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Injection Sprayers: The Straight Scoop

May 10, 2005
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Of all the available accessories for the professional carpet cleaner, and particularly the truckmount user, the injection or in-line sprayer is certainly one of the most popular.

With several models available from different manufacturers, there is a lot of information and, unfortunately, a lot of misinformation shared among professionals concerning the workings, problems, and virtues of the injection sprayer.

A Brief History
In the late 1970s I was attending a carpet-cleaning class in which industry icon Ron Toney suggested it would be a good idea to mimic the lawn-care system for a carpet pre-spray, in which a container of fertilizer or weed killer is attached to the end of a garden hose and the chemical is injected into the water stream before being sprayed onto the lawn. I thought this had some real merit, so I went back to the shop and started working on a system.

Certainly, the idea of using a venturi-type injector goes much farther back than the late ‘70s. In fact, the beginning of understanding of how a liquid venturi system works dates back to 1724, when Daniel Bernoulli investigated a problem begun by Sir Isaac Newton concerning the flow of water. In 1738, his work "Hydrodynamica" was published. In this work, he applied the conservation of energy to fluid mechanics problems. The Bernoulli Equation, used to calculate and analyze airfoil and the forces that create negative air pressures as air passes over surfaces, such as airplane wings, also applies in part to liquid flows and the venturi effect that is applied in our injection sprayer valves.

What is an Injection Sprayer?
The injection sprayer, or in-line sprayer as it is sometimes referred, is designed to be attached to the solution line from a truckmount or portable extraction unit. The container on the sprayer holds a concentrated solution (e.g. traffic lane pre-spray, carpet protector, deodorizer, etc.) that is injected and mixed into the solution from the extraction machine as it passes through a valve. With the two solutions mixed, the correct proportion of the diluted chemical can then be sprayed on the carpet.

The valve on the sprayer uses the venturi principal to draw the chemical into the solution stream. As the solution approaches the valve, it is first filtered, then moves into the valve and water nozzle that reduces the volume flow and increases the flow speed. As the fluid passes through this restricted area it creates a negative pressure or suction that draws the concentrated chemical product from the jug through a filter and into the solution stream.

There are basically two designs that are used in our industry. One design is preset, offering a consistent dilution ratio normally set at 1-to-8. The common way to alter this dilution ration is to change or remove a small metering tip positioned at the bottom of the valve. The reliability of this valve comes from the fact that there are no moving parts in the valve itself, and only one small check ball that moves on the chemical suction side under the valve.

The second design has a dilution adjustment that is changeable on the fly. A simple turn of a knob or disc will adjust the dilution from a 1-to-4 ratio up to a 1-to-64 ratio, and everything in between. This sprayer is especially appreciated when pre-spraying a traffic-lane area and finding excessive soil, an area where you would like a stronger concentrate of chemical while decreasing the amount of water applied. A simple turn of the knob can take the dilution from 1-to-32 down to 1-to-16 and then right back again for spraying the remainder of the carpet.

How It Works
The No. 1 use for the injection sprayer is the application of traffic-lane pre-sprays. In addition to traffic-lane cleaners, these sprayers will apply any water-based chemical that is concentrated and can be diluted to one part chemical to four parts water or greater. Recognizing the flexibility of the injection sprayer, many professionals now use the sprayer to apply carpet protectors, deodorizers, hard-surface cleaners and even carpet dyes.

The injection sprayer can enhance efficiency by allowing the operator to quickly change from one chemical to another without having to clean out the sprayer. Simply take off one jug of chemical and replace with another. The joy of working without the hassle of pumping, running electrical cords, or running out of a battery charge helps you accomplish better work faster on every job. And having constant pressure allows for constant and even application of your solution.

It is a fact that cleaning with higher temperatures creates a distinct advantage when it comes to removing just about all types of soil. Since injection sprayers have a constant supply of hot water coming from the machine, hot solution is always applied directly to the carpet.

Injection sprayers will put down an increased amount of solution with increased pressure. The increased solution allows you to move faster (always a good idea if earning more per hour is a concern), and the increased pressure creates better penetration into the soiled carpet as you spray.

So, if you are running your machine at 400 PSI, you will be spraying at 400 PSI with your injections sprayer, right? Wrongo Bongo, hold your horses, hold the boat.

DuPont Input
Approximately four years ago, DuPont tested the Hydro-Force Injection Sprayer for use in applying DuPont-branded protector to carpets. Their tests were conducted with the Hydro-Force Injection Sprayer, but the conclusions may be applied to injection sprayers whose design and parameters match the Hydro-Force.

DuPont had two main concerns:
1. Safety. Too much pressure causing vaporizing of the spray and the possibility of exposing the operator to the vaporized spray.
2. Even application and proper dilution using their protector with an injection sprayer.

To address the safety issue, the DuPont scientists set up a controlled environment in a contained area and used a stock injection sprayer. The individual performing the spraying wore sampling apparatus to measure the airborne vapor. I will spare you the intricate details of this extensive two-day testing and get right to some of the conclusions. Please understand that I do not represent DuPont, and these conclusions are my interpretation of the results.

A truck-mounted machine was set up to run at 400 PSI with 150 feet of 1/4-inch pressure line running at 200 degrees at the machine. All measurements were checked with duplicate gauges and meters. We found that at the end of the 150 feet of pressure hose that we were running 375 PSI and 180 degrees. With the injection sprayer attached at the end of the pressure hose, drawing a concentrate of protector and spraying, we found the out-going pressure to be 80 PSI. Yes, that is correct. Using a number 6506 jet opening at the end of the spray wand, (the same jet that has been used for our injection sprayers for several years) the injection sprayer was outputting 80 PSI. We also measured the volume output to be 3/4-gallon per minute.

While 80 PSI is still substantially more pressure than the typical pump or electric sprayer will put out, it is also much less than what the machine pressure indicates. With the pressure being in the safe range of 80 PSI and the larger droplet size put out with the 6506 jet, very little spray was vaporized, therefore creating no dangerous risk to the operator.

Next month, we will get into meatier matters concerning injection sprayers, and answer some common questions, such as, "Why does an injection sprayer stop working?" "What effect does solution temperature have on injection ratios?" "Does an injection sprayer work differently in Denver than it does in Los Angeles?" And for the tens of thousands of professionals who use and love their injection sprayers, I will offer some ideas on how to get even more performance and usefulness from your sprayer.

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