- Buyer's Guide
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While spot-free systems are fast becoming standard equipment for in-bay automatics and exterior tunnels, they are slower to gain approval in self-serve. This is unfortunate, because having a spot-free rinse system available at a self-serve wash makes it much more appealing to the customer.
This is especially true to the discerning consumer who knows a ratty bath towel, which could scratch the car, won’t be needed because the final spot-free rinse doesn’t require drying.
Why spot-free for my self-serve?
First, by providing the option of a spot-free rinse, the consumer will opt to purchase the additional time necessary in the bay to utilize this feature, generating additional profit for the operator.
Second, the customer will not be abusing the time in the bay towel-drying the vehicle.
Using bay signs and banners, the operator can educate the consumer of the value of spot-free rinsing. Many consumers who have experienced a wash utilizing spot-free rinse feature will look for this feature when selecting a carwash in the future.
The standard sizing for a spot-free rinse in a self-serve vehicle washes is 100 gallons per bay, per day. Historically spot-free rinsing at these low volumes was addressed with de-ionization (DI) systems.
DI removes dissolved solids from the water with charged resin contained in exchange or onsite self-regenerating systems. Exchange tanks are getting increasingly harder to find and are prohibitively expensive in some areas. Onsite self-regenerating systems have their own set of problems with the need to handle and store dangerous chemicals for regenerating the resin in the DI tanks.
The overwhelming choice for making spot-free water in the automatic or exterior tunnel market is the reverse osmosis (RO) system. A RO system is a simple addition to any vehicle wash location and will increase customer satisfaction, generate additional profit, and create customer loyalty.
How does RO work?
On the technical side, all RO systems work in much the same way. Tap water is introduced into a pump, which increases the pressure to 180-250 psi (pounds per square inch) and forces water through a membrane. It is recommended to pre-treat tap water before it goes into the RO system. Some water conditions will require additional pre-treatment, so consult the equipment supplier.
Because most municipal water systems use chlorine as an anti-bacteria treatment and membranes do not tolerate chlorine, it is necessary to remove the chlorine before the RO. A simple, activated charcoal filter tank works for this purpose and most RO manufacturers include this as part of the system.
All systems will have some form of a pre-filter, usually 5-micron, to separate the larger solid material from the water. The RO membrane or pump will either plug or be damaged if the larger particles are not first removed by the disposable filter.
This pre-filter needs to be changed at least once per month and some water conditions require more frequent changes. When pre-filters are not changed regularly, RO systems will produce poor product water quality and often a significantly lower production rate.
The most common size membrane used in carwash applications is 4x40 inch, which requires 5 gallons across the surface of the membrane for every gallon of product or permeate water produced.
In years past, most operators would just send the four gallons of “bad” or concentrate water down the drain. Today, water costs are expensive and some locations are limited to how much water they can send to the sewer. Most, but not all, RO units re-circulate a portion of the concentrate water back into the inlet stream. Of the five gallons you start with, one gallon of product water goes into the RO storage tank, one gallon of concentrate water goes to the drain and three gallons are re-circulated.
RO systems are typically sold by the amount of water they produce in a 24-hour period. This rating is usually at optimum performance with 77-degree feed water. If your calculations are close, upsize your storage tank by selecting the next larger unit.