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How Does A Garbage Disposal Work: A Detailed Explanation

Garbage disposals are very popular in the USA but not so in most other countries. They were used in our homes since the 1930s and they never fell out of their popularity.

What is a garbage disposal?

I don’t think anyone in the USA doesn’t know what a garbage disposal is unless they lived their entire life in New York City, like AOC. These machines were banned in NYC until 97 over concerns for the aged sewer system. To those who do not know;

Garbage disposals are grinders that are installed under a kitchen sink to grind and dispose of food scraps. They are connected to the drain hole of the sink so that any food waste you put in the sink will reach the garbage disposal grinders.

Garbage disposal installed under a sink
Image of a garbage disposal installed under a kitchen sink

Garbage disposals run on electricity. They are available in different power ranges from 1/3 HP to 1 HP. There are also commercial garbage disposals that have up to 10 HP power ratings. Depending on their motor’s power garbage disposals consume 5 to 11 amps of electricity for a 120-volt power supply.

Garbage disposals are installed under the sink with the help of a mounting assembly. Depending on the brand of the garbage disposal you are buying, there are two types of such assemblies, they are; 3-bolt and EZ mount. Both these mounting assemblies use a sink flange and a twist and lock mechanism to secure the garbage disposal to the kitchen sink.

Working of garbage disposals explained

Most people believe that garbage disposals use sharp blades to cut food wastes, just like a blender. But that is far from true. Garbage disposals do not have blades. Instead, they use impellers and shredder rings.

A garbage disposal works by throwing food at a stationary shredder ring with the help of a fast rotating impeller. The shredder ring has sharp projections which break down the food into small sizes. It also has small holes in it through which the ground food wastes are washed away.

Let me explain this process in detail. A garbage disposal has 3 main parts; a motor, a grinding chamber, and inlet and outlets.

The inlet, aka mouth of the garbage disposal, is on its top. It is connected to the drain hole of the sink. Depending on the garbage disposal brand, the size of this inlet opening varies, but all of them can be mounted on a sink with a standard drain hole size of 3.5 to 4 inches.

The outlet of the garbage disposal is connected to a drain pipe. All garbage disposals come with a standard drain size of 1.5 inches.

The inlet of the disposal opens directly into its grinding chamber. The grinding chamber is a cylindrical chamber with a fast rotating impeller disc at its center and a stationary shredder ring around its walls. Two freely rotating metal lugs are attached to this circular impeller opposite each other. These lugs are blunt, not sharp. Some garbage disposal models also have impellers with some sharp projections in addition to these lugs to improve grinding.

Just beneath this grinding chamber, and totally sealed from it, is the motor. They can be a permanent magnet or induction-type motor. This motor is directly connected to the axis of the impeller via a metal rod. There is no speed control mechanism between the motor and the impeller, so the impeller runs at the same speed as the motor.

Here is how it works. When the garbage disposal is switched on, the motor rotates the impeller disc at high speeds. The speed can range from 1700 to 2800 RPM, depending on the disposal model. The freely rotating lugs on the rotor also rotate at this high speed hitting the food wastes like a hammer. This action breaks down large pieces of food into tiny pieces, and the hammering action also forces them against the shredder ring, which has some sharp points and tiny holes in them. Once the food wastes are tiny enough to pass through these holes, they escape into the drain pipes through the disposal outlet.

A video showing the working of a garbage disposal

How to properly run a garbage disposal

Now that you understand the inner workings of a garbage disposal, here is a simple guide to using them;

Step 1: Run plenty of cold water

It is important to run plenty of water even before turning on the garbage disposal. And the water has to be cold, not hot. This is because the food you put in the garbage disposal can have grease and oils in them, and they are a problem when in liquid form. When you run hot water, this fat and oils melt, and they solidify in the drain pipes, clogging them.

Running water is important to properly grind food wastes and remove them through the drain pipes. Without enough water, the garbage disposal can jam, and the food wastes can also clog the pipes. Running water prior to turning on the disposal also helps wash away any debris left in it and in the pipes.

Step 2: Turn on the garbage disposal and start adding food scraps

There are two types of garbage disposals based on how food wastes are fed to them; batch feed and continuous feed. If yours is a batch feed garbage disposal, it comes with a magnetic cover. This magnetic cover also acts as a switch without which the disposal won’t turn on. In this case, you have to fill up the disposal with food scraps and then turn it on. So here, you are grinding the food wastes in batches; you can’t add them while the disposal is running.

If yours is a continuous feed garbage disposal, it is turned on by flipping the switch. It doesn’t have any cover covering its mouth, so you add food wastes into the disposal while it is running. This means you can continuously empty one plate after another, and that is precisely why these garbage disposals are called continuous.

Irrespective of the type of garbage disposal you are having, you should run plenty of cold water throughout the grinding process. You should also do not force lots of food into the disposals; this leads to jams and clogs.

Also, please know that your garbage disposal cannot grind all sorts of food wastes. As a general rule, you shouldn’t add fibrous or tough food items. Here is a detailed list of what you shouldn’t put in a garbage disposal for your easy reference.

Step 3: Keep running them for a few seconds more

It is not advised to immediately turn off the disposal and water after the grinding is done. Let the garbage disposal run for around 10 more seconds with the water still running. This will help wash away anything that is left in the disposal’s chamber and also in the drain pipes.

Where does the waste go from a garbage disposal

The pulverized food wastes from a garbage disposal either go to the public sewage system or to a septic tank, depending on how your plumbing is done.

If the plumbing is connected to a sewage system, the food wastes will sit in water and ultimately reaches a water treatment system. Depending on the water treatment system, these food wastes can be turned into fertilizer or a source of energy. Some treatment plants also dump them in landfills.

If you have a septic tank, the food wastes will be broken down by the bacteria in the system.

How to maintain a garbage disposal

A garbage disposal can run for around 15 years if you take good care of it. These machines seldom need any heavy maintenance, using them properly will increase their life expectancy. Doing a few things can achieve this.

Add only disposal friendly food wastes: As mentioned before, there are many food items you shouldn’t put in a sink disposal. Adding them can cause jams and clogs, ultimately leading to more problems.

Do not use harsh chemicals: Harsh chemicals can corrode the components of a garbage disposal leading to leaks. You cannot repair a leaking garbage disposal, it should be replaced. So the use of cleaning chemicals can lead to costly problems. There are much easier easy to clean them: check this article.

Clean it once a week: Even if you use it properly, spend a few minutes cleaning them each week. Regular cleaning can reduce rust buildup and eliminate smells.

My name is Thomas Anderson, author of DisposalQA. I have 15 years experience working as a plumber in CA, and this is where I answer common questions about garbage disposals.