Dishwashing Machines

Engineers have improved our standard of living, and dishwashers are one of several important home appliances developed by mechanical and electrical engineers.

1. How it Washes
2. Understanding the parts, photos of parts
3. History

Above: diagram: underneath a standard low cost dishwasher

1.) How it Washes

These are the cycles used to clean the dishes in most dishwashers, these cycles may vary depending on the model:

1.) Cold water is sprayed on the dishes to try to remove surface material 2.) Hot water from your home or building's hot water heater is sprayed on the dishes, soap is released at the proper time from the soap container in the door. Remember that a computer controls the timing of all these actions in today's dishwasher. This part of the cycle should remove most oils and greases. How soaps work > Water is recycled during this wash cycle, hot water from the home is pumped in, and on some models when it falls to the bottom of the wash cavity a calrod (also used in ovens) heats the water back up to the desired temperature which is around 150 F (70C). Water flows into the drain at the base and is pumped back up to the spinning arms to be used again. Fine filters prevent food material from getting sucked into the spray arm system. Note: in some dishwashers the heating element is not used until the end of the cycle when the water is really losing its warmth. In other dishwashers the heating element is only used in the rinse/sanitation cycle after washing. 3.) At the end of the cycle the wash water is pumped out by another pump (seen in our diagram above). The water passes through a one-way valve on its way out. Grease and particulates often jam this valve area and this is one of the first areas to inspect when troubleshooting your dishwasher. 4.) Fresh water with rinse aid (if you use this) is sprayed over the dishes to help in drying and reduce water spots on the dishes. Remember that in some dishwashers the calrod is only used in this rinse cycle to create very hot temperatures to help rinse and sanitize the dishes. 5.) In some models the heating element is also used to heat the air and remove humidity, therefore helping to dry the dishes faster.

High-end dishwashers:
There are MANY kinds of dishwashers besides the standard home model described above. Professional commercial dishwashers are really amazing pieces of machinery, some of which can wash dishes very quickly (1-3 minutes). Professional models can work well and fast but are often very noisy, require good water pressure, consume a lot of power, and require a power hood for the steam.

High-end consumer dishwashers for the home may have an inline water heater. This heater, which functions similar to a tankless hot water heater heats the water as it is pumped through to insure that the water is always hot. Some buildings may not give hot enough water so this is a good solution for people living with that problem.

2.) Understanding the Parts

Electric Parts of the dishwasher:
Electric Motors - used to operate water pumps. Learn more about motors >
Float switch - when the dishwasher first fills with water this switch activates when the water reaches a certain level, the control board than stops incoming water.
Solenoid - in plumbing related applications the word solenoid refers to a switch for water which is electromagnetically controlled. When power is present it is held open, when the power is switched off it closes, blocking incoming water. The solenoid is part of the "Water Inlet Valve". Heating Element - a calrod used to dry the dishes. It uses 300-950 Watts depending on the model. Learn more about heating elements >
Control Computer (Control Board) - the brain of the appliance. Learn more about control engineering >
Power Supply - conditions incoming grid voltage using transformers to desired levels for motors, computer and calrod. Learn more about transformers >

Below: induction motor (120V) with pump, this is the main pump.

Below: drain pump with copper coils exposed

Below: new calrod located inside drain assembly under the spray arm.

Below: lower spray arm

Below: plastic clear side chamber in a newer dishwasher, blockages can be seen more easily.

Below: not every dishwasher looks the same underneith, some are more difficult to work on than others.

3.) History

1886 - Josephine Cochrane develops the first effective dishwasher
1924 - The first modern dishwasher was invented by William Livens, it did not have the drying calrod.
1940 - The calrod was added to the dishwasher to assist in drying
1970s - Dishwashers become wide-spread in the US and Western Europe
2000s - 75% of homes in the US have dishwashers, penetration in some other markets is limited by low labor costs for hired help.

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