How Does a Pressure Sensor Work?
Pressure sensors are measurement devices for detecting changes in applied pressure from a contained volume of liquid or gas. In appliances, they’re often used to detect water level in products such as washing machines and dishwashers. Pressure sensors are also used in furnaces to detect the combustion air flow through the furnace to the outside of your home. If the furnace inducer fan isn’t flowing combustion exhaust air out through exhaust flue, the furnace shuts down to prevent carbon monoxide from accumulating inside your home. Carbon monoxide and other combustion exhaust gases are dangerous and harmful to your health.
In this article, we’ll answer the question how does a pressure sensor work in washers, dishwashers and furnaces.
KEY TAKEAWAYS
- A pressure sensor detects water level in washers and dishwasher so the control system fill the appliance with the right amount of water.
- An air tube connected to the bottom of the tub attaches to the pressure sensor and pushes up on a diaphragm inside the pressure sensor to detect water level.
- An air pressure sensor in a furnace is a safety device that makes sure combustion exhaust gasses (including carbon monoxide) are properly blown out through the exhaust flue.
How Does a Pressure Sensor Work in a Washer?
The pressure sensor in a washer detects water level so the washer fills to the proper level without overfilling.
Washers typically use 1 of 2 different types of water level pressure sensors – a water level pressure sensor and a water level pressure transducer. Here’s how each type works.
How a Water Level Pressure Sensor Works in a Washer
The basic working principle of a water level pressure sensor in a washer is that any change in water level will cause a proportional applied pressure to the sensor. This will cause a physical reaction in the sensing element of the device that accurately measures water level in the washer tub.
A basic water level pressure sensor uses an air-tight tube connected to the bottom of the washer tub to transmit air pressure to the water level pressure sensor in the console or control area at the top of the washing machine. As water fills the washer, air transmitted through the tube exerts pressure on the diaphragm membrane of the water level pressure sensor and physically moves a reed attached to that device that engages a switch contact inside to sensor to indicate that the water level has reached the desired level in the washer tub.
When the water level pressure sensor detects that the desired water level is reached, the control system shuts the water valves to stop filling the washer. The drive motor kicks in to agitate or tumble the clothes and wash the load.
What Can Go Wrong?
A crack or hole in the air-tight tube that attaches to the bottom of the wash tub and the water level pressure sensor will prevent air pressure from pushing up on the membrane of the sensor so the pressure sensor will continuously detect that the tub is empty and water will overflow the washer – creating a flood in your laundry room.
Replace the water level pressure switch air tube when it has a crack or air leak.
A leak in the diaphragm the moves up as the washer fills can also prevent the washer from detecting when the washer is full. The same symptoms as above will occur when a leak in the diaphragm occurs.
You’ll need to replace the water level pressure switch when the component doesn’t detect water level accurately.
Other components and problems can prevent a washer from filling. For additional tips on troubleshooting a washer that won’t fill, view this helpful video:
If you’re unable to resolve a washer filling issue on your own, schedule washer repair and we’ll fix the washing machine for you.
How Does a Washer Water Level Pressure Transducer Work?
A washer water level pressure transducer works in a similar manner to a water level pressure sensor but a transducer creates an electronic signal instead of activating an internal switch in the component. As the washer fills with water, air in the sensor air tube pushes up on a diaphragm and moves a rod or piston inside of a core in the transducer to create an electronic signal that is sensed by the control board to control water level in the washer tub.
The electronic control board stops filling the washer and advances to the wash cycle when it senses that the washer tub is full based on the signal from the water level pressure transducer.
What Can Go Wrong?
A crack or leak in the pressure transducer air tube can prevent the water level pressure transducer from sensing that water level is increasing in the washer. When the electronic control board detects no change in the transducer signal, the washer typically stops filling and signals an error code on the control panel.
When your see an error code on the control panel, follow the expert troubleshooting tips in the washer error code chart for your machine.
When you’re unable to find and fix the cause of a washer error code, schedule washer repair service to resolve the issue.
How a Dishwasher Water Level Pressure Sensor Works
Some dishwashers use a water level pressure sensor to detect water level inside the tub. The water level sensor in a dishwasher works the same as the one used in a washing machine. An air-tight tube connects to the bottom of the dishwasher tub and the pressure switch. As the dishwasher tub fills with water, the air in tube pushes up on a diaphragm inside the pressure switch and activates a switch when the tub is full of water. The water stops filling and the control starts the pump motor to send water through spray arms to wash the dishes.
A leak in the air tube or a failed water level pressure sensor can prevent the dishwasher from filling or cause the dishwasher to overfill.
When you encounter filling problems with your dishwasher, many different components can be at fault. View this helpful DIY video to see expert tips on fixing a dishwasher that won’t fill:
If you’re unable to resolve a fill problem in your dishwasher on your own, schedule dishwasher repair service to have a Sears Home Services technician visit your home and fix the issue.
How Does a Furnace Pressure Sensor Work?
A furnace pressure switch is an automatic safety feature located near the motor. It shuts the furnace down if it detects that the inducer fan isn’t forcing combustion exhaust air out through the exhaust flue. This protects your home from accumulating dangerous combustion exhaust fumes including carbon monoxide.
This pressure sensor works in a similar manner to the ones described above except that this furnace sensor detects air pressure instead of water pressure. A diaphragm in the furnace pressure sensor moves and engage a switch when it senses that the inducer fan is properly blowing exhaust air out of the flue. Once the switch in the pressure sensor is activated, the furnace will start heating. If exhaust air flow stops due to a failed inducer fan or clogged exhaust flue, the furnace will shut off.
If your furnace won’t start, the furnace pressure sensor could be bad or the furnace could have other failures preventing it from operating. When your furnace isn’t working, schedule HVAC repair and we’ll send a Sears Home Services technician to your home to fix the problem.
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Glossary Terms
Wattage is the measure of electrical power expressed in watts (W), indicating the rate at which a device consumes energy.
A washer screw is a fastening device that combines a screw and a washer, designed to distribute the load of a screwed fastening more evenly and to prevent the screw from loosening under vibration.
A voltage meter, commonly referred to as a voltmeter, is an instrument used for measuring the electrical potential difference, or voltage, between two points in an electrical or electronic circuit.
A multimeter is an electronic measuring instrument that combines several measurement functions in one unit, commonly used to measure voltage, current, and resistance.
Common Appliance Symptoms
The most common reasons your Whirlpool washer won't stop filling are a clogged water valve, a bad water-level pressure switch, or a malfunctioning electronic control board.
The most common reasons your Whirlpool washer won't spin or drain are a seized gearcase, a broken motor, or a failed door switch.
The most common reasons your Whirlpool washer won't turn off are a malfunctioning electronic control board, broken motor or a jammed door lock assembly.
The most common reasons your Whirlpool washer won't start cycle are a malfunctioning electronic control board, jammed door lock assembly or a faulty user interface.
The most common reasons your Whirlpool washer vibrates are a damaged suspension rod, malfunctioning electronic control board or a dead fan.
The most common reasons your Whirlpool washer is experiencing the rinse cycle not working are a broken lid switch, a bad water-level pressure switch, or a malfunctioning electronic control board.