The pressure washer is connected to a water source (1) from which it draws cold water which, passing through a suitable filter (3), is introduced into a pump (10) driven by an electric or endothermic engine (11), i.e. combustion engine. If the water source supplies drinking water, it must pass through a "Backflow" device (2) necessary to prevent any backflow before reaching the pump.
The pump produces a high-pressure jet at the outlet, which is regulated and limited by a by-pass valve (12) before passing through a hose (13) and ending its path by exiting through a rigid lance (14) in whose head a nozzle (15) is fixed. A detergent from a tank (7) can be added to the water flow. The detergent can be introduced upstream (8) or downstream (9) of the pump.
If the detergent is added upstream of the pump (usually on machines with an internal water tank), this is called high pressure detergent delivery. In this case, the detergent is simply sucked in by connecting the hose (9) to the pump suction. The advantage obtained is that there is no pressure drop, but the foam effect is limited.
If, on the other hand, it is added downstream of the pump (8), we speak of low pressure detergent delivery. In this case, generally, the pump is supplied directly (6) from the water source (1): the detergent is sucked in through a Venturi system and an excellent foam effect is generated. However, the detergent is sucked in by a small nozzle that generates a drop in the pump pressure.
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