How does a Dishwasher Work?
Basically, a dishwasher is a robot that cleans and rinses dirty dishes. Humans have to load the dishes, add detergent, set the proper washing cycles and turn it on, but the dishwasher accomplishes a whole series of functions by itself. A dishwasher:
Fills itself with water
Heats the water to the appropriate temperature
Automatically opens the detergent dispenser at the right time
Shoots the water through jets to get the dishes clean
Drains the dirty water
Sprays more water on the dishes to rinse them
Drains itself again
Heats the air to dry the dishes off, if the user has selected that setting
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In addition, dishwashers monitor themselves to make sure everything is running properly. A timer (or a small computer) regulates the length of each cycle. A sensor detects the water and air temperature to prevent the dishwasher from overheating or damaging your dishes. Another sensor can tell if the water level gets too high and activates the draining function to keep the dishwasher from overflowing. Some dishwashers even have sensors that can detect the dirtiness of the water coming off the dishes. When the water is clear enough, the dishwasher knows the dishes are clean.
In this article, we’ll discuss exactly how a dishwasher gets the job done, how to use one properly and what features to look for when buying a dishwasher.
Inside a Dishwasher
Although dishwashers are watertight, they don’t actually fill with water. Just a small basin at the bottom fills up. There, heating elements heat the water to 130 to 140 degrees Fahrenheit. Then a pump propels the water up to the water jets, where it is forced out and sprayed against the dirty dishes. Think about a garden hose with no nozzle – if you put your thumb over the end of the hose, decreasing the space for the water to come out, it sprays out more forcefully. The dishwasher’s jets work on the same principle. The force of the water also makes the arms that hold the spray jets rotate, just like a lawn sprinkler.
When the washing and rinsing is finished, the water drains down to the basin again, where the pump propels the water out of the dishwasher. Depending on the type of dishwasher, the drain water might go right into the pipes under your sink, or travel up a hose into your sink itself.
The final step in a wash cycle is optional – the dry cycle. The heating element at the bottom of the dishwasher heats the air inside to help the dishes dry. Some people just let them dry without heat to save energy.
The main parts of a dishwasher are:
The control mechanism is located inside the door behind the control panel. Many units use a simple electro-mechanical system: a timer determines how long each part of the cycle lasts and activates the proper function at the proper time (such as the detergent dispenser, wash spray and draining functions). Units that are more expensive might have a computerized control system. Modern units also have a door latch that must be closed for the unit to run. Some also have child safety locks.
This is where water from the home’s water supply enters the dishwasher. The unit’s pump doesn’t pump the water into the basin – when the intake valve opens, water pressure drives the water into the unit.
An electric motor powers the pump. During the pump cycle, the pump forces water up into the spray arms. During the drain cycle, the pump directs the water into the drain hose. The motor-pump assembly is mounted beneath the basin, in the center of the dishwasher. There are two main types of pump:
These pumps switch between pumping water to the spray arms and pumping water to the drain by reversing the direction of the motor. Reversible pumps are usually vertically mounted.
The motor runs in one direction, so the direction of flow is switched from spray arms to drain by a solenoid that opens and closes the appropriate valves or switches one hose connection to another. Non-reversible pumps are usually horizontally mounted.
Dishwashers can be installed in either a portable or a permanent configuration. Portable units have finished sides and top that can be used as a countertop. When not in use, the machine sits in place next to the wall. When it’s time to run a cycle, the unit can be rolled on casters over to the sink, where it connects to the faucet and plugs into a nearby outlet. In a permanent installation, the dishwasher goes underneath the existing countertop and bolts into place. Hoses underneath the kitchen sink connect directly to the hot water line and the drain line, and the unit usually plugs in under the sink as well. Both types of installation require a 120-volt grounded line.
A portable dishwasher connected to a faucet and ready to run