How a dishwasher works

A dishwasher is the most mysterious domestic appliance. You shut the door, turn it on, hear the sounds of sloshing water, and the dishes appear clean. I had assumed that it was something like a clothes washing machine in that it filled the container with water and then churned it around. But I noticed that our new dishwasher seemed to go into the sloshing sound mode pretty quickly, long before there would be time to fill the volume. So I was glad to come across this video where someone had placed a camera inside the dishwasher to reveal its secrets.

My dishwasher does not seem to have the central spout. Instead it has a blade at the bottom with holes in it and I suspect that it achieves the same result by the blade spinning in the horizontal plane while squirting water upwards.

One consequence of this new knowledge is that my fear of accidentally opening the door and flooding the kitchen is gone. It looks like the water would shut off immediately with only a slight splashing.


  1. moarscienceplz says

    My dishwasher does not seem to have the central spout.

    Are you sure? A heavily-loaded dishwasher would block most of the water jets trying to squirt all the way from the bottom of the chamber up to the underside of the dishes in the upper rack. A large bottom blade is pretty much standard in all dishwashers, but a central spray source is generally needed as well. Plus, it probably also has a spinning arm mounted on the “ceiling” of the dishwasher as well.

  2. colnago80 says

    I have a flash for the good professor. The newer clothes washing machines don’t fill up with water either. They are computer programmed to detect the amount of clothes in the washer and use only the minimum amount of water needed. They also use special low suds soap and a lot less of it then older machines. They also have a spin cycle that allows your dryer to dry the clothes in less time then was required with older model machines. All in all, saves on both soap residue in the sewers, uses less water, and allows shorter drying times in the dryer, thus saving energy.

  3. says

    If the door open detector fails on your dishwasher, you can have an exciting time if you open it while it’s in full-up hot rinse.

    Also, don’t ever use detergent that is not designed for a dishwasher. The amount of surfactant is critical and if you use industrial surfactants your dishwasher will become a solid block of foam and the pumps may melt. Uhhhhh, I am not sure I want to talk about how I learned that one.

  4. says

    Re: #2 -- Yes, and modern clothes washers pretty much eliminate the need for a hot wash or hot rinse — cold/cold will almost always do fine unless you’re trying to kill fleas or bedbugs or something like that (which won’t work anyway)

  5. Mano Singham says


    I looked again and there is nothing at the bottom but there is another rotating blade just below the top rack and what looks like it may be a spout that comes down from the very top. So that may be the central spray source you mention.

  6. Conner Bias says

    Thanks. This is why I have the internet. I wonder if anyone has ever flushed a GoPro down a toilet, perhaps on a string, so that it could be rescued?

  7. Crip Dyke, Right Reverend Feminist FuckToy of Death & Her Handmaiden says

    I was sooooooo ready for a post on the working conditions of bussers and other low-paid restaurant workers.

    I had a bwuh?

    But done now. This is good too. Machines are interesting. And our dishwasher is broken. My honey is trying her hand at diagnosing, part-ordering, and fixing. I hope she succeeds.

  8. Trebuchet says

    How my dishwasher works (in this location):
    1. Collect the dishes to be washed.
    2. Place dishpan in sink. Put flatware in it.
    3. Add liquid detergent.
    4. Add hot water
    5. Wash flatware.
    6. Rinse flatware.
    7. Dry flatware.
    8. Wash, rinse, and dry other stuff. (Not too much. We use a LOT of paper plates.)
    9. Say “Phew, I’m done for a couple of days.”

    @Mano: Your dishwasher may well have a telescoping tube in the center of that bottom spraybar which pops up to provide water to the upper spraybar. It’s pretty common.

  9. lorn says

    This guy spent hundreds of dollars to figure out how a dishwasher worked. For half that I would have told him how I run a little warm water, squirt a bit of Dawn, use a brush to get the rough stuff, rinse, and stack in rack.

    As far as clothes go, for getting rid of fleas, lice and other pests, your best tool is the drier. A couple of minutes on hot, get the temperature over 150F for a minute and the wee critters die. If you don’t wash the clothes first the clothes don’t have any water to slow down the heating process so they heat up very evenly and rapidly. If you wash first the seams and waistbands are wet and defy heating so the critters can hide in them and survive longer so you have to work them in the drier much longer. I learned this from a public health nurse with a lot of experience fighting lice in schools.

  10. hyphenman says


    My grandfather, in one of his many incarnations, owned an appliance store (what used to be called a brown and white goods store) and did his own repairs. We had an early dishwasher that fascinated me and he took the time to teach me exactly how it worked.

    The bit that I found most interesting was how the dishwater recirculated the water and used an internal heater to keep the water at the desired temperature so that the actual amount of water (and energy needed to heat the water) was less than that used by the more traditional wash-and-rinse in the sink method.

    From an ecological standpoint, the process is easier on the environment than the alternative as long as you’re careful to only do large/full loads.


  11. colnago80 says

    Re Marcus Ranum @ #5

    Good point. Also, clothes last longer when cold water is used.

  12. Jockaira says

    Clothes also last longer if you don’t subject them to high heats in a clothes dryer. Putting them on a clothesline to dry in the air works fine, uses no electricity or gas, generates no lint in a filter, and gives the dried clothes a nice fresh smell.

  13. colnago80 says

    Re Jockaira @ #15

    I don’t know where you live but in most of the US, putting clothes on a clothesline outside during the winter months is not a good idea. Putting the dryer setting on delicate fabrics (equivalent to medium heat) will also lead to longer life for them.

  14. says

    On a sunny day, when my solar panels are producing enough juice for it, I run a 60 degree wash. I figure if I’m not adding any CO2 to the atmosphere anyway, then I might as well try to get away with using less detergent (which is probably doing damage of its own anyway).

  15. Mano Singham says


    We have a line and drying racks in the same room as the furnace and in winter that room is so warm and has such low humidity that clothes dry almost in a flash.

  16. thebookofdave says

    You can tell this was filmed on some kind of set or mock-up, instead of an actual dishwasher. The viewpoint if from one of the corners, providing no room at all for a camera operator. In related news, I can tell you from experience that the light goes off when the refrigerator door is closed (due to my fear of the dark, probably won’t repeat that trial anytime soon).

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