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Circulating cleaner carwash water

October 11, 2010
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For vehicle washing, water is the primary means of rinsing the dirt, road grime, salt and snow off the surface of the vehicle during the cleaning process.

All soaps use water as the delivery medium from the chemical station out to the vehicle to assist in breaking up those contaminants. The higher the quality of water used the higher the quality wash delivered.

Water types
There are three types of water that can be used in vehicle washing:

1. Fresh water: This can be tap water, either from a municipal water supply or private well. It can range in quality from great to terrible.

Some of the symptoms of terrible tap water are:

  • High total dissolved solids (TDS);
  • Either too high or too low of a pH reading; 7.0 to 7.4 would be neutral and the ideal.

Some other indicators of water quality are:

  • Is the water turbid or cloudy?
  • Is there Iron present in the water?
  • What is the hardness of the water?

Recognizing which problems or issues your fresh water source has will help you determine what equipment you’ll need and how you can improve your site’s ability to deliver a quality wash.

Water is an increasingly expensive commodity, and fresh water use in a vehicle wash application should be carefully considered.

2. Reclaim water: Reclaim water is water that has been used in the wash process, then cleaned and reused. This is accomplished with a reclaim system.

In self-serve applications, a reclaim system has a limited benefit; with all the water for the wash coming through the wand at approximately four gallons-per-minute, and an average of four minutes of actually being on, a vehicle is washed with 16 gallons of water.

With using fresh or spot-free water for the chemicals, soaps, and either fresh or spot-free for the final rinse, at best you will reclaim half of the water.

3. Spot-free water: This is water that either naturally or by processing has a total dissolved solids (TDS) count below 20 parts-per-million (PPM).

The overwhelming majority of spot-free systems in current use are reverse osmosis (RO). There are several factors to consider in sizing an RO system.

How much spot-free water will your wash equipment deliver? One hundred gallons-per-bay, per-day is a generally used gauge for a self-serve.

If your site has an in-bay automatic, a spot-free selection on the system is usually a great option. By adding a little more storage, the system that you use with your automatic will provide enough spot-free for your self-serve bays as well.

The musts
All systems should have some form of pre-treatment; a carbon filter for chlorine removal and a five micron pre-filter are the most common.

Chlorine will damage the membrane very quickly and it is important to remove it from your feed water. Suspended and dissolved solids in water are measured in microns.

But, how big is a micron? The smallest particle that can be seen by the human eye is approximately 40 microns; the diameter of a human hair is 50 - 75 microns.

A five micron pre-filter will remove the suspended solids down to that size. This material would plug a membrane very quickly; however, the inexpensive easily-changed filter will prevent this.

Is there more?
Your system should also have gauges to tell you the pressures you are operating at, a minimum of the tap pressure and the pump pressure. You will need some means to control the pump pressure — usually a valve.

Flow meters are needed to show the amounts of water produced and rejected. Typically for every gallon you produce you will need to reject a gallon to the drain.

The gallon drained will carry some of the dissolved solids stripped from the gallon held, and will help keep the surface of the membrane from fouling.

The ideal volume of water through a four inch diameter by 40 inch long membrane, the most common size, is five gallons for every gallon of product water produced. Therefore, a pump large enough to deliver that volume of water at adequate pressure, usually around 180 PSI, is necessary.

One of the most common mistakes is sizing the pump for the one-to-one ratio of product to reject, and not allowing for the five-to-one volume.

There are systems that provide for that five-to-one ratio, but dump the four gallons to drain, the days of dumping four gallons to make one gallon of product should be long past.

In the ideal system the balance of the five gallons re-circulates back to the inlet. This does raise your inlet TDS some, but as long as you are below the 20 PPM TDS at your product water storage you are making spot-free water.

Deciding on delivery
Delivery of spot-free in self-serve applications varies widely. Some will deliver:

  • Through the high-pressure pump system;
  • Through a dedicated pump with solenoids for a medium pressure, 150 PSI, or
  • Through the spot-free equipment supplier.

When making a decision on spot-free water, knowing how it will be delivered to the bay will help tremendously.

The majority of systems use the medium-pressure option. Customers who are used to the high-pressure wash and rinse may perceive the lower pressure as not being as valuable and therefore may require some education.

Bay signs describing the spot-free process and benefits are a good investment. The major benefit to the consumer is the fact that he or she will have a spot-free rinse and won’t need to worry if all the water has not dried off their vehicle.

With the medium pressure the spot-free water will flow through the wand at approximately 1.4 gallons-per-minute, to get a good rinse you would need about six gallons, or four minutes.

Post signs to help keep the customer informed of this and they will stay for the extra minutes which means more bay revenue.

Invest the time
As always, when selecting equipment you need to research your options thoroughly.

Is it well supported? Is there a local distributor that you know who can maintain and support you and the equipment? Will it interface with your existing equipment?

Your equipment supplier should have a good basic understanding of the use of water and can help guide you in your selections of equipment to make your wash a success.


Charles Borchard is the vp of operations for New Wave Industries, the manufacturer of Pur-Clean Spot-free Rinse Systems and Pur-Water Water Recovery Systems and is in his 16th year in the water treatment business.

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