How a washing machine works (by Capitan Farloc)

Ever wondered what really happens inside a washing machine when it’s running? In this article, we explain in simple terms how a washing machine works, what its main parts are, and what they do. Understanding the basics can help you spot issues and maybe even handle a few DIY fixes on your own!

Introduction

The aim of this article is to explain, without too much fuss, the basic working principle of a washing machine.
Obviously, not all washing machines are the same; there are more complex ones and simpler ones. Some are controlled by an electromechanical selector/timer, while others are governed by an actual computer equipped with a microprocessor and a program that manages and oversees the entire washing cycle.
However, as I mentioned earlier, in the vast majority of cases, the operating principle and general rules remain the same.
If, at the end of the article, there is a need for more detailed information or you'd like to share any suggestions, there’s a dedicated discussion open in the “DIY Forum.”
<Come Funziona una Lavatrice - FORUM> (unfortunately the forum is only in Italian, but we try to answer also to messages written in English)

Outline of the Main Components of a Washing Machine

To provide an idea of all the key components inside a washing machine and how they interact during a washing cycle, I've put together a diagram, which I'm presenting below:

1. THE TIMER OR PROGRAM SELECTOR As can be seen in the diagram, the "heart" or perhaps more fittingly, the "brain" of the whole system is the "Timer" or "Washing Program Selector," which acts as the control unit for all the components. When a washing cycle begins, it is the timer that, based on information received from various sensors, controls and commands all the active components in the following sequence.
2. THE DOOR LOCK SENSOR AND ACTUATOR First, there is a sensor in the door latch to ensure it is properly closed. If it isn't, the washing cycle won't start, and the machine won’t operate. On the other hand, if the sensor detects that the door is securely closed, the washing cycle begins by sending a signal to another component within the locking system to prevent accidental opening before the cycle ends.
3. THE WATER INLET VALVE Once the door is locked, a "Solenoid Valve" is activated, which is essentially an electric tap that allows water to flow into the machine for washing.
4. THE DETERGENT DRAWER For washing, detergent is also necessary. That's why, before reaching the "Drum Tank," the water flows through a "Detergent Drawer."
5. THE WATER LEVEL SENSOR OR PRESSURE SWITCH From the detergent drawer, water flows into the tank containing the drum full of clothes to be washed. As the water level in the tank rises, it compresses air in a tube connected to a "Pressure Switch." This device uses the air pressure to detect when the water has reached the correct level and sends this information to the control unit, enabling the next operation.
6. THE MOTOR FOR THE DRUM ROTATION Now that the door is locked and water (with detergent) is present, the "Motor" starts rotating the drum, combining the mechanical action of garment movement with the chemical action of the dissolved detergent.
7. THE HEATING ELEMENT FOR WATER TEMPERATURE If required by the current program phase, the "Heating Element" is activated to warm the washing water. To prevent temperatures that could damage garments, a temperature sensor is included. In some washing machines, this is connected to a dial on the front panel, allowing users to select the desired water temperature. Once the set temperature is reached, the heating element is turned off.
8. THE DRAIN PUMP After a certain time (not coincidentally, the control unit is often called a "timer"), power is supplied to the drain pump to expel the now dirty water. The motor is powered differently to increase its speed, creating the "spin" effect that wrings out clothes and removes as much water as possible.

Once the tank is empty again, the control unit starts refilling it with water to begin the next washing cycle phase. This time, the detergent drawer is empty, as the detergent has already been dissolved, and the phase of "Rinsing" is performed using only water, which is no longer heated... and so on.

The Timer or Program Selector

This component, which nowadays is more accurately called the "Control Unit," used to be an electromechanical part in older washing machines (like the one shown in the photo). A small motor (the metal cap located behind the assembly) would rotate a series of shaped wheels stacked one on top of the other to form a cylinder. Each wheel, depending on its shape, was capable of opening or closing an electrical contact, thereby activating or deactivating a specific component (such as the solenoid valve, motor, heating element, pump, etc.) at a particular stage of the program. The motor was a special type, designed to rotate at a constant speed governed by the frequency of the mains current. This allowed it to function as a proper "timer," ensuring that the various phases of the washing cycle always adhered to their set durations.

Nowadays, the vast majority of washing machines use an electronic board equipped with a microprocessor (just like computers). This enables them to process a program stored in their internal memory, which manages the sequence of operations to be carried out. By using information provided by various sensors (such as the door lock sensor, water level sensor, and water temperature sensor), the machine is able to "know" when it’s time to proceed to the next operation and thus perform the washing cycles.

The Door Lock and Latch System

In this case, we are dealing with a component that performs two distinct tasks. The first is the "Door Lock Sensor," which checks whether the door is properly closed or not. This check is necessary because, for safety reasons, the washing program should not start with the door open. The second is the "Door Latch Actuator," which is activated by the Control Unit as soon as the washing cycle begins, preventing the door from being opened while the machine is running, again for safety reasons.

There are two things to keep in mind:

• First, the door lock remains engaged for about thirty seconds to one minute even after the washing machine is turned off, and this is normal. However, some older models also take a long time to activate, during which the machine will not start even if turned on... and this too is normal.
• Secondly, it sometimes happens that the door lock sensor does not function correctly. As a result, even if the door is closed, the washing machine won't start. In these cases, firmly closing the door can temporarily resolve the issue, but this is usually a sign that the component will soon need to be replaced.

