Present-day machines feature a drop-down front panel door, allowing access to the interior, which usually contains two or sometimes three pull-out racks; racks can also be referred to as “baskets”. In older U.S. models from the 1950s, the entire tub rolled out when the machine latch was opened, and loading/removing washable items was from the top, with the user reaching deep into the compartment for some items. Today, “dish drawer” models mimic this style, while the half-depth design eliminates the inconvenience of the long reach that was necessary with older full-depth models. “Cutlery baskets” are also common. A drawer dishwasher, first introduced by Fisher & Paykel in 1997, is a variant of the dishwasher in which the baskets slide out with the door in the same manner as a drawer filing cabinet, with each drawer in a double-drawer model being able to operate independently of the other.
The inside of a dishwasher in the North American market are either stainless steel or plastic. Stainless steel tubs resist hard water, provide better sound damping, and preserve heat to dry dishes faster. They also come at a premium price. Older models used a baked enamel on steel and are prone to chipping and erosion; chips in the baked enamel finish must be cleaned of all dirt and corrosion then patched with a special compound or even a good quality two-part epoxy. All European-made dishwashers feature a stainless steel interior as standard, even on low end models. The same is true for a built-in water softener. The flutes (Or valve meters) of the dishwasher are prevalent in American models (With some appearing in European and Asian models influenced by US design) due to the higher pressure of the American water system (which averages at 90 torrs/min, as opposed to the 65 torrs/min pressure in other countries). The flutes help drain the excess water, preventing entropy within the system due to higher pressures at a lower volume. This is a removable fixture, as some areas require a higher or lower discharge based on their water system.
Mid-to-higher end North American dishwashers often come with hard food disposal units, which behave like miniature garbage (waste) disposal units that eliminate large pieces of food waste from the wash water. One manufacturer that is known for omitting hard food disposals is Bosch, a German brand; however, Bosch does so in order to reduce noise. If the larger items of food waste are removed before placing in the dishwasher, pre-rinsing is not necessary even without integrated waste disposal units.
Many new dishwashers feature microprocessor-controlled, sensor-assisted wash cycles that adjust the wash duration to the quantity of dirty dishes (sensed by changes in water temperature) or the amount of dirt in the rinse water (sensed chemically/optically). This can save water and energy if the user runs a partial load. In such dishwashers the electromechanical rotary switch often used to control the washing cycle is replaced by a microprocessor but most sensors and valves are still required to be present. However, pressure switches (some dishwashers use a pressure switch and flow meter) are not required in most microprocessor controlled dishwashers as they use the motor and sometimes a rotational position sensor to sense the resistance of water, when it senses there is no cavitation it knows it has the optimal amount of water. A bimetal switch or wax motor opens the detergent door during the wash cycle.
European dishwashers almost universally use two or three spray arms which are fed from the bottom and back wall of the dishwasher leaving both racks unimpeded and also such models tend to use inline water heaters, removing the need for exposed elements in the base of the machine that can melt plastic items near to them. Many North American dishwashers tend to use more basic, and old fashioned water distribution and exposed elements in the base of the dishwasher. Some North American machines use a large cone or similar structure in the bottom dish rack to prevent placement of dishes in the center of the rack. The dishwasher directs water from the bottom of the dishwasher up through this structure to the upper wash arm to spray water on the top dish rack. Some dishwashers, including many models from Whirlpool and Kitchenaid, use a tube attached to the top rack that connects to a water source at the back of the dishwasher which allows full use of the bottom rack. Late-model Frigidaire dishwashers shoot a jet of water from the top of the washer down into the upper wash arm, again allowing full use of the bottom rack (but requiring that a small funnel on the top rack be kept clear).
Some dishwashers include a child-lockout feature to prevent accidental starting or stopping of the wash cycle by children. A child lock can sometimes be included to prevent young children opening the door during a wash cycle. This prevents accidents with hot water and strong detergents used during the wash cycle.
A dishwasher should never be emptied before a complete process has been signified to be finished by the control system, as this will often leave the contents unwashed or still in a saturated state. It is a common misconception that to empty a dishwasher before the end of a cycle will save energy, as many of the contents may need to be re-run, hence almost doubling running costs.
Plumbing
Depending on the model, some dishwashers can be plumbed into either the hot or cold water supply, taking into account the maximum incoming water temperature recommended by the manufacturer where hot water is used. Plumbing a dishwasher into the hot or warm water supply can improve cleaning performance and reduce food debris in the interior of the dishwasher. A few dishwashers may spend much less time on the wash phase if the incoming water is hot, which can compromise cleaning, so results will vary. Dishwashers may cost less to operate on a hot water supply if there are other forms of energy available that allow water to be heated more cost efficiently than an electrically powered heating element in a dishwasher.