How Dishwashers Work

By: Ed Grabianowski & Melanie Radzicki McManus  | 

child stacking dishwasher
Dishwashers have become a staple in just about every kitchen. Thanasis Zovoilis/Getty Images

Basically, a dishwasher is a robot that cleans and rinses dirty dishes. Humans have to load the dishes, add detergent, set the proper washing cycles and turn it on, but the dishwasher accomplishes a whole series of functions by itself. A dishwasher:

  • Adds water
  • Heats the water to the appropriate temperature
  • Automatically opens the detergent dispenser at the right time
  • Shoots the water through spray arms to get the dishes clean
  • Drains the dirty water
  • Sprays more water on the dishes to rinse them
  • Drains itself again
  • Heats the air to dry the dishes off, if the user has selected that setting

In addition, dishwashers monitor themselves to make sure everything is running properly. A timer (or a small computer) regulates the length of each cycle. A sensor detects the water and air temperature to prevent the dishwasher from overheating or damaging your dishes. Another sensor can tell if the water level gets too high and activates the draining function to keep the dishwasher from overflowing. Some dishwashers even have sensors that can detect the dirtiness of the water coming off the dishes. When the water is clear enough, the dishwasher knows the dishes are clean.

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Although dishwashers are watertight, they don't actually fill with water. Just a small basin at the bottom fills up. There, heating elements heat the water up to as much as 155 degrees Fahrenheit (68 Celsius) while mixing in the detergent. Then a pump propels the water up to the spray arms, where it is forced out and sprayed against the dirty dishes.

Think about a garden hose with no nozzle — if you put your thumb over the end of the hose, decreasing the space for the water to come out, it sprays out more forcefully. The dishwasher's jets work on the same principle. The force of the water also makes the spray arms rotate, just like a lawn sprinkler.

Once the food particles are washed off of the dishes, they are either caught in a filter or chopped up into small pieces and disintegrated, similar to the actions of a garbage disposal. Then the cycle of heating water, spraying it and letting it drip back into the pool below repeats several times.

When the washing and rinsing is finished, the water drains down to the basin again, where the pump propels the water out of the dishwasher. Depending on the type of dishwasher, the drained water might go right into the pipes under your sink or into your garbage disposal.

The final step in a wash cycle is optional — the dry cycle. The heating element at the bottom of the dishwasher heats the air inside to help the dishes dry. Some people just let them dry without heat to save energy.

Dishwashers are not very mechanically complex. In the next section, we'll take a look at the main parts of a basic dishwasher.

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Dishwasher Basics

dishwasher illustration
Dishwashers have become a staple in just about every kitchen. Shutterstock/HowStuffWorks

Here are the main parts of a dishwasher:

Control Mechanism

The control mechanism is located inside the door behind the control panel. Many units use a simple electro-mechanical system: a timer determines how long each part of the cycle lasts and activates the proper function at the proper time (such as the detergent dispenser, wash spray and draining functions). Units that are more expensive might have a computerized control system. Modern units also have a door latch that must be closed for the unit to run. Some also have child safety locks.

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Water Intake Valve

This is where water from the home's water supply enters the dishwasher. Mounted on the inside of the dishwasher, the valve opens and closes to let in the proper amount of water during a cycle. When the valve opens, water pressure drives the water into the unit.

Circulation Pump

An electric motor powers the circulation pump. During the washing cycle, the pump forces water up into the spray arms. During the drain cycle, the pump directs the water into the drain hose. The pump assembly is mounted beneath the basin, in the center of the dishwasher. There are two main types of pumps:

  • Reversible. These pumps switch between pumping water to the spray arms and pumping water to the drain by reversing the direction of the motor. Reversible pumps are usually vertically mounted.
  • Direct-drive. In these pumps, the motor only runs in one direction. So, the direction of the water flow switches from the spray arms to the drain pipe via a solenoid valve. Direct-drive pumps are usually horizontally mounted.

Dishwashers can be installed in either a portable or permanent configuration. Portable units have finished sides and a top that can be used as a countertop. When not in use, the machine sits in place next to the wall. When it's time to run a cycle, the unit can be rolled on casters over to the sink, where it connects to the faucet and plugs into a nearby outlet.