If you'd like to learn more about the working principle of a door lock and latch system and how to check if it’s functioning correctly, refer to the dedicated article:
How the washing machine door lock system works (by Capitan Farloc)

The Water Inlet Solenoid Valve

Although the term "valve" might bring to mind old radios with "thermionic valves," the word actually refers to a fluid flow regulator—basically, just a tap. It goes without saying that a solenoid valve is, therefore, an electrically controlled tap, and it enables the washing machine’s control unit to manage the inflow of water into the drum. The solenoid valve in a washing machine is located at the connection point for the water inlet hose. In fact, the threaded part where the hose screws in is usually part of the solenoid valve itself. Another easily identifiable part of the solenoid valve is the "Solenoid" itself, to which two connectors are attached for the wires that control its activation. When current passes through it, a magnetic field is generated, attracting a metallic object (electromagnet), which performs the mechanical action of opening the "tap," allowing water to flow from the connected inlet hose into the rubber tube attached to the other end.

If you'd like to deepen your understanding of how a washing machine solenoid valve works and how to check if it’s functioning properly, refer to the dedicated article:
How a washing machine's solenoid valve works (by Capitan Farloc)

The Detergent Drawer

The tube that exits the solenoid valve naturally leads to the drawer where detergent for washing (or pre-wash, if required) is added, along with fabric softener and bleach, depending on the washing needs and chosen program. It is clear that water always passes through this drawer, but only during the first phase does it dissolve the detergent. In subsequent rinsing phases, the compartment will obviously be empty. The fact that there are multiple compartments, and that water flows through one or another depending on the washing phase, is controlled by a mechanism. In older washing machines, this was driven by a system of levers moved directly by the program selector knob as it turned, whereas modern machines use an electromechanical mechanism controlled by electrical signals from the control unit. The one shown in the photo is mechanical. At the top, you can see the linkage operated by the selector knob and the lever that directs water flow from one compartment to another. The type of pointer present at the center of the lever is used for "calibrating" the mechanism, but this is done at the factory during assembly and usually doesn’t need to be adjusted. Finally, exiting the detergent drawer is a tube that delivers water directly into the drum.

The Water Level Sensor or Pressure Switch

The water flowing from the open solenoid valve passes through the detergent drawer compartment and through the rubber tube located at the top of the drum tank, eventually falling in a "shower-like" manner onto the drum and the clothes it contains. However, when the water in the drum tank reaches the correct level, a message must be sent to the control unit so it can close the solenoid valve and continue with the washing cycle. The "sensor" responsible for checking when the water has reached the predefined level does so by using the pressure exerted by the water on the air within a small tube connected to the bottom of the tank. The sensor activates when the pressure corresponds to the desired water level. This is why the sensor is called a "pressure switch."

If you'd like to delve deeper into the working principle of a washing machine pressure switch and how to check if it's functioning properly, refer to the dedicated article:
The Washing Machine Pressure Switch: How It Works (by Capitan Farloc)

The Drum Rotation Motor

his is where the real "work" of the washing machine begins: the rotation of the drum. This movement is achieved by a motor connected via a belt to a pulley located at the back of the drum.
Typically, two types of motors are used in washing machines: the "Asynchronous Motor" and the "Brush Motor." Both have advantages and disadvantages. Broadly speaking, older washing machines primarily used asynchronous motors, while modern machines predominantly feature brush motors.

The difference between the two lies in their operation:

• The Asynchronous Motor rotates its rotor by exploiting a "rotating" magnetic field generated by the "phase shift" of the alternating current waveform, achieved with a capacitor. Depending on how the capacitor is connected, the electric field (and thus the rotor) can turn in either direction. This motor’s advantage is low maintenance; however, its drawback is that its speed depends on the frequency of the current it receives. This makes it challenging to achieve speeds other than those for which it was designed. As a result, washing machines with asynchronous motors typically have only two speeds—one for washing and one for spinning.
• The Brush Motor, on the other hand, has copper windings on its rotor, which act as electromagnets. Depending on how they are powered, these are attracted to or repelled by fixed magnets (or other electromagnets) mounted on the motor's outer frame (the stator). This configuration requires the use of "sliding brushes," which are graphite sticks pressing against rotating contacts on the rotor shaft and directly connected to its windings. This motor’s strength lies in its easy speed variability. However, its weakness is that the brushes wear out over time and need periodic replacement. Washing machines with brush motors typically allow for a range of spin speeds.

The Heating Element for Water Temperature

It’s well-known that detergent works better with hot water, and this is why washing machines are equipped with a heating element to warm the water. This heating element is only powered during the washing phase. Additionally, there is a dedicated Temperature Sensor that detects when the water reaches the set temperature and then turns off the heating element. Older washing machines often used one or two thermostat switches, limiting the choice to just one or two washing temperatures. Modern washing machines, however, offer a much wider range of temperature options, thanks to the temperature sensor, which is appropriately interpreted by the control unit.

The Drain Pump

Each phase of the washing cycle ends with the expulsion of the used water. To discharge the water through the outlet hose, a "centrifugal" pump is used. This pump, with the help of a spinning fan called an "impeller," rapidly rotates the water, forcing it upward through a tube and into the drainage system by centrifugal force. The draining operation is usually time-controlled. During the draining phase, the control unit keeps the pump running for a predefined amount of time, knowing that this duration is sufficient to empty the drum tank of the loaded water. As a result, there is generally no "emptying" sensor to halt the pump. Located at the front of the pump is typically a filter designed to catch any objects that may have fallen into the drum tank. This filter is sealed with a cap that is accessible from the outside of the washing machine. It is usually situated at the lower front section and often covered by a plastic panel, which must be removed to disassemble and clean the filter.

I hope this article has been helpful in clarifying how a washing machine works.
For questions, further explanations, or even just to let us know you enjoyed the article, feel free to contribute to the discussion specifically opened on the forum:
<Come Funziona una Lavatrice - FORUM>

Thank you
Luciano (Capitan Farloc)