The Washing Machine Man

Appliance Specialist.

Tony's tips for understanding your dishwasher......

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Modern dishwashers save water. They use as little as thirteen to fifteen litres of water to wash  dishes for twelve or so people. Try doing that in the kitchen sink. You would have pea soup in the sink in the end.The older models were quite basic. Technology has come to the fore. Older models used up to thirty litres of water and were very noisy. Not the case now.

  • How does the modern dishwasher work?  Because of such little water per fill, measurement of the amount of water in the tank is quite sensitive. Once,with larger amounts of water , measurement was by way of a pressure operated switch. Now there are other methods used.   The first is using time fill. The control of the appliance is set to accept water during a time frame. The water valves are traditionally about four litre per minute valves so the time frame is built around that flow rate. This time frame can be changed to suit differences in water pressure. This method has a disadvantage of not always filling to the same level, as water pressure variations alter the flow rate into the machine.  A more reliable method is to use a reed switch and water wheel. Water flows through a tube and turns a paddle wheel. This wheel operates a tiny 'switch' as it turns. The controlling computer in the appliance  counts the number of revolutions of the wheel, and when the correct number is reached the cycle is triggered.. This method allows for faster or slower flow rates and automatically compensates for variations. It is a more reliable and accurate way of measuring water level. Another is an air lock system where water rises in a filler box consisting of chambers and eventually operates either a float micro switch or a pressure diaphragm switch.The water wheel method is the one used by most of the makers of quality machines.
  • Loading and setting.Dishes should be stacked appropriately in the racks without coming into contact with each other. Scrape food off of the plates first. This is a dishwasher not a garbage disposer. Most top end machines have a 'turbidity sensor'. (I guess its about minimizing user intervention; making it as easy as can be). This device is like a camera that takes a picture of the water after the wash has started. This 'picture' tells the controlling computer how dirty the water is, and so the cycle can be automatically adjusted according to how dirty the dishes are. The base temperature of some turbidity sensor cycles  is fifty degrees. This ensures that no matter what, there will be a temperature of fifty degrees reached. If the dishes are really dirty then of courrse the temperature will be higher; up to sixty five or even seventy degrees. Some makes are fourty five degrees on the base temp which is a bit on the cool side in my book. The turbidity sensor requires some grease on the dishes to enable it to work properly. The makers therefore recommend that you just scrape your plates and let the dishwasher do the rest. Leave grease on the dishes they say. Some people, like me, prefer to keep more grease and fat out of the appliance. The less 'muck' that passes through the wash pump and the drain pump the better, and the less smelly your appliance becomes.  So if you rinse your dishes first, and use the 'AUTO' cycle, the computer won't allow much heat and time,as the picture taken of the water will show no dirt, so the wash quality will be poor.i.e. low heat and short wash. Someone who prefers to rinse the dishes and keep the 'muck' away from the works of the machine and to have the machine smelling nicer after a day or so of not using the machine,might consider what I do, and use a fixed cycle, say at least sixty degrees and not 'AUTO'. By the way, rinsing the dishes first does use a little more water, but even if you added five more litres to allow for this, the consumption is still below twenty litres. I have a machine with a turbidity sensor and choose to use a fixed cycle over sixty degrees. Heat and hygiene go hand in hand. A point to note.Some normal cycles are calibrated to give the best energy rating.The energy rating assists the sale as there are more 'STARS' on the ticket. Beware of the use of these NORMAL cycles. Sometimes there is insufficient heat and cycle time to do the job properly. You may need to choose a cycle other than normal for best results.  Ask Tony
  • Using product and washing. Tablets are very popular. I guess it's all about making everything too easy. Just chuck a tablet in and that's it. No powder to put in the dispenser and no rinse aid to top up. That's good on the surface, but look what can happen. The maker of the appliance has gone to the trouble of making a dispenser to allow detergent to enter the dishwasher at 'just the right time'. Usually about when the heating of the water begins. This is done for a definite purpose. Tablets  placed in an open dispenser begin to dissolve immediately the water begins to cycle, not when the best effect is obtained. Dishes placed inside the machine should be rinsed first with cold water and no soap. Certain greases respond to cold water .When the right time occurs the product dispenser opens; about when  the machine begins to heat. The powder dissolves rapidly and makes a solution to wash the dishes. This has been 'timed' by the maker of the machine. Also the rinse aid is dispensed at just the right time. When the hot rinse occurs. Rinse aid dispensers should be set to about two or three. If you get streaks on your glasses, lower the setting by one and try. If you get water stains increase the setting by one and try. Rinse aid 'wets' the dishes to allows water to 'slide' off of the dishes and so improves drying and removes water marks. The solvency rate of tablets doesn't suit all machines with different cycle times. Tablets can dissolve before the rinse aid component is required, or take longer to form a wash solution. Also from experience, some tablets 'attack' the plastic coating on the racks and shorten the life of them. Tablets can tend to 'foam' in  some machines and cause the wash pumps to surge.