Conveyor-rack dishwashers come in one, two, and three-tank models and are capable of washing 125 to 360 racks of soiled dishes per hour. Racks that hold the dishes move on a continuous chain conveyor through each step of the automatic wash and rinse cycle. The operator simply loads the racks and feeds the machine with one rack after another.
In the lower volume single-tank machine, the tank holds the wash water and detergent mixture. Some of the rinse water, supplied by the booster heater, is then drained into the wash water tank. Double tank machines are designed to hold the wash water while the other tank holds the rinse water permitting much quicker washing cycles. Triple tank machines use another tank for pre-wash cycles to remove food. Blowers and heated dryers are available.
A two-tank machine has a detergent wash, a hot-water rinse, and a final sanitizing rinse. A three-tank machine includes a pre-wash cycle, eliminating the need to spray-rinse flat tableware manually. These machines are best suited for use in large capacity facilities, such as hotels, hospitals, colleges, and anywhere that 200 to 400 meals are served daily. The typical cleaning cycle lasts one minute, and, on average, these machines use about 415 gallons of water per hour. These figures vary by manufacturer, of course.
Flight Type Machines
Flight-type machines are also called “rackless” or “belt conveyers” and are the monsters of the dish room, capable of washing as many as 24,000 dishes per hour. They are the primary choice for large institutions.
They come in double, triple, and sometimes custom-built four-tank units. Double tank models are preferred for schools and similar facilities where the food is simple and the variety is limited. The two-tank machine consists of a wash tank and rinse tank. Three-tank models have tanks for prewash, wash, and rinse cycles. All flight type machines have a final sanitizing rinse cycle.
Door-type, or stationary rack, machines are one of the most common types of ware-washers because of their compact size and versatility. They are used by small operations with fewer than 150 seats and can wash up to 60 racks of soiled dishes per hour.
Door-type dish-washing equipment is best suited for facilities serving 100 to 200 meals a day. The maximum capacity for high temperature machines is roughly 65 gallons per hour. Most machines consume between 70 and 90 gallons of hot water per hour, while low temperature machines average 110 gallons per hour. This type of dishwashing equipment is designed to sit between two tables: a soiled loading table and a clean table on the discharge side of the unit.
These free-standing door-type dishwashers have a heated tank for storing wash-water at the proper temperature. Water circulates by means of a motor-driven pump through spray pipes or nozzles. These may be located above, below, or both above and below the dish-rack. This unit includes a cover, hood, or door. Fresh hot water from a separate set of nozzles located both above and below the rack provide the final sanitizing rinse. A typical wash cycle lasts about 45 seconds with an additional 12 second rinse cycle.
Single Tank Under-Counter
The smallest capacity dishwashing equipment design presently on the market is the single tank or under-counter unit. This model is ideal for smaller establishments such as taverns and bars that generally serve no more than 100 meals a day. The under-counter model washes between 17 and 21 racks of dish-ware per hour and has a maximum water requirement of about 40 gallons per hour. Most under-counter dishwashers operate with a two-and-one-half minute cleaning cycle. Overall system efficiency depends on proper maintenance, adequate ventilation, correct water temperature and full-load-operation.