In a permanent installation, the dishwasher goes underneath the existing countertop and bolts into place. Hoses underneath the kitchen sink connect directly to the hot water line and the drain line, and the unit usually plugs in under the sink as well. Both types of installation require a 120-volt grounded line.

Next, we'll look at how to use a dishwasher.

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Using a Dishwasher

a fully stacked dishwasher
Don't overfill your dishwasher. Jaap2/Getty Images

Even though the dishwasher does most of the work, humans play a part, too. Here are some guidelines that can help your dishwasher operate safely, effectively and efficiently.

  • Don't use regular dish soap. The suds will overflow the dishwasher.
  • Don't overload the dishwasher. You need to leave room for the water jets to spray onto the dishes.
  • Face the dirtiest part of the dishes toward the spray jets, which usually come from the center.
  • Don't mix stainless steel and sterling silver (or silver plate) items. Putting two different types of metal in contact in a humid environment is a perfect recipe for corrosion or pitting.
  • Try to keep bowls, spoons and other dishes with identical shapes separated. Otherwise, they will tend to nest together, and the water cannot reach every part of the dish.
  • Don't put wood, cast iron, fine china, crystal or hand-painted dishes into the dishwasher. Wash these items by hand.
  • Use the dishwasher at a time of day when water pressure is high, such as late at night. The dishwasher will clean better if you're not using a lot of water for something else, like washing clothes.
  • If your home has hard water, use slightly more detergent.
  • Use a rinse aid to avoid spots and help your dishes dry more quickly.
  • Don't put plastics on the bottom rack, especially if you use the hot drying cycle. The heating element could melt some plastics.
  • Don't pre-clean dishes. Dishwashers actually depend on the bits of food that cling to dirty dishes to maintain an appropriate pH level inside the dishwasher. Large pieces should be scraped into the garbage, though.

Detergent

Detergent is an important consideration when running a dishwasher. Detergents counteract mineral deposits, or hardness, in the water. They contain solvents that help dissolve food, have abrasives that scour away stuck-on gunk and help food slide off dishes more easily.

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You can't use just any detergent in a dishwasher; only detergents specially formulated for dishwashing machines will work. Other detergents could damage dishes or generate so many suds that the dishwasher would overflow. Which detergent to choose — tablet, powder or gel — is really based on personal preference. One type hasn't been shown to clean better than another type. Just make sure the detergent is fresh — less than two months old — or it won't clean as well.

Troubleshooting

The problem most people encounter with dishwashers is a simple inability to get the dishes clean. There might be stuck-on food or residue from the detergent. A water pressure problem may be the culprit. You may need to replace the water intake valve. Another common problem is mineral build-up. If your house has hard water, the mineral build-up can clog the water jets. Clear each jet with a wire or pin and run an empty load with some vinegar in the detergent dispenser once a month.

Sometimes, a dishwasher has problems draining properly. There could be a clog in the drain hose or a problem with the pump. It's also possible that the dishwater is getting too sudsy, and sensors in the washer aren't detecting the soap foam as water. This causes it to shut down the drain cycle too early. Just use less detergent.

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Dishwasher Buyer's Guide

Smart dishwasher/ tablet
Smart dishwashers allow you to start them from your tablet. izusek/Getty Images

Modern dishwashers all function in the same basic way. Even cheaper models do a good job of cleaning dishes. That makes buying one a matter of finding features you'll use and avoiding ones you don't need. Durability, size and convenience are the primary factors that set one model apart from another.

Size

A standard 24-inch dishwasher
A standard 24-inch dishwasher
Photo courtesy of Consumer Guide Products

Dishwashers come in a wide variety of sizes. The smallest are countertop and in-sink dishwashers, which can wash up to six place-settings. Countertop units don't require installation, as they sit on top of your counter. In-sink dishwashers typically fit into one-half of a double kitchen sink and can wash a complete load in about 20 minutes. When not in use, a cover on the unit lets it serve as a countertop.

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The standard size for a dishwasher is 24 inches (61 centimeters) wide. However, 18-inch (46-centimeter) units are available, sometimes known as "apartment-sized" dishwashers. Obviously, the wider the dishwasher, the more dishes it can hold. If you have a large family, a 30-inch (76-meter) model might be the right size. Any larger than that, and you're probably looking at a commercial dishwasher.