( More froth than water.)This can effect the operation of the heater pressure switch in the wash pump and cause it to fail. At the worst this foaming can also cause the electronic control unit to fail because of the rapid switching of the heater pressure switch.  Why not go along with the way the machine was intended to be used? Use powder in the appropriate compartment and rinse aid in its' compartment.  Ask Tony.
  • Why then would the makers of some machines provide tablets as a sample in their new machines. Aren't they encouraging the use of tablets, contrary to what you have just read? Ask Tony.
  • Some machines alternate the water flow between the top and bottom arms providing more intensity to each rack alternatively. There is a motor driven valve to achieve this.
  • Drying. ,Older models with immersion heaters inside the tank heated the machine full of dishes at the end of the cycle. The tank being vented allowed the moist hot air to escape and the heat dried the dishes. Now dishwashing machines don't have heating elements inside the tank. Nothing to melt plastic items that fall onto the element. Heaters are mounted in various places, either at the side or underneath the tank. These are  flow through heaters.Heat pumps are used too, where the water is heated in the wash pump. So the method of drying has changed. Condensing action is the method  used. The principle is to have a differentiation of heat between the dishes inside the appliance and the tank wall. The moist air is attracted to the colder tank wall and the moisture runs down the inner wall of the tank and runs into the sump to be pumped to the drain. Different methods are used to enhance the condenser action. Latent heat method is to simply rely on the heat inside the tank from the final rinse to dry the dishes.As the tank cools it condenses the water to the sides. A better more efficient  method is to run cold water down the back or side  of the tank and so set up a better condensing action.Some machines do this. Others have a fan that blows the colder atmospheric air along one side of the tank to enhance condensation. A really good method is to use a heat exchanger. This consists of a thin plastic tank mounted to the side of the dishwasher, between the stainless steel tank and the outside panel. The heat exchanger has two functions. It fills with water at the beginning of the cycle and the water is warmed up in it by the hot water in the tank during the wash cycle. During the rinse the water in the heat exchanger is used , and being already warm the dishwasher doesn't have to heat it from cold so giving the rinse cycle a 'head start' and shortening the cycle. At the end of the cycle the heat exchange box fills with cold water, and being up against the tank, the cold water in this heat exchanger cools the tank and causes the condensation to occur. Opening the door slightly at the end of the drying cycle really does improve drying. This requires user intervention and could be inconvenient, but it works.A couple of  top end makes have  a feature where the door is opened automatically by a push rod slightly at the end of the cycle at the appropriate time.
  • A point of interest here is to consider the ambient temperature. Condenser action requires a temperature difference between the tank and the dishes. If the cycle used is, say 45 degrees or even 50 degrees, and the ambient temperature is say 30 degrees, the condenser action won't work as well as if the cycle used was say 65 degrees and the ambient temperature is 30 degrees. This means the dishwasher dries better on a cold day using a 65 degree cycle.
  • Cycle times of new dishwashers are much longer than the older models. This is because of the lower water usage. The principle is, less water but more time to produce a clean result. Also the wash motors run slower for longer to use less power overall. There are choices on some models where a TURBO cycle can be selected to allow the motor to run faster with more vigorous washing to shorten the cycle time.
  • General tips. Check under the lower door seal along the bottom of the door regularly. Much grease and fat can build up here and must be cleaned away. Use a brush with a handle as there could be some sharp edges to cause cuts. Wipe around the tank seal and around the door . Take notice of the hinge area where grease can accumulate. The filters in the sump must be kept clean. Make sure they fit properly and remain 'clipped in place' as food particles can cause problems it too much gets past the filters. Stones and seeds are the worst.The spray arms must not have any blockages in the jets. Remove the arms and clean them out. Be diligent with your appliance, it is designed to work for you but it doesn't like being misused. A proud owner will have a hygenic and sweet smelling appliance, and will get the most out of it. They cost too much to be careless, don't they? Machines don't need descaling very often. If you use them properly,they clean themselves. Ask Tony

┬ęTony Pike 1/1/2010

A fully stacked dishwasher

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