How Dishwashers Work

Obviously the purpose of the dishwasher is to take dirty dishes, wash them thoroughly, and in most cases in the United States, dry the dishes. While that is true, you may not be aware that there are several different types of dishwashers on the market. For example, there is the standard built-in under the cabinet made to fit a 24 inch wide space dishwasher. But did you know, some dishwasher manufacturers produce a dishwasher to fit into an 18 inch space? In addition to the standard built in dishwasher, some manufacturers produce a portable dishwasher. That is a dishwasher on wheels that can be rolled over to the kitchen sink and a hose snaps onto a special attachment on the faucet for the hot water inlet. That same hose also has a drain line on it for the dishwasher. Sometimes these dishwashers are portable only, and sometimes they can be converted to an under the counter dishwasher.

If you have a very small kitchen like an apartment kitchen, you can have an under the sink dishwasher. This type of dishwasher has been modified to fit under a sink so the upper rack is very small. That leaves the lower rack as the only real usable space with this dishwasher. There is also another type of dishwasher, a dishwasher sink combination. These units are usually designed to fit into a 48 inch space. They usually have a stainless steel sink and a drain board.

The components that make up a dishwasher are, the water inlet valve, the main dishwasher wash pump assembly, a timer or electronic control, a dispenser mechanism for the dish detergent, a door latch switch assembly, a heater, and on most model dishwashers today, a separate drain motor and pump assembly.

The main pump on a dishwasher usually sits below the floor of the dishwasher in the center. This pump circulates water through the water distribution system under moderate pressure. The water distribution system is mainly made up of the internal plumbing that connects the outlet of the pump to the upper and lower wash arms. Historically this main dishwasher pump assembly has been used to wash the dishes and, along with some sort of mechanical mechanism drain the dishwasher.

The Drain Pump Assembly
In more recent years, dishwasher manufacturers have started using a separate dishwasher drain pump assembly. The only purpose of this pump is to remove the water from the dishwasher when the timer or the electronic control sends a signal to it during the wash cycle, and at the end of the dishwasher cycle. The main pump assembly and the drain pump assembly will never operate at the same time.

The Water Inlet Valve
The water inlet valve on a dishwasher is connected to the hot water supply. It can have its own separate plumbing with a supply valve, but it can also be connected to the hot water side of the sink, since most of the time the dishwasher is right next to the sink. The water inlet valve has a coil of wire on the top that when energized electrically by the timer or the electronic control, creates an electromagnetic field lifting up a plunger allowing hot water to enter the dishwasher.

The Detergent Dispenser
The detergent dispenser is designed to open at a very specific time in the wash cycle. It can be controlled by a motor, solenoid, and often times by a wax motor. A wax motor is a device with a wax like substance inside that when heated expands and pushes a plunger. This allows the wax motor to be attached to almost anything that needs light mechanical work done. In the case of the dispenser, it is opening the door to allow the water within the dishwasher to wash out the detergent. In the past when dishwashers relied on timers, there were all kinds of mechanical devices associated with the timer, that opened the dispenser releasing the detergent.

The Door Latch Assembly
The door latch assembly on a dishwasher is designed to securely latch the door closed, pulling the gasket tight on the dishwasher cabinet to prevent leaks. The door latch assembly also has switch contacts that interrupt the circuit to the wash or drain motor, when the doors open.

The Dishwasher Heater
Dishwashers in North America are manufactured with a heater in the base of the dishwasher, under the bottom rack. The purpose of the heater is to help maintain the water temperature during the wash cycle, and dry the dishes at the end of the cycle. In the past when most dishwashers were made up of stainless steel, or porcelain, manufacturers could install a high wattage here. However, since most dishwashers manufactured for North America today are made using plastic tubs, the heaters under the lower rack are not very high in wattage and don't produce much heat. This leads to washability complaints, because the heater is not powerful enough to keep the water hot during the wash cycle. This low wattage heater also leads to the complaint of wet dishes at the end of the cycle. Dishwasher manufacturers say that you can operate a dishwasher that has a hot water inlet temperature of 120 degrees Fahrenheit. Most people find that 120 degree water does not wash dishes very well, and they wind up increasing the temperature on their hot water heater. Some dishwashers mostly high end dishwashers, have a separate heater in a chamber outside the washtub. This external heater assembly is a sealed unit within inlet and outlet port. This allows the pump assembly to push water in and out of the heater, to help maintain and even increase the water temperature. In an effort to save energy, dishwashers in Europe do not have heaters in the tub, although some high-end dishwashers use the external heater as mentioned above.

The Dishwasher Timer
A dishwasher timer is an electromechanical device with a motor, and a set of gears and cams that open and close switch contacts to control the various components within the dishwasher. The timer motor can be mounted on the outside of the timer, or it can be molded into the plastic housing of the timer.

The Dishwasher Electronic Control
The majority of dishwashers manufactured today use electronic controls instead of the old mechanical timer. This is because electronic controls are less expensive to manufacture, and in some ways are more dependable overtime than mechanical timers. Electronic controls on dishwashers use a low voltage to control relays that open and close switch contacts to the various loads on the dishwasher. A load is a device that consumes electricity. For example, the motor and the dispenser assembly are loads. Dishwashers that use electronic controls can have a thermistor that senses the temperature in the wash tub, to turn the heater on and off. Also a dishwasher that uses electronic controls, can have a sensor that interprets how dirty the water in the wash tub is. This permits the dishwasher from reducing the cycle time, thereby saving time and energy.