The first reliable hand-powered dishwasher was invented in 1887 by Josephine Cochrane (US) and unveiled at the 1893 Chicago World’s Fair.
The Cochrane’s had a busy social life, and in 1870 when they moved into a large home, ideal for entertaining, they regularly entertained guests using heirloom fine china. After one event, when servants carelessly chipped some delicate dishes whilst washing up, Mrs. Cochrane was furious and refused to allow the servants to handle the china again.
The result was that, after every subsequent dinner party, she begrudgingly endured dishpan hands wondering why someone had not invented a machine that could clean dirty dishes, when machines had already been invented to sew clothes and cut grass. Consumed by the challenge of inventing an automatic dish washer, she developed the idea of securing the dishes in a rack whilst applying high pressure water to clean them.
Her husband William Cochran, who was a rising star in the Democratic Party, died in 1883 leaving a significant amount of debt, so the development of the dishwasher escalated from a project of convenience to a project for survival. Her first creation had wire compartments for plates, cups and saucers which were put inside a wheel that lay flat inside a copper boiler. A motor turned the wheel, pumping hot soapy water from the bottom of the boiler over the dishes, but it didn’t really work too well, so she got help with the design from mechanic George Butters, and the first patent on the refined design of the Garis-Cochran Dish-Washing Machine was issued on 28th December, 1886.
It was much later, in 1924, when William Howard Livens (UK) invented a small dishwasher that was actually suitable for domestic use. This was the first modern dishwasher, and incorporated most of the design elements that feature in the models of today – a front door for loading, a wire rack to hold the dirty crockery and a rotating sprayer. Drying elements were added to his design in 1940. It was the first machine suitable for domestic use, and it came at a time when permanent plumbing and running water was becoming increasingly common in residential properties.
Although there have been many improvements in design and components over the years, the basic functions of a dishwasher are essentially the same as before. A dish or glass washer is simply a machine designed to clean and disinfect plates, cups, glasses, cutlery, utensils, and trays by spraying a detergent solution to clean and a rinse additive to aid drying. By rinsing at high temperature (71*C for 7 seconds), items are also disinfected, so a commercial ware washing machine is now a time-saving necessity and valued capital asset for any commercial food and beverage operation.
Although large commercial dish washers look daunting and complex, they can be regarded simply as large stainless steel boxes that can wash and rinse items in water that is hotter than can be used safely by hand.
When a dish washing machine is first switched on, a solenoid valve (an electrically operated tap) is opened to allow fresh mains water to flow into the “Wash Tank” where electric elements heat the water to between 55ºC – 65ºC. As the wash tank is filling, an initial charge (amount) of chemical detergent is dosed at the appropriate level. We will look at the subject of chemical dosing in a later post within this series.
The initial charge is the amount of detergent that is added to the water in the wash tank to achieve a detergent concentration that will clean effectively at optimum levels. The detergent is dosed by a small electric pump and the amount dosed is programmed depending on the site water conditions and other factors (see later post on the impacts of hard water and lime-scale on wash performance). Once the correct amount of water and detergent is in the tank, and the rack of soiled dishes has been placed into the machine, the washing process begins.
In the wash process, the hot detergent/water solution is pumped from the wash tank through washing arms, fitted with spray nozzles, mounted above and below the racks of dishes. The pressure of the water jets causes the wash arms to rotate and disperse the spray on to the items being cleaned. In a well-maintained machine, the pressure of the spray is high and the mechanical action of the water striking the soiled surfaces, combined with the chemical action from the detergent, allows effective cleaning. The soiling is either completely emulsified by the hot detergent solution or flushed from the surfaces to be collected on scrap trays situated within the machine for later removal.
When the washing stage is complete, the items in the dishwasher are rinsed with clean, hot water. During the rinse cycle a specialised chemical called a rinse aid is dosed into a small boiler in the dishwasher that heats the water to 820C – 880C and the hot solution is sprayed onto the items in the racks to flush away any detergent residues and to assist streak free drying.
The chemical rinse aid simply speeds up the drying of the items by allowing the hot water to be shed from the surface efficiently without runs or water marks. In later posts we will examine the importance of consistent temperatures and the removal of lime scale in achieving maximum cleaning results.
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