Understanding the Injection Sprayer

Of all the available accessories for the professional carpet cleaner, and particularly the truckmount user, the injection sprayer is certainly one of the most popular. The injection sprayer, or in-line sprayer as it is sometimes referred to, 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 (traffic lane pre-spray, carpet protector, deodorizer, etc.) which will be 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 or other surfaces.

As most professionals use an injection sprayer, I have often wondered about those who don’t. After doing some research with active users and those who work with other types of sprayers, I found some common concerns.

Understanding the Limitations - Pressure

Most injection sprayers will work over the full range of solution pressure that portables and truckmounts are designed to output. The solution coming from the machine passes through a restricted water nozzle which decreases the flow and increases the velocity, thus creating a negative pressure, or suction, to draw the chemical into the valve.

The incoming pressure has an effect on the actual ratio of chemical to water. Generally at lower pressures, say 200 PSI, the ratio may be one part chemical to seven parts water, while at 400 PSI the chemical-to-water ratio may be 1:8.

As the pressure goes up and the speed increases through the water nozzle, the ratio of chemical to water will decrease. Some in-house tests (and this is just a loose estimate) showed us that moving up from 400 PSI, you will lose approximately 10 percent chemical draw for every increase of 100 PSI, e.g. if you were drawing at one part chemical to 10 parts water at 400 PSI and increase your pressure to 500 PSI, your chemical-to-water ratio would be 1:11.


The temperature of your water as it passes through the injection valve may have an effect on your draw ratio. As water temperature increases, the molecules become more active and the density of the water decreases.

As more dense water (cold water) passes through the water nozzle it has the greatest ability to create suction, pulling more chemical into the stream.

As the less dense water (hot water) passes through the nozzle, it gradually approaches pure vapor, and the suction action can be totally lost when high, boiling temperatures are reached.

When designing and machining valves, one of the greatest challenges is to keep the valve drawing consistently while approaching the highest temperatures. Knowing that many of today’s machines are designed to obtain temperatures exceeding 220 degrees F, it was a particular challenge considering that the laws of physics could not be broken.

Once the water is hot enough to turn to pure vapor in the injection valve, all suction will stop. Since the water system on your truckmount is a closed and pressurized system, the water will not turn to vapor immediately when boiling temperatures are reached. The injection valve is part of the closed system; however, after the water passes through the nozzle, there is room for expansion and the very hot water creates cavitations as bubbles form, and this reduces the chemical draw.

The practical application of this knowledge on temperature comes in knowing that the valves are designed to run at higher temperatures and give accurate draw but, once the temperature at the injection valve starts to reach boiling (212 degrees F), the ratio can decrease and eventually stop.

Does this mean you should discard your injection sprayer if your machine is reading 220 or 230 at the machine? Absolutely not!

The pre-spray process usually occurs at the beginning of a job and at intervals throughout the job. In the beginning the machine is usually warming up, and this gives ample time to pre-spray before the machine is at its peak temperature.

When spraying in the middle of the job, it is important to remember that your hoses release temperature as the solution flows. Since the volume of solution goes down to half or less when using the injection sprayer, the solution is in the hose twice as long and has time to cool down.

You might also consider the possibility that the temperature gauge on your machine may not be accurate, or perhaps is measuring temperature at a point other than when the solution actually leaves the machine. Many professionals are using injection sprayers successfully with equipment that regularly exceeds 230 degrees at the gauge on the machine.


Water boils 212 degrees F at sea level, and 204 degrees F at 4,000 feet. Those of us that live and work at higher elevation will be slightly limited spraying at the highest temperatures.

Some professionals deal with this by keeping their machine at a maximum of 220 degrees at the machine – a very effective cleaning temperature.

For those who don’t have accurate controls, they may run their machine at lower rpms while pre-spraying, or put on an extra length of hose to allow the cooling effect before the solution reaches the injection valve.

Atmospheric pressure can also have a small impact on the draw. At higher elevations you will see a slight decrease in the draw ratio of chemical to water.

The Importance of Jet Size

Our service department receives calls quite often from individuals who have changed the spray jet on their injection sprayer and find that it no longer draws chemical. They may have changed jets because the old one was worn out (brass T-jets will wear significantly in 6 to 12 months under normal use), or they wanted to decrease the flow and put on a smaller jet.

When replacing the jet, make sure you replace it with the same size that was originally on the sprayer. The Venturi effect will be decreased or stopped if there is too much back pressure, and back pressure occurs when the jet size is too small.

Say a jet on an injection sprayer is stamped 6506. The first two digits, “65,” indicate the degree and angle of the fan pattern spray as in a 65-degree spray. The second two digits indicate the size opening: “06” is the size opening of the jet.

Never go smaller. Going to a larger size will actually, to a point, draw a higher ratio of chemical to water.


Most injection sprayers have screen filters built into the unit. If these filters become clogged the sprayer will stop working. It is also possible to have chemical clog filters on the draw side where chemical is pulled from the jug.

The only moving part in the standard injection sprayer is the ball spring combination that is located in the lower knob. It is possible for this ball to stick closed when the chemical used is particularly sticky or dries inside the valve.

If repair work takes place in this part of the valve, be sure not to lose the small, clear disk that seals the parts and keep air from intruding.

Efficiency and Effectiveness

Here are some hints for getting the most out of your injection sprayer:
  • Use a quality shut-off valve at the end of your solution hose. This allows for quick changes from your cleaning wