumps electrical horsepower…mechanical hp (what we use with an engine ) is different. So when inter pump quotes 10hp for a pump…it will need a 13hp "engine".
Adding to this a 13hp Honda gx390 engine is only about 11.5hp.
There are two "main" suppliers of GX390 /200 bar /21 LPM machines on the market . Jetmac and Q washers. ( I don't like either!) Although Q washers after sales is generally very good.
Pressure washers (the people) generally want to be bigger than the next company ,bigger tool (pressure washer) ,bigger nozzle,…bigger job. This does not mean the biggest pay packet.
These are only my opinions and somebody will be along to rip them apart shortly