The specification most beginners get wrong, and why the biggest number on the box is the least useful one.
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Cleaning power is a function of pressure and flow together. Beginners buy pressure. Professionals buy flow.
## Pressure (PSI / bar) Pressure cuts. It breaks the bond between the dirt and the surface. Beyond a point, more pressure just damages the substrate — it does not clean faster.
## Flow (litres per minute) Flow carries. It moves the loosened dirt away and rinses the surface. Flow is what makes a machine fast.
Two machines, same 3000 psi: one at 8 L/min, one at 15 L/min. The 15 L/min unit cleans a driveway in roughly half the time. Same pressure, double the productivity — that is your hourly rate.
## Cleaning units A rough comparison figure: PSI x LPM = cleaning units. It lets you compare machines on one number. - Domestic big-box unit: 2000 psi x 7 L/min = 14,000 - Entry prosumer: 3000 psi x 10 L/min = 30,000 - Working commercial: 4000 psi x 15 L/min = 60,000
## Pump types - Axial (direct drive): cheap, spins at engine speed, gets hot, dies under continuous use. Fine for occasional work, wrong for a business. - Triplex (gearbox or belt reduction): runs slower and cooler, rebuildable, lasts thousands of hours. Annovi Reverberi, General Pump and Comet are the names to look for in Australia. This is what you buy.
## Petrol vs electric Petrol for mobile work — you cannot rely on a customer's power, and 15 L/min needs more than a domestic circuit can give. Electric only for indoor, enclosed or noise-restricted commercial work.
## Hot water Hot water dissolves grease and halves the chemical needed on organic growth. It is also expensive, heavy and only necessary for commercial food, grease and industrial work. Not a first purchase.