How does an automatic washing machine choose water level?

Automatic washing machines have sensors that calculate the ideal amount of water to use for each load. These sensors use the load’s weight and pressure to determine how much water should be used during a given cycle. Based on the wash cycle settings, the machine automatically fills the tub with the optimal amount of water using pre-programmed detection logic.

So, in simple terms, the water level in the washing machine is decided as per the size of the load, the type of fabrics, and the cycle you want to run.

This is done with the help of a few built-in sensors.

The load-sensing device senses the load and signals the pressure switch to fill the right amount of water into the machine.

The water level is controlled by the pressure switch or the level sensor in automatic washing machines and it works by using a small tube attached to it to regulate the level of water pressure in the machine.

When the water reaches a certain level, the pressure switch will start sensing it.

It will either send a signal to start the motor or open the inlet valves to draw more water until the desired level is reached.

Once the washer has been filled with the necessary amount of water, the pressure switch will turn off the motor or the inlet valves, preventing overflow or flooding.

Key Takeaways 

  • An automatic washing machine has built-in sensors to detect the size of the load as well as the water pressure level.
  • It makes use of pre-programmed logic to fill the water based on the load type, size, and cycle.
  • The amount of water that needs to be filled is sensed by the water level sensor as per the load. These sensors ensure that there’s no overfilling or underfilling of the washtub for a particular wash cycle.
  • The sensors in an automatic washer are not only active during the initial washing but also work during the rinse cycle or any other cycle that requires water or draining.

Technical explanation on how washing machine choose water levels

Load size and pressure measurement

  • Load-Sensing Device: At the heart of the system is a load-sensing device that measures the weight of the laundry load. This sensor is often located near the bottom of the washing drum. When the machine starts, it assesses the weight of the load by measuring the force exerted on the sensor.
  • Signal Transmission: The load-sensing device sends a signal to the central control unit, which interprets the load’s weight. This information is crucial in determining the amount of water required for effective cleaning.
  • Pressure Switch: Automatic washing machines are equipped with a pressure switch or level sensor. This switch monitors the water pressure inside the machine during different stages of the wash cycle.

Calculating Water Level

  • Initial Water Filling: When the wash cycle begins, the pressure switch or level sensor detects the initial water level. It compares this level to the desired water level for the specific load and cycle.
  • Pressure Changes: As water fills the drum, the pressure inside the pressure tube increases proportionally to the water level. The pressure switch constantly monitors these pressure changes.
  • Adjustment and Control: Based on the load weight and desired water level, the washing machine’s control unit calculates the rate at which water should be added. The pressure switch informs the control unit about the current water level, allowing it to make adjustments.
  • Motor and Valve Control: Once the calculated water level is reached, the pressure switch sends signals to control the washing machine’s motor and inlet valves. If more water is needed, the motor or valves are activated to maintain the desired water level.

Overfill and Underfill Protection

  • Overflow Prevention: The pressure switch acts as a safeguard against overfilling. If the water level approaches a critical point, the pressure switch signals the machine to stop adding water.
  • Preventing Underfill: Conversely, if the water level is lower than desired, the pressure switch can prompt the machine to add more water until the optimal level is achieved.

Continuous Monitoring

  • Rinse Cycle: The pressure switch continues to monitor water levels during the rinse cycle. It ensures that the correct amount of water is used for rinsing, maintaining washing quality.
  • Agitation and Draining: During agitation, the pressure switch temporarily stops water filling. When draining is necessary, the pressure switch detects the water level drop and signals the machine to initiate drainage.

Ensuring Accuracy and Efficiency

  • Calibration: Washing machines are calibrated to provide accurate weight and pressure readings. Regular calibration ensures that the sensors maintain their accuracy over time.
  • Algorithmic Logic: The control unit employs complex algorithms to convert sensor data into precise water level adjustments, optimizing water usage and energy efficiency.

Examples of Water Level Determination

Load Types

  • Light Load (T-shirts): For a load consisting of a few light items like t-shirts or socks, the washing machine’s sensors detect the low weight. As a result, the machine adds a relatively small amount of water to cover the load adequately.
  • Heavy Load (Towels and Jeans): In the case of a heavy load with items like towels, jeans, or bulky fabrics, the sensors detect a higher load weight. The machine calculates that more water is needed to ensure effective cleaning and even distribution.

