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Chemical Dispensing Equipment for Laundries 

By Nathan Schiff, PhD
Associate Editor - Institutional

There is a commonly held belief that if a recommended amount of product does the job, more will do it better and faster. When a problem arises, machine operators tend to overuse chemicals instead of questioning a product's suitability for cleaning a particular garment. Because this practice can damage garments and reduce profits, automatic chemical dosing systems have become an integral part of most OPL (On Premise Laundries), and more so for commercial laundries. These systems not only provide accurate and consistent chemical dosing, but also eliminate the need for physically handling hazardous chemicals.

Several companies have developed dosing systems, however the most reliable and user friendly ones which I have been exposed to, are manufactured by Knight Equipment (Knight, Inc, a unit of IDEX). This article describe one such simple system for use in OPL Laundries.
Basic Dosing Assembly

The basic On-Premise Plus™ assembly unit has 4 chemical pumps (but can hold 6 if needed), which are independently controlled. This allows 4 different pre-set amounts of chemicals such as builder, break, bleach and softener, which make up a wash formula for a specific type of garment, to be independently dispensed. The unit is supplied with a cable-connected controller which programs the amount of chemical each pump should deliver and when set, it is capable of storing in its memory, 8 different wash formulas.

The Peristaltic Pump
The heart of the dispenser is the peristaltic pump. As the motor rotates, an triangular-shaped disk attachment, compresses and relaxes a squeeze tube, 3 times during each rotation. This action creates a vacuum on the chemical supply side of the squeeze tube and pressure on the chemical delivery side. In effect, chemical is lifted out of the container and pumped towards the washing machine.
The electronics of the dosing unit are also connected to the washing machine's computer output terminals. At appropriate times during the wash cycle, electrical impulses from the washing machine signal the dosing unit. This in turn, activates the
pumps to deliver the precalibrated amount of specific chemical through their designated pumps. The On-Premise Plus™ system can deliver 10-20 oz/min of chemical and is therefore capable of servicing washing machines having a capacity of 50 -175 lbs.

The Controller
The amount of chemical which a pump can deliver is dependent on the size of the pump, the size of the squeeze tube (diameter) and the time during which the pump is running. The longer the pump runs, the larger is the quantity of chemical injected into the washing machine. Generally, a pump should be capable of delivering the required dose within 30 to 45 seconds, and with this rule of thumb, pump sizes are determined.

The time that a pump needs to run is determined by running the pump, prior to hook-up, for 30 to 45 seconds. The chemical run-off is physically collected and measured in a calibrated cylinder. This is followed by minor timing adjustments until the exact chemical dose is obtained. The information is then fed into the controller for each pump used, in a designated wash formula.
Installation of a Pump Assembly

Most chemical companies supply and service their equipment on a no fee basis, provided that the laundry uses their chemical products exclusively through the equipment. However both, the chemical company and the laundry have inherent responsibilities to assure that the equipment functions properly.

The company's responsibilities include:
1.    Installing the assembly and hooking its electrical components to the washing machine.
2.    Calibrating the pumps, by physical means, then feeding this information to the controller. A pump's output is very dependent on the viscosity of the liquid being delivered. The more viscous (thicker) a product is, the harder it is to pump and less is delivered. For this reason, whenever products passing through a pump are changed, the previously calibrated pump, needs to be re-calibrated to insure continued, uniform and accurate dosing.
3.    Checking the basic operation of the pump assembly and insuring that the signals coming from the washing machine are recognized by the dispensing equipment
4.    Changing or adding different wash formulations as required by the laundry manager.
The Customer's Responsibilities
Well designed dispensing equipment requires very little maintenance, except for the greasing of the squeeze tube every 4 to 8 weeks, and their replacement when worn out.

Replacing a tube involves unscrewing the plastic face plate of the assembly, pulling out the old tube and sliding in the new one. The whole process takes 10 -15 minutes, and saves a lot of potential downtime.

1.    Always store the chemical containers as close to the dispensing equipment as possible. The hose sitting in the chemical container should never be more than 50 feet long.
2.    Maintain the squeeze tube by regular greasing and replacement when worn out
3.    Maintain a small inventory of extra squeeze tubes, should replacement be necessary.


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