Dishwasher

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A dishwasher is a mechanical device for cleaning dishes and eating-utensils. Dishwashers can be found in restaurants and private homes.

The mechanical dishwasher cleans by spraying hot water, typically between 55 and 75 °C (130 and 170 °F) at the dishes, with lower temperatures used for delicate items

After placing the dishes properly in the dishwasher, the detergent is placed in the dispenser, and the rinse conditioner is checked for the proper level. The door is closed, and the type of wash cycle is selected. The door latch holds the door closed and activates the door latch switch. This will complete the electrical circuit for the dishwasher to operate. If the door is opened during the cycle, this will cause all operations to cease.

The timer will energize the water inlet valve, and water will begin to enter the tub. The dishwasher does not fill with water like a washing machine. It is designed so that the tub does not have more than two gallons of water in it at any one time. Should the timer switch contacts fail to open during the fill cycle, a float switch assembly, located inside the tub, will open the electrical circuit to the water inlet valve at a preset level.

The fill safety switch is part of the float assembly. Should the timer fail to open its switch contacts, water will keep entering the tub until the float, located inside the tub, rises and engages the float switch to shut off the water. Note: The float switch will not protect against a mechanical failure of the water inlet valve.

During the wash and rinse portion of a cycle, the heater element heats the water (on some models) to at least 140 degrees Fahrenheit. This feature is built into the dishwasher and is designed to save the customer money on the operating cost.

The water is repeatedly pumped through the lower and upper spray arms and onto the dishes. As the water runs off the dishes and back to the pump, it flows through a filtering system. On some models, the filter is designed to separate most food particles from the water so that they aren’t sprayed back onto the dishes.

At the end of a wash or rinse cycle, the water is pumped out of the dishwasher, flushing the filter of any small food particles. The larger pieces of food are trapped on the pump guard, which must be cleaned out before the next use. On some models, the pump screen removes food particles from the water, stores them, and then grinds them up as they are washed down the drain. During grinding, some sounds will be heard. All dishwasher models have some type of mechanism to dispense a rinse aid agent during the designated rinse cycle. The rinse aid agent will not allow the water to stay on the dishes. This will improve the drying time and prevent spotting and filming on the dishes.

At the end of the cycle, the heater element comes on (if selected) and helps dry the dishes. Certain models have a fan that circulates the air to speed up the drying cycle, thus making sure that the dishes dry evenly. Some models have a cool-dry cycle. This allows the dishes to be dried without the heater element operating. Combined with the heated air within the tub (from the wash cycle) and the dishwasher door opened a little bit, it will cause the water that remains on the dishes to condense and roll off them.

Dishwashers are similar to automatic clothes washers. They apply three kinds of energy on the things to be washed. These forces are:

• Mechanical energy Water that is sprayed onto the dishes by the motor and pump assembly to remove the food particles. Detergent is added to aid in cleaning of the dishes.
• Heat energy Using hot water (120 to 140 degrees Fahrenheit) to liquefy the fats and greases on dirty dishes. If the water temperature falls below 120 degrees Fahrenheit, the customer must select the water heating option (if available).
• Chemical energy Detergent dissolves the fat and grease off the dishes and keeps the soils suspended in the water to be removed later in the cycle.

Rinse aids are added to the rinse cycle to prevent water spotting of the dishes and to prevent the water from clinging to the dishes. A rinse aid agent will allow the dishes to dry quicker.

Dishwashers perform four basic functions that are modified and put together in different ways to create the various cycles. The four functions are:

• Fill
• Wash/rinse
• Drain
• Dry

As with clothes washers, the only difference between the wash and rinse cycles is the presence of detergent in the wash water. The mechanical activities that make up a wash and a rinse cycle are basically the same function.

Unlike clothes washers, most dishwashers fill and begin to wash (or rinse) at the same time. The functions are put together in various ways to make up different cycles. For example:

• Normal wash cycle A single or double wash with several rinses and a dry.
• Heavy wash cycle Adds a wash to the normal wash cycle.
• Pots and pans Similar to the heavy wash cycle, but this cycle heats the water in the wash cycles and (on some models) also heats the rinse cycles. On certain models, the timer will not advance until the water temperature is 140 degrees Fahrenheit. This will extend the total time of operation. Depending on the model, the cycle time can increase from 15 minutes to 2 hours. (Check the use and care manual for exact details.)
• Light wash cycle This cycle is like the normal wash cycle, but minus a wash cycle.
• Rinse and hold Two rinses for holding dishes to wash later.

The kind and amount of dishwasher detergent that is used is an important part of getting the dishes clean. Different brands of dishwasher detergent contain different amounts of phosphorous, which works to soften water and prevent water spots. If the water is hard, you will have to use a detergent with a higher phosphorous content—above 12 percent. If the water is soft, you can use a low-phosphorous dishwasher detergent. Some areas restrict the phosphate content to 8 percent or less. This means that the customer will have to increase the amount of detergent used in those areas where the water is hard. This is done by adding 1 teaspoon of dishwasher detergent manually in the main wash cycle for each grain of water hardness above 12 grains (general guideline: minimum of three teaspoons) (water hardness is measured in grains):

• 0 to 3 grains for soft water
• 4 to 9 grains for medium-hard water
• 10 to 15 grains for hard water
• Over 15 grains for very hard water

If the hardness of the water supply is unknown, contact the local water department.

If you are using a concentrated detergent, then you should use half the amount recommended above.

If the water is above 15 grains, the dishwasher will not perform properly (spots and film will appear on dishes), and a water softener will have to be added to the dishwasher water inlet supply.

Always use automatic dishwasher detergent only. The use of soap, hand dishwashing detergent, or laundry detergent will produce excessive suds and will cause flooding and damage to the dishwasher.

To obtain the optimum cleaning performance from a dishwasher, the most important factor is loading the dishwasher properly. When placed in the dishwasher, the dishes should be positioned in relation to the wash action. The dirtiest side of the dishes should face the source of the water spray. Glasses, cups, and bowls should be positioned slanted and with the bottoms up to prevent any water from collecting on the bottoms.

Flatware should be loaded according to the manufacturer’s recommendations as stated in the use and care guide. Any metal items that are loaded into the dishwasher should not touch one another unless they are made from the same materials. Any contact from dissimilar metals could result in permanent damage to the item. Do not place the silverware or dishes crowded together; this will prevent the water from reaching all of the soiled items. Delicate items should be positioned on the racks so they do not move around and cause breakage or chipping.

For optimum cleaning, never overload the dishwasher.

The most common means of identifying your dishwasher is to classify it by type as listed below, and then look for a manufacturer's label on it. Model numbers from the label are critical to identification for exact parts matching and also for determining what features are provided on the unit.

• Built-in: These dishwashers connect to a home plumbing system and are typically installed beneath kitchen countertops.
• Portable/freestanding: Instead of permanently connecting to a home plumbing system, these dishwashers are equipped with wheels for transport to use when needed.
• Drawer: This type of dishwasher has a compact design similar to a filing cabinet and contains two dishwashing drawers that can operate independently of one another.
• Countertop: These dishwashers are about the same size as a microwave and are designed to sit on a kitchen countertop.
• Integrated: These are similar in function to built-in dishwashers but are typically hidden behind a door or panel that blends in with the kitchen's decor.
• Commercial: These are industrial appliances capable of washing a high volume of dishes and are typically used in restaurants.

• Wikipedia: Dishwasher