Understanding the Mechanics of Clothes Dryers

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Appliances

Do you have any idea about how a clothes dryer works? Kirill Rudenko / Getty Images

Clothes dryers are a common appliance in nearly every American household, with millions more being produced each year. They are cost-effective and reliable, and you’ll be surprised to know just how simple these machines really are. A clothes dryer consists of:

  • A rotating drum that holds the clothes.
  • An electric or gas-powered heater that warms the air drawn through the clothes as they tumble, consequently heating up the clothes and the water in them.
  • An exhaust vent that expels water from the dryer in the form of steam.

This edition of How Stuff Works will take apart a clothes dryer and explore how each system works. We’ll begin by tracing the air’s path through the machine, then observe how the tumbler and fan operate, and finally, we’ll examine the controls.­

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Airflow


Dryer airflow diagram

You may be aware that warm, moist air exits the dryer through a hole in the back which is usually connected to a vent outside. But where does the air enter the dryer?

Let’s follow the air’s path through the dryer. The air is drawn into the dryer through openings on the outside of the machine. One fan propels all the air through the dryer, but the fan is actually the last step in the process.

Here’s a brief summary of how the air flows through the dryer:

  1. The air enters the dryer’s body through a large hole in the front.
  2. It is drawn past the heating element and into the tumbler.
  3. It moves through the door and is directed downward through the lint screen.
  4. It passes through a duct in the dryer’s front and into the fan.
  5. The fan forces the air into the duct that leads out the back of the dryer, at which point it exits the house.

The first point of contact for the air is the heating element. After the air enters the dryer’s body, it is drawn through the heating element and into the clothing tumbler.


Heating element

This is a typical nichrome-wire heating element, like the one in a toaster (for more information on nichrome wire, see How Toasters Work). The heating element consumes a lot of power, usually 4,000 to 6,000 watts in most dryers.

The air is drawn through the heating element and into the openings at the back of the tumbler.


Metal stamping and heating element

The metal stamping on the right, with the large holes, ensures that air can only enter the tumbler after passing through the heating element.


Tumbler and door

Now, the hot air moves through the clothes in the tumbler and then through the openings in the door.


Ventilation in Dryers

The air moves through the holes in the door and exits through the large slot located at the bottom of the door leading to the lint screen. The air is drawn through the lint screen and moves down a duct located in the front of the dryer and enters the fan. The fan is a centrifugal device that flings air to the outside, sucking air from the center and pushing it out through the duct present at the back of the dryer. In the next section, we will explore what causes the tumbler to spin.


Tumbler in Dryers

Upon opening a dryer, you would be surprised to see that there are no gears on the tumbler. The tumbler is a giant gear or pulley, and a tiny pulley drives the motor. The ratio between the tumbler diameter and the motor pulley diameter eliminates the need for any gears. A thin belt is wrapped around the tumbler. The motor drives the small silver pulley visible beneath the black pulley in the image above. The belt loops through the silver pulley, the black pulley, and around the tumbler. The black pulley provides tension, and the spring tries to pull it back when the belt is hooked up, giving it tension. The same electric motor powers both the fan and the tumbler, with one output for the tumbler belt pulley and the other for the fan.

Tumbler in Dryers


Weight Support in Tumbler

Most dryers don’t have bearings to help the tumbler spin smoothly. The weight of the clothes is supported by a flange at the back of the tumbler, connected to a simple bushing that allows the flange to spin. The tumbler’s back bolts to this flange. The front of the tumbler rides on two white plastic pads mounted to the top of the support structure.

Controls in Dryers


Cycle Control Knob in Dryers

Unlike modern dryers, this dryer has no electronics. Instead, a system of gears, cams, electrical contacts, and motors creates a mechanical computer. The cycle control knob controls both the type of cycle and the duration. Let’s take a look at what’s inside this switch.

Cycle Switch

By rotating the knob to different positions, you can control the cycle type and duration. The back of the cycle switch has a little motor attached to it. The image below depicts the motor unscrewed from the switch.


Cycle Switch, Back View

The tiny gear on the motor turns slowly and engages a larger gear inside the switch, which rotates even slower.

The cycle switch mechanism is composed of four cams stacked on top of each other, each of which engages one of the four contacts in the switch. The motor turns the gear on the dial that is connected to the cams. The height of the bend in each of the contacts varies and is located at different heights inside the cycle switch box. The cams engage each contact in a counterclockwise manner, starting from the bottom left and going to the top left. The cycle switch determines the duration of the elements and the heating elements that are on at any given time. The heat-setting buttons control the heat settings for the timed dryer cycles. The buttons work with plates that make the tumblers engage and control the heating elements. There are two temperature shut-off switches to prevent overheating, one located near the lint screen and the other acting as a backup in case the first one fails. The front temperature sensor detects the temperature inside the tumbler and cuts the power if it gets too hot.

There is a second sensor located near the heating elements. In case the airflow is blocked, the air around this sensor will rapidly heat up to its trigger temperature, causing the sensor to shut off power.

Additional Information

  • Clothes Dryer Reviews
  • Purchasing a Clothes Dryer
  • The Dryer Page
  • Countertop Microwave Clothes Dryer
  • Installation of a Clothes Dryer
  • Venting a Clothes Dryer
  • Repair Clinic: Dryer Parts and Repair Advice

FAQ

1. What is a clothes dryer?

A clothes dryer is an appliance used for drying wet clothes. It uses heat to remove moisture from washed clothes and textiles. Dryers are commonly used in households, laundromats, and hotels. They come in various sizes and models, including electric and gas-powered dryers.

2. How does a clothes dryer work?

A clothes dryer works by using hot air to remove moisture from wet clothes. The dryer drum rotates, and the clothes are tossed around by the vanes. The hot air is blown through the drum, and the moisture from the clothes is evaporated. The moisture-laden air is then vented out through the dryer vent, and the dryer continues to heat and circulate fresh air until the clothes are dry.

3. What are the different types of clothes dryers?

There are two main types of clothes dryers: electric and gas-powered. Electric dryers use electricity to heat the air, while gas-powered dryers use natural gas or propane to heat the air. Electric dryers are more common and easier to install, while gas-powered dryers are more energy-efficient and cost-effective in the long run.

4. How do you maintain a clothes dryer?

To maintain a clothes dryer, you should clean the lint filter after every load of laundry to prevent lint buildup, which can cause a fire hazard. You should also clean the dryer vent regularly to ensure proper airflow. Additionally, you should check the drum and the vanes for any damage and replace them if necessary. Finally, you should have your dryer serviced by a professional technician at least once a year to ensure that it is functioning properly.

5. What are some safety tips when using a clothes dryer?

When using a clothes dryer, you should never overload it or leave it unattended. You should also avoid drying clothes that have been soaked in flammable liquids, such as gasoline or cooking oil. Additionally, you should never place items in the dryer that are not designed for it, such as shoes or toys. Finally, you should have your dryer vent inspected and cleaned regularly to prevent a fire hazard.

6. How can you save energy when using a clothes dryer?

To save energy when using a clothes dryer, you should always dry full loads of laundry, as it is more energy-efficient than drying small loads. You should also use the moisture sensor feature, which automatically shuts off the dryer when the clothes are dry, instead of relying on the timer. Additionally, you should use the low-heat or air-dry setting for delicate fabrics, as it uses less energy. Finally, you should keep the dryer vent clean and unobstructed to ensure proper airflow and efficiency.

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