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Inside a dishwasher
A small pump that reuses the same few litres of water over and over — and spins the spray arms by itself.
- Water per cycle
- about 10–15 litres (modern machines)
- Pumps
- usually two: wash and drain
- Spray arms
- turned by the water jets themselves
- Impeller
- small, plastic, radial
Numbers are rounded, typical values — real machines vary.
The same water, again and again
A dishwasher lets in only a few litres of water, heats it, and a wash pump sends it up to the spray arms. The water rains back down into a sump, through a filter, and is pumped round again — for many minutes.
At the end, a separate small drain pump empties the machine. Its impeller is the part that gets jammed by broken glass or olive stones.
Spray arms that spin themselves
The spray arms have no motor. Their nozzles point slightly sideways, so the water jets push the arm round — like a garden sprinkler, and like a tiny driven by the pump’s water.
Physics you already know
The pump makes ; the narrow nozzles turn it back into speed (). And the rule tells you why tiny holes make fast, hard-hitting jets.