A more unique offering is the dish drawer, a small dishwasher the size of a large kitchen drawer. It uses less water and energy than a full-sized dishwasher uses and is suited for small kitchens that don't have enough room for a full-size unit. However, they also come in double-drawer models that can hold as many dishes as a standard dishwasher. These drawers function independently and, in addition to their water and energy economy, are perfect in kitchens where a dishwasher door would block a walkway.

Basins and Racks

Lower-end dishwasher models have plastic basins, while some mid- and all high-priced units have stainless steel basins. In cheaper models, bits of food settle into a filter that must be manually cleaned on a regular basis. Models that are more expensive have self-cleaning filters, and some include small grinders that grind up large chunks so they drain with the dirty water.

Dish racks come in many configurations. The more you pay for the dishwasher, the more flexibility and adjustability you'll get, with collapsible racks, folding tines, extra shelves, and removable racks for loading outside the machine. If you have large or oddly shaped dishes that you'll be washing regularly, take them to the appliance store to make sure they'll fit the racks.

Extra Features

Today's appliances are growing ever smarter and more energy efficient, with past upgrades now standard on even the least-expensive models. One example: Most dishwashers now feature a soil sensor that saves water by sensing how dirty your dishes are and adjusting the wash time and water amount accordingly. Other energy-saving options include half-load and speed-wash cycles.

More expensive models boast WiFi connectivity, allowing you to control your appliance from your smartphone. You can not only start your dishwasher remotely, but also check the remaining cycle time, lock the buttons (should younger kids be at home), and receive alerts when your rinse aid is low or there's a possible leak. You can even program your dishwasher to run only when local energy consumption is low, which may save you money. Other newer features include a slim, third rack for large, flat items; bottle jets to better clean baby bottles and water bottles; and racks you can move both up and down.

Expensive dishwashers can be stylish, with fronts designed to look like kitchen cabinets. Noise suppression might be worth the extra cost if your kitchen is close to your living room. Dishwashers that are more expensive have heavy insulation against noise. Note that dishwashers with grinders for large food chunks are louder than those without them.

Energy Use and Cost

One final consideration is water and energy use. The U.S. government's Energy Star program lists the most efficient dishwashers each year to help you select a model that's best for the environment and your pocketbook.

So how much can you expect to pay for a modern dishwasher? In 2021, you could snag a reliable, functional model for less than $600. If you could afford to shell out $1,000, that would get you features like a third rack, a quieter machine and a powerful food disposal. Prices go all the way to $2,000 and more for dishwashers with every possible feature, including WiFi connectivity, additional cycles, hidden controls, LED lights, built-in water softeners and water cleanliness sensors.

Government regulations have greatly improved the efficiency of modern dishwashers, so unless your dishwasher is a pre-1990 model, it's probably efficient. ENERGY STAR certified dishwashers are 12 percent more energy-efficient and 30 percent more water-efficient than standard models, according to the Environmental Protection Agency. A standard-size ENERGY STAR certified dishwasher costs about $35 annually to run and will save about 3,870 gallons (17,593 liters) of water over its lifetime.

Using a dishwasher saves time, but it even saves energy and water compared to washing dishes by hand. How much? An Energy Star dishwasher saves an amazing 7,000 gallons (26,500 liters) of water annually, compared to washing dishes by hand. It also gifts you with an extra 230 hours of time and shaves $111 off your utility bills.

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Originally Published: Mar 28, 2006

Dishwasher FAQ

Is a dishwasher worth buying?
Because of their efficiency, in terms of cost and energy usage, dishwashers are worth buying. They're a must-have for large families and office spaces. If you don't have as many people in your house, you may be interested in a double drawer dishwasher instead.
How do I choose a dishwasher?
A good dishwasher should have a high unit capacity to handle many dishes and large dishware. You should also look for specialty wash cycles such as "rinse and hold," "quick wash," "sanitize," and "delicate." Finally, you should look at the energy usage of the appliance.
How do portable dishwashers drain?
You can drain portable dishwashers with a tool known as a ‘unicouple' that can be outfitted to a kitchen faucet. The unicouple has two hoses, one for the dishwasher and the other for the sink.
Do portable dishwashers work as well as built-in dishwashers?
Portable dishwashers can clean more efficiently for smaller households. However, the unit capacity for portable dishwashers is lower than built-in dishwashers and there are clear limitations. They may be a good choice for families who are renting their home.

Lots More Information

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More Great Links

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