Working of a Dishwasher

Taken From: http://aaa-applianceparts.com/dishwasher.htm

All dishshwashers work in pretty much the same way. To understand how they work, let's look at these three areas:

• The motor and pump system
• The controls, switches, valves, and solenoids
• The interior

The motor and pump system

Your dishwasher has at least one motor. It is attached to a pump, which forces the water up into the sprayer arms. During the drain cycle, it also pushes the water out of the dishwasher…down the drain. A few European dishwashers use two separate motors, one for spraying and one for draining.

The motor is behind an access panel beneath the dishwasher. Some models have reversible motors, others don't. We will also discuss two older types that are not used in the newer dishwashers.

• If the motor is reversible, it is mounted vertically right in the center bottom of the dishwasher with the motor shaft pointed up. The pump is mounted atop the motor, then attached to the underside of the dishwasher. When the motor runs one way, the dishwasher pumps water up to the spray arms; when it runs the other way, it drains the water.

• If the motor rotates in a single direction, it is mounted horizontally, with the motor shaft pointed sideways, near the center bottom of the dishwasher. The pump is mounted to the end of the motor. The top of the pump is then mounted to the underside of the dishwasher. When the motor runs, it pumps water to the spray arms. To pump water to the drain, a mechanical arm integrated with the pump and motor activates, which diverts the water to the drain.

• Two other, older systems are becoming "extinct," in that they are no longer made.

• One is a belt-driven system. Its motor is near the front right corner of the dishwasher. The pump is mounted to the underside of the dishwasher at the center, and a tube-shaped belt connects the motor and pump. The motor is reversible: when the motor runs one way, the unit pumps water to the spray arms. When it runs the other way, the motor drives the pump to push the water out to the drain.

• The other system's motor rotates in only one direction. It's mounted vertically, right in the center bottom of the dishwasher, with the shaft of the motor pointed up, with the pump mounted atop the motor. The pump is then attached to the underside of the dishwasher. When the motor runs, it pumps water to the spray arms. To pump water out to the drain, a valve, completely separate from the pump and motor is activated. It diverts the water to the drain.

The controls, switches, valves, and solenoids

A dishwasher has at least three, but often six or more controls, switches, valves and solenoids. We will discuss these:

• Timer
• Selector switch
• Water inlet valve
• Float switch
• Soap dispenser
• Rinse aid dispenser
• Drain solenoid
• Thermostat
• Soil sensors
• Door switch
• Drying fan
• Heating element

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Timer

Dishwashers have a timer behind the main control panel at the front top of the dishwasher, or behind the lower access panel. It is either a mechanical device like a simple clock, or it's completely electronic with just a digital readout. The timer runs the dishwasher in a pre-determined pattern. It provides the electricity to all of the dishwasher components at the correct time, for the correct length of time.

Selector switch

A dishwasher usually has one or more selector switches on the main control panel at the top front of the door. The switch(es) allow you to choose among wash cycles, drying cycles (heat or no heat), temperature of the wash or rinse, and so on. The switches tell the timer which cycle options to engage.

Water-inlet valve

At the bottom left or right of the dishwasher, there's a water-inlet valve behind the access panel. This valve lets water flow into the dishwasher for the wash cycle. It is usually attached to the hot-water supply line, and to a tube that is then attached to the left or right side of the dishwasher. When the timer sends electricity to the valve, it opens and lets water into the dishwasher. The valve stops when the water level trips the float switch or when the timer stops sending electricity to the valve.

Float switch

Dishwashers have something meant to keep them from overfilling. This is usually a small switch attached to a float--a float switch. The float, which is usually cylindrical, is inside the dishwasher at the bottom, usually on the left side. As the water level in the dishwasher rises, the float rises too. When it reaches a certain height, the float activates its switch, which cuts the electricity to the water inlet valve. If the water-inlet valve is defective, the dishwasher may overfill.

Soap dispenser

Dishwashers have a soap dispenser located on the inside of the door. When the timer cycle calls for the soap to be emptied into the dishwasher, it either sends electricity to a bi-metal switch that opens it, or it mechanically opens the soap dish.

Rinse aid dispenser

Some dishwashers have a rinse-aid dispenser on the inside of the door. When the timer cycle calls for the rinse aid to be emptied into the dishwasher, it sends electricity to a solenoid switch, which opens the dispenser and measures rinse aid into the dishwasher.

Drain solenoid

Beneath some dishwashers, there's a timer-activated drain solenoid (an electro-magnetic coil) that opens a drain valve, to drain the wash water through a hose and out to the house's plumbing waste system.

Thermostat

Dishwashers have one or more small, cylindrical thermostats. These are a bit larger in diameter than a dime and have two or more wires attached to them. They protect the dishwasher, dishes, and humans by turning off the heating element that heats the water or the air in the dishwasher when it has reached its pre-set temperature. The thermostat automatically re-sets when the temperature falls to a lower level.

Soil sensors

Many of the more-recent dishwashers use multi-component soil sensors, which continually monitor the wash water during the wash cycle. These sensors help the dishwasher to wash for the amount of time that is appropriate for how dirty the dishes are, rather than for a pre-set period. When the water becomes clear enough, the sensor signals the timer to continue with the next cycle.

Door switch

Dishwashers have a door (or door interlock) switch that--if properly functioning--shuts off the dishwasher when the door is open.

Drying fan

Some dishwashers use a small fan to blow air (or heated air) into the dishwasher to dry the dishes faster. If your machine has a drying fan, it's beneath the dishwasher, usually in the back right corner.

Heating element

Dishwashers have at least one heating element--which is often a circular black tube at the bottom of the dishwasher under the lower spray arm. The element usually assists in heating the wash and rinse water to the proper temperature and/or assists in drying the dishes. Some dishwashers have another heating element integrated with the drying fan, to warm the air blown into the dishwasher to dry the dishes.

The interior

The interior of a dishwasher is where the dishes go. It contains the dish racks, the spray arms, and/or the tower that sprays water at the dishes, the upper part of the pump assembly, and the water filter.