How do clothes dryers work

Both types utilize electricity for the controls and the motor that turns the drum. A large belt encircles the drum and rolls through a pulley on the electric motor.

Gas dryers are combustion appliances. When they burn gas, they give off deadly carbon monoxide gas that must be vented to the outdoors. Lint can be a serious fire hazard.

So all dryers should be connected to a noncombustible metal vent duct that routes from the dryer to an exterior wall. First of all, we have to look at the temperature shut-off switches these switches are designed to automatically shut-off your tumble dryer if your appliance reaches a certain temperature.

The switches can be placed in different areas depending on your model of tumble dryer although one is normally always placed near the lint screen. Temperature sensors are also a common safety feature one will be placed near the tumble and will detect the air temperature that blows into it.

If the temperature is too high then the sensors will cut power to the dryer. A second sensor is usually placed near the heating elements which will act as a back-up if the airflow inside your dryer is blocked or shut off. Namely, the controls for your tumble dryer, more advanced machines will use an electrical control panel which will program how hot the heating elements should get.

But older tumble dryers will use a series of plates which are connected to buttons that operate them. By changing the layout of the plates more or less air can be allowed into the tumble, therefore, making the heat cycle hotter or cooler, depending on what you press. But where does the air enter the dryer? Let's follow the path of the air through the dryer. The air is sucked into the dryer through openings in the outside of the machine.

One fan drives all of the air through the dryer, but the fan is actually the last step in the process. The first thing that the air hits is the heating element. After the air enters the body of dryer, it is sucked through the heating element, and then into the clothing tumbler. This is a standard nichrome-wire heating element, just like the heating element in a toaster see How Toasters Work for details on nichrome wire. This heating element consumes lots of power -- 4, to 6, watts on most dryers.

The air is drawn through the heating element and into the holes in the back of the tumbler. The metal stamping on the right, with the big holes in it, makes sure that air can enter the tumbler only after it has gone through the heating element.

The hot air now makes its way through the clothes in the tumbler , and then into the holes in the door. The air passes through the holes in the door , and out through the big slot in the bottom of the door which leads to the lint screen.

The air is drawn through the lint screen and down a duct in the front of the dryer , where it enters the fan. The fan is a centrifugal type of device -- as it spins, it flings the air to the outside, sucking air from the center and forcing it out the duct at the back of the dryer. In the next section we'll see what makes the tumbler spin. If you open up a dryer, one surprising thing is the lack of any gears on the tumbler.

It turns out that the tumbler is one giant gear or actually a pulley , and the motor drives a tiny pulley. Because of the ratio between the huge tumbler diameter and the tiny motor pulley diameter, no other gears are needed! A motor drives the small silver pulley that is visible beneath the black pulley in the picture above.

The belt loops through the silver pulley, through the black pulley and then around the tumbler. The black pulley provides tension -- when the belt is hooked up, the pulley is drawn off center, and the spring tries to pull it back. This gives the belt its tension. The same electric motor drives both the fan and the tumbler. The pulley for the tumbler belt is hooked up to one output of the motor, and the fan is hooked to the other.

Another funny thing about most dryers is that the tumbler has no bearings to help it spin smoothly. So what supports the weight of the clothes? At the back of the tumbler is a flange , connected to a simple bushing that allows the flange to spin. The back of the tumbler bolts to this flange. The front of the tumbler rides on two white plastic pads that are mounted to the top of the support structure.

This dryer has no electronics in it at all. Instead, a system of gears , cams , electrical contacts and motors forms a sort of mechanical computer. Let's start by looking at the cycle control knob. By turning this knob to various positions, you can control both the type of cycle and the length of time it runs.