HOW THE DISHWASHER WORKS by David Lawyer, Aug. 1995 If you would like step-by-step instructions, please see another document. But if you expect to operate the dishwasher more than just a few times, you should understand how it works so that you can get the most efficient use out of it and solve any problems that may arise. This is an old commercial dishwasher made in the 1960's but it's by no means obsolete since newer models are not all that much better. Such a dishwasher costs several thousand dollars and parts for it are very expensive so be careful not to damage it. It will wash and rinse a rack of dishes in 60 seconds (1 minute). It washes for 50 seconds and rinses for 10 seconds. To wash a rack of dirty dishes, all one needs to do is push the rack into the dishwasher, lower the door with the handle (a horizontal round bar) and the rest is automatic. After a minute, the door pops up exposing a clean rack of dishes. You may now push in another rack of dirty dishes and repeat the process. However, before one starts doing the above, the tank at the bottom of the dishwasher must be fill of water. There is a water level sensor that detects this. Hopefully the water is hot and contains detergent, but the dishwasher will operate even if the water is cold and/or contains no detergent. The dishes are washed by a fast stream of washwater pumped from the tank into the 2 large rotating metal wash arms. One is above the rack and another below. The washwater hits the dishes, removes food stuck to them, and drains by gravity back into the tank to be used over again (recycled). This water passes thru the 4 filter trays located above the tank to remove larger chunks of food. These trays can be easily removed and cleaned with water. The dishes are automatically rinsed for 10 seconds by spraying fresh water on them. Just above the bottom wash arm is a small rotating rinse spray arm. The rinse sprayers on the top are stationary. The rinse water comes directly from a "dedicated" hot water pipe which is fed from the water heater in the basement. There is no rinse-water heater, but insulation has been installed on this hot water pipe under the kitchen floor to keep the water hotter. The hot water supplied to various faucets should be cooler because: 1. It is mixed with cold water in the basement. 2. Their pipes have no insulation. During the rinse, the rinsewater drains off the dishes and flows into the washwater tank. This dilutes the dirty washwater with fresh rinsewater. The excess washwater flows into an overflow pipe and goes down the drain. This dilution does 2 things: 1. It makes the washwater a little cleaner by adding fresh water to it. 2. It deprives the washwater of detergent. However, when the dishes are being rinsed, a small amount of freshwater flows into the plastic yellow "detergent" tank on the wall. This results in water from this tank (hopefully highly saturated with detergent) overflowing into the washwater tank. This adds detergent to the washwater every time the dishes are rinsed and hopefully compensates for the loss by dilution as mentioned above. Now if you think about it, you may be able to guess a simple way for the dishwasher to fill the washwater tank with water. Just start the rinse cycle and let it run for much longer than 10 seconds. This is exactly what the dishwasher does automatically when you first turn it on (by setting the switch to "auto" and lowering the door. This sprays rinsewater which drains into the tank and fills it. Also, detergent gets into the tank as per above. But the washwater tank has a manual drain at the bottom. If it's open, the tank will never fill with water. Some people forget to close it, use up all the hot water in the basement water heater, and then someone complains that there is no hot water. The washwater tank contains electric heating coils which keep the washwater hot. The red temperature knob controls the temperature. A tiny light above this knob lights when the heating coils are heating. When you first turn on the heat, you often need to push the red reset button to get this light (and the heat) to come on. Unfortunately, the electric heater will stay on even if there is no water in the tank. To prevent it from burning out, don't forget to turn it off before draining out the water from the tank. On the top of the dishwasher are two temperature gauges showing the temperature of the wash water in the tank and the rinsewater in the pipe from the basement. The rinsewater cools down when the dishwasher is not operating but the washwater stays hot as long as the built-in heater is on. Also on top is a green bottle with rinse liquid. This is injected into the rinse water and allegedly causes droplets of water to drain off the dishes so that they don't need to be dried by hand. If the color isn't very green anymore, it's time to replace it. See another sheet for instructions. 1 2