A friend had a petrol pressure washer and the psi was something silly. What gives these commercial units far more power than my Karcher?
Obviously I don't know the specific machines, but often, a decent pressure washer has a higher flow rate rather than higher pressure compared to a cheaper unit. My own Kranzle electric pressure washer is 150PSI, but compared to its predecessor, a Halfords one of the same pressure, it is much more powerful, and that's down to litres per minute, not PSI.
Karcher make a point of the low water usage in their adverts. The ability to remove dirt is all down to the energy in the water jet (e=mc2) as Einstein found. As the pressure is limited by pump design, most washers use a 3 piston squash plate pump, the only variable will be the water volume. The petrol powered washer is not limited to the electrical power available at a socket outlet, but the size of the petrol engine, which can be any size.
Bob is correct in his answer but it’s more like F=Ma, where force or kinetic energy in this case, is M, mass of water multiplied by a, acceleration. . So both volume of water and it’s speed at exit from the nozzle are important.
I rebuilt my mates old Honda engined washer, can't remember the manufacturer name of the pump but if I remember correctly they were Danish, had to wait a week for some of the non standard seals. Brilliant bit of kit, way better than any of the electric ones I've used though this one had the ubiquitous Honda GX160 engine four stroke, so loads of power. Engine was years old, only needed a new crank cos someone had continued to use it when the pump had rattled loose of the end of the crank and knackered the crank taper end. Engine was like new otherwise. Well worth spending £150 (free labour) on it than some new Chinese ****.
You can’t, hence they try to increase pressure so nozzle velocity goes up too. One solution is a tank, but you will only get short bursts, the time dependent on its volume.
So how do they work when I see chaps cleaning drives with a large jetwash in the back of the van. How do they get an increased flow?
they usually have a large plastic tank, which they fill between jobs. Usually gives them around 30 minutes. I have seen zip car service vans clean the alloys and then wash the body sparingly with a bucket.
Yes, as you can have as wide a pipe as the pump can handle, where as most domestic models are limited by a garden hose around 15mm in diameter but does have the benefit of arriving at some pressure where as the tank pressure is based on the volume of water above the outlet
Domestic karcher k2 Specifications Brand Karcher Cable length 5m Connection size 19.05mm Hose length 4m Maximum flow rate 360L/hr Maximum operating pressure 110bar Maximum operating temperature 40°C Power output 1.4kW Power voltage supply 240V Commercial washer Diesel Model: 30KLN+ES Max Pressure: 207 Bar / 3000 PSI Volume: 3.3 GPM / 15 LPM Pump: Heavy Duty Triple Piston Cat Pump Engine: Yanmar L100N Diesel Push Button Electric Start with recoil backup Drive: Triple V-Belt Drive Ensures long life on Engine/Pump Supply: Suction or Direct Feed Suction Hose: 4.5m 3/4" Quality Suction Hose, with Brendon SS Suction Strainer Delivery Hose: 15m 3/8" Double Braided Delivery Hose & Cplgs Weight & Dimensions: 147kg 1050mm x 680mm x 800mm the pump and motor are what counts as you can see from above Commercial unit way more powerful and costly Than domestic karcher. And will also do a lot more damage to things very easily. If you have low water pressure ( or commercial unit) you need a water tank eg household wheelie bin if your washer has a draw pipe fill up bin drop pipe in away you go check bin size for ltr holding and then washer ltr per minute use, that’s how long you can wash for don’t turn the hose off will increase wash time.
The water flow and PSI do go hand in hand, I was looking for a great comparable for replacing my electric version and wanted to upgrade. I found this article about petrol pressure washers which really helped clear up a lot of questions for me and ended up going with a Wilks USA one.