Dishwashers, an overview of Commercial and Domestic Machines

Dishwashers an Overview

There are a range of different dishwashers on the market to cover the whole gamut of wash problems, from the small table top domestic machine, to the large conveyor machines which can wash and dry thousands of dishes per hour.

The dishwashing machine is also adapted to wash many things other than crockery, such as Printed Circuit boards in the electronics industry, laboratory glassware, Surgical Instruments, Butchers knives, specialist footware used in hospitals and clean environments.

There are even large machines which use the same technology to wash Hospital beds and equipment that you could stand up in, you name it if it can be washed there is a machine that can do it.

They all use the same four factors of the cleaning process Mechanical Action, Time, Temperature and Chemical action. Mainly using Hot water jets with detergent, these can be fixed jets or rotary moving jets so that all parts of the cabinet are reached by the water jets.

The Sinners diagram the four factors of the cleaning process

All cleaning processes depend on the same four factors, Mechanical Action, Time, Temperature, and Chemical Action.

For this reason it is important to understand that the design of the dishwasher for a particular project may require three phase power at 10/25kw with high pressure water supply and bags of space, down to a small machine in a restaurant with single phase 3/6kw power with cold water fill.

First we have to know the size of the task and the amount of space and money available to complete the project.

For a recap on how the wash process works click on the link to the laundry page which explains in detail why we use the sinners diagram for the purpose.

Because hardwater is a huge problem where heated water is concerned with hidden high power heating elements water should go through a water softener, Check out the Hardwater page now. This page will explain all the problems with lime scale build up and the solutions.

Or go to my page for all the insider knowledge on how the Go to see how the cleaning process works

Below is a picture of a typical large rack conveyor dishwasher from Silanos in Italy

This rack conveyor Dishwasher has the capacity to wash and dry up 4,600 pieces of crockery or 259 basket loads per hour.

This type of Dishwasher could be used in a Hospital, School, motorway service area, or airport service centre, anywhere where there is a large throughput.

They are also used to wash components in a factory situation and can be placed within a production line and controlled from a central point.

This particular machine is made in Italy by Silanos you can have a look at their range by following the link on the picture. Click and come Back! These machines are one of the largest you will come across and are a lot more sophisticated than the ones found in the home and the small restaurant, but they use the the same four factors of the cleaning process.

Which only goes to show that the only way to do more work requires more power, water, detergent, and machinery and if you compromise on any one of the factors the cleaning process will suffer.

Pass through hood type dishwashers for the medium size operation

The Pass Through hood type Dishwasher overview

The rinse tank boiler normally holds between 3.5 and 5 litres of water which is heated to 85ºC during the wash cycle and filled via the hot water supply. A rinse boost pump may me needed to increase the hot water pressure to the required 2bar for adequate rinsing.

The heater elements are normally between 3/6KW the lower setting would reduce the throughput due to the delay in heating the water to the desired temperature.

This is sometime accomodated by means of a relay which keeps either the wash tank or rinse boiler heaters off at the same time so that it can run on a 6KW supply.

The best way is to have 415V 3phase and neutral with at least 9KW supply which will work beautifully.

This will provide a machine capable of washing a basket of crockery every 1.5/3 minute to a very good standard.

The hot water rinse cycle may require a booster pump to provide the mechanical action to sluice off the detergent and soiling and sanitise the dishes.

The rinse is only for 15 seconds so disinfection will not take place due the lack of time see the disinfection page for more details

A range of tabling can be purchased ready made or bespoke to fit any kitchen wash up area. The more space the better for the work being completed. Disinfection and sterilisation issues for dishwashers

The Front loading tank dishwasher with tables, rinse arm,water softener, and built in rinse tank boiler.

The Front loading single basket tank dishwasher, the most popular dishwasher in the world

Typical front loading dishwasher exploded view

One of the most popular style of dishwasher in use throughout the world is the single basket, front loading tank dishwasher, with built in rinse tank boiler, which will wash 18 plates in a basket every 2/4 minutes.

There must be hundreds if not thousands of manufacturers through out the world building a similar machine with various features and benefits.

Because it keeps a tank of wash water in the bottom of the machine of about 25/30 litres depending on model which is replenished by the rinse water after each wash cycle along with a squirt of detergent, it works quite well for most operations.

Where the problems start is where the electrical power supply goes below 6KW or 30Amps 220/250 volt.

If it is connected to a 13A supply the machine will not recover in time between washes and the water in the boiler and wash tank will get cooler.

That is unless a hold relay is operating which stops the wash from starting until all the temperatures are up to their level.

Normally the wash tank is kept at 60ºC and the rinse tank boiler which holds about 2.5 to 3 litres is at 85ºC. This will ensure the correct wash parameters but will mean it will be about five minutes between each wash cycle.

The Answer is always connect to an adequate power supply at the outset, at least 6KW for this type of dishwasher.

Things to look out for when purchasing your dishwasher is does it look well built, have a look at the inside wiring to see that it is neat and tidy, are the pumps adequate in size to pump thousands of gallons of hot water day after day for many years?

Is it made of stainless steel inside and out, with good strong wash and rinse arms with easy to clean jets?

Have you arranged adequate power supply and hot water to the site with drainage below floor level to get the waste water away?

Plan the area for the wash station in advance and you will sidestep all the problems at a stroke.

You must have enough space for the kitchen porter to work, loading and unloading the machine, with racks to place clean crockery close by.

This picture shows the typical layout for a dishwasher inside the wash tank showing the wash and rinse arms within a stainless steel pressed wash tank.

It is always best to look for a wash tank that has been pressed from on piece of metal which will mean no welding failures down the line.

Where a wash tank is fabricated from several components look out for high quality finish to the welding, with no lumps or trapped slag which could cause trouble in the years to come.

Small front loading fresh water two basket commercial dishwasher.

This machine is capable of washing and drying 740 pieces of crockery every hour, to a very high standard every day.

It uses a unique way of juggling the sinners diagram (mechanical action,temp,time and chemical action) to get the best wash in the time allowed, and because it holds two backet loads it gains on the single tank machine.

And although the wash time is longer than 2/3 minutes, the dishes are cleaner with no smelly water left in a tank all day with the heaters on. A very sensible machine.

The benefits of this type of machine are that because it uses fresh water from the hot supply for each wash and rinse with heating elements similar to the domestic version only high power 6KW 240/415V single or three phase and neutral.

It is able to wash 30 dinner plates 24 cups and saucers and two small baskets of cutlery, which is equivalent to three basket loads from any other machine, in 5-18 minutes (depending on wash cyle and power supply, and water temperature inlet.

A large amount of dishes can be washed and dried to a very high standard very quickly and efficiently every time with this machine clean and ready to go from the off.

About 740 pieces per hour!! Not counting the cutlery. Go Check out Miele Professional UK Ltd This machine is the basis for a large range of machines that have been designed to wash anything from dental instruments, surgical instruments, laboratory glassware, printed circuit boards, just about anything that needs a high quality wash and even a high temperature rinse for thermal disinfection.

I have installed many of this type of machine in the ward kitchens of hospitals throughout the UK, where they provide clean and healthy crocks every day for many years trouble free service.

Miele do seem to have it down to a fine art when it comes to a machine of this size.

Take a look at their site. There is no better way to combat MRSA and control infection in an institutional kitchen than with this type of machine at your elbow.

As long as the staff wash their own hands and do not re-contaminate the dishes after the wash process, infection control managers should see an improvement in the health of their patients. Miele Professional UK Ltd Or, have a look at one of their dealer suppliers within the UK for more information and come back here soon.

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