Lesson 6
How a Dishwasher Cleans
Follow one small batch of water round a dishwasher many times, and use that loop to fix gritty plates, cloudy glasses and a machine that stops with water in its base.
The same water, round and round
A dishwasher doesn't blast fresh water at your plates for an hour. For each stage it takes in a small amount, collects it in a sump at the bottom of the tub, and a circulation pump sends it up to the spray arms again and again. The water hits the dishes, falls back to the sump and goes round once more.
The spray arms have no motor. Their jets are angled, so the water squirting out pushes each arm round, like a garden sprinkler spinning on the lawn. Anything that stops an arm turning, such as a tall pan handle or a blocked jet, leaves part of the rack unwashed.
A heating element like the one in Heating Elements and Trips warms that same water, and a drain pump like the one in Draining: Pumps, Filters and Siphons empties it at the end of each stage. A dishwasher is filling, heating, washing and draining in one small box.