Dishwasher Basics: The Care and Feeding (and Some History) of Dishwashers: This article will be primarily about the Mark III mechanical dishwashing machine, but first a word about the original model.
The Mark I dishwasher is an able-bodied human with fully functional hands and eyeballs who cares enough about your comfort, convenience, and well-being to periodically scrub away the food residue from the dishes, glasses and utensils you use without breaking them. If you know what is good for you: tip them generously if you get the chance, particularly if he or she is not an employee of a restaurant but member of your household.
The Mark II dishwasher was a hand-cranked machine designed by a wealthy woman named Josephine whose servants were forever chipping her fine china (the importance of tipping generously cannot be understated). Her original design was put on display at the 1893 Chicago World Fair and she went on to found the company that became known as Kitchen-Aid [TM].
The Mark III dishwasher is a powered, fully automated box for washing dishes found in many home kitchens in industrialized countries. Persons lucky enough to have them simply load dishes into racks, add some detergent, shut the door and punch the ON button. A while later the box will contain clean dishes.
Dishwasher Innards: What Goes on Inside the Box (and What is All That Noise)? The first thing that happens is a pump activates and tries to pull water from your hot water supply lines into the machine. If the water in the lines is cold the water will be shunted to the drain line until it warms up. There is usually only one pump in a dishwasher but it connects to numerous valves and can send water wherever it needs to go.
Once hot water is available the basin at the bottom of the machine is filled and the heating element is activated to raise the water temperature further. An agitator will spin to mix the detergent while the water is raised to cleaning temperature. This is usually 160 to 185 Fahrenheit (73 to 85 Celsius). The pump activates again this time pulling very hot, soapy water from the basin and sending to rotating spray nozzles which are designed to thoroughly blast soiled dishes with high pressure jets of water from as many different angles as physically possible. Water that hits the dishes falls to the basin carrying particles of food residue with it. The pump continues to cycle the water for a set amount of time. Gradually the water gets dirtier but the dishes get cleaner. The next part of the cycle sees the pump pull the dirty water from the basin and send it to the drain. Most machines will activate some sort of grinding mechanism to deal with large chunks of hardened food to prevent the pump from ever getting clogged. Once the dirty water is gone the pump brings in fresh water from the supply lines, refills the basin and begins to rinse the dishes with clean water. This might be hot, warm or cool water depending on the settings selected before activation. The last phase is the drying cycle. The pump removes the rinse water from the basin and sends it down the drain. An air vent opens and the machine monitors the humidity while a small fan pulls humid air out. The heating element may activate again to speed the drying along. That was the basic cycle. Many machines will have numerous settings and cycle options most of which will limit the use of hot water and the heating element in order to conserve energy. The loudest noises will usually be the pump and the food grinding/disposal mechanism.