Wash Cycles

  • Delicate Cycle: During the delicate cycle, where gentle washing is required, the sensors adjust the water level to be lower. This prevents excessive agitation and minimizes the risk of damaging delicate fabrics.
  • Normal or Heavy Cycle: In regular or heavy wash cycles, the sensors allow for a higher water level to accommodate thorough cleaning. More water helps agitate the laundry and remove dirt and stains effectively.

Water level based on fabric materials

  • Heavy Fabrics (Denim): Heavy fabrics like denim require more water to ensure thorough cleaning. The sensors detect the fabric’s weight and adjust the water level accordingly to penetrate and clean the dense material.
  • Light Fabrics (Silk or Lingerie): For delicate fabrics like silk or lingerie, the sensors ensure that a lower water level is used to prevent excessive friction. This protects the fragile fabrics from damage.

Water level selection based on mixed loads

  • Mixed Load (Various Items): When a load contains a mix of fabrics and sizes, the sensors work collectively to calculate an average weight. The water level is adjusted to cater to the heavier items while still being gentle enough for delicate ones.
  • Optimal Distribution: The sensors also aim to distribute the water evenly across the load, ensuring that all items receive adequate exposure to detergent and agitation for thorough cleaning.

Water Efficiency Considerations

  • Efficient Water Usage: In line with environmental concerns, modern washing machines strive for water efficiency. If the sensors detect a smaller load or a lighter fabric, the machine minimizes water usage while maintaining effective cleaning.
  • Load Size Awareness: The sensors prevent wastage by avoiding excessive water filling when the load is smaller. This not only saves water but also reduces energy consumption during heating.

Does the pressure switch control the water level during the rinse cycle?

Yes, the water pressure switch also controls the water level during the rinse cycle.

In other words, whenever the washing machine needs to fill with water or drain the used water, the water level will always be controlled by the pressure switch.

At the initial stage, once the pressure switch allows the washing machine to fill with a specific amount of water, it will begin to agitate or tumble the clothes inside.

After agitating for a certain amount of time, depending on the cycle selected, the washing machine will then drain out all of the used water.

If the water is successfully drained, the pressure switch detects this, and only then will it allow refilling the washtub with clean water for rinsing.

Finally, when the required level is reached, the pressure switch will stop the water from filling, and then the rinse cycle will resume.

This process will be repeated until the soap residue is removed from the clothing and no more suds are produced in the drum (another sensor detects the sud levels).

If the suds level is too high, the washer will keep repeating the rinse cycle and keep the pressure switch active throughout the process.

Finally, once all of this is done and all of the clothes are clean, your washing machine will drain out any remaining liquid and spin dry your clothing to get rid of excess moisture.

This helps ensure that your clothes come out dry and ready to wear after each cycle.

So, programmatically, all the above actions happen in a proper and well-defined sequence.

Final Thoughts

Now that you know how your washing machine calculates the optimal water level based on load size and fabric type, you can use it more effectively and worry-free.

The washing machine pressure switch is a vital component of a washing machine and is responsible for ensuring that the right amount of water is used during the laundry cycle.

Additionally, when the pressure drops below a certain point, this will also trigger the switch to shut off the motor, stopping any more water from entering the machine.

Next time you do a load of laundry, remember that there is a lot more going on inside that machine than just filling it up with water and draining it later.

Frequently Asked Questions

Do washing machines adjust water level?

Yes, many modern washing machines have the ability to adjust the water level based on the size of the load. This is typically done through the use of sensors that detect the amount of laundry in the tub and using air pressure to determine the appropriate water level needed for optimal washing.

Does fully automatic washing machine use more water?

The amount of water used by a washing machine depends on several factors such as the size of the load, the cycle type, the type of fabric, and the efficiency of the machine. So, the efficiency may vary depending on the model and type of your washer.

Why doesn’t my washer fill up with enough water?

If your washer isn’t filling up with enough water, it could be due to a clogged filter, faulty water inlet valve, low water pressure, or issues with the load size or sensors. Try basic self-troubleshooting like cleaning the washer and checking the water pressure levels. If nothing works, contact a professional for assistance.

Manish Singh is an expert in electrical engineering with a Diploma in the field. With over 12 years of experience, he specializes in repairing music systems, washing machines, dryers, and other laundry-related appliances. His in-depth knowledge in electrical repairs and decent knowledge about garment care makes him a trusted authority in the field of appliance repair and laundry related topics. If you have any questions or need assistance with your appliances, you can reach out to Manish through email: manish.singh (at)