Clothes washing machines

Last updated: August 21, 2009.

If there's one household appliance most of us simply could not do without, it's the clothes washer. If you ever been without your machine for a few days or weeks, you'll know just how hard it is to wash clothes by hand. Although clothes washers look pretty straightforward, they pull off a really clever trick: with the help of detergents, they separate the dirt from your clothes and then rinse it away. But how exactly do they work?

Photo: A typical European clothes washing machine, powered by electricity. This one is a front-loader: you put your clothes into that little circular window at the front. In the United States and Asia, top-loading machines are more common.

The parts of a clothes washer

Photo: Right: Inside a clothes washer drum. The paddles turn the clothes through the water. The holes let the water in (from above) and out (from below). The rubber seal stops water leaking out through the door.

The basic idea of a clothes washer is simple: it sloshes your clothes about in soap suds for a while and then spins fast to remove the water afterward. But there's a bit more to it than that. Think of a clothes washer and you probably think of a big drum that fills with water—but there are actually two drums, one inside the other.

The inner drum is the one you can see when you open the door or the lid. In a front-loading clothes washer, common in Europe, the drum stands upright. You push your clothes inside the door from the front and the whole drum rotates about a horizontal axis (like a car wheel). The drum has lots of small holes to let water in and out and paddles around the edge to slosh the clothes around. In a toploader, more common in the United States and Asia, you open a lip on top and drop your clothes into the drum from above. The drum is mounted about a vertical axis but doesn't actually move. Instead, there's a paddle in the middle of it called an agitator that turns the clothes around in the water.

Photo: Left: Clothes washing from yesteryear. This GEC electric washing machine, dating from 1935, was much more primitive than today's machines. There was no spinning to get the clothes dry: instead, you had to use a wringer (also called a mangle) fitted to the top of the machine (a pair of rollers through which you fed the clothes to squeeze out the excess water). This one is an exhibit at Think Tank, the science museum in Birmingham, England.

There's a second, bigger drum outside the inner drum that you cannot see. Its job is to hold the water while the inner drum (in a front-loader) or the agitator (in a toploader) rotates. Unlike the inner drum, the outer drum has to be completely water-tight—or you'd have water all over the floor!

The two drums are the most important parts of a clothes washer, but there are lots of other interesting bits too. There's a thermostat (thermometer mechanism) to test the temperature of the incoming water and a heating element that warms it up to the required temperature. There's also an electrically operated pump that removes water from the drum when the wash is over. There's a mechanical or electronic control mechanism called a programmer, which makes the various parts of the clothes washer go through a series of steps to wash, rinse, and spin your clothes. There are two pipes that let clean hot and cold water into the machine and a third pipe that lets the dirty water out again. All these pipes have valves on them (like little doors across them that open and shut when necessary).

Photo: Old versus new: Left: An old-style mechanical clothes washer programmer. The dial on the left selects the program. The dial on the right sets the wash temperature (it's effectively a thermostat). Right: A modern electronic programmer. These dials are mounted on a computerized programmer circuit. The countdown-display tells you how long in hours and minutes it will be before your washing is clean and ready to take out (one hour and two minutes in this case, for a 30°C wash with a very fast 1400rpm spin).

Step-by-step

All the important parts of the clothes washer are electrically controlled, including the inner drum, the valves, the pump, and the heating element. The programer is like the conductor of an orchestra, switching these things on and off in a sensible sequence that goes something like this:

1. You put your clothes in the machine and detergent either in the machine itself or in a tray up above.
2. You set the program you want and switch on the power.
3. The programmer opens the water valves so hot and cold water enter the machine and fill up the outer and inner drums. The water usually enters at the top and trickles down through the detergent tray, washing any soap there into the machine.

4. The programmer switches off the water valves.
5. The thermostat measures the temperature of the incoming water. If it's too cold, the programmer switches on the heating element. This works just like an electric kettle or water boiler.
6. When the water is hot enough, the programmer makes the drum rotate back and forth, sloshing the clothes through the soapy water.
7. The detergent pulls the dirt from your clothes and traps it in the water.
8. The programmer opens a valve so the water drains from the drums. Then it switches on the pump to help empty the water away.
9. The programmer opens the water valves again so clean water enters the drums.
10. The programmer makes the drum rotate back and forth so the clean water rinses the clothes. It empties the drum and repeats this process several times to get rid of all the soap.
11. When the clothes are rinsed, the programmer makes the drum rotate at really high speed—around 80 mph (130 km/h). The clothes are flung against the outside of the drum, but the water they contain is small enough to pass through the drum's tiny holes. Spinning gets your clothes dry using the same idea as a centrifuge.
12. The pump removes any remaining water and the wash cycle comes to an end.
13. You take your clothes out and marvel at how clean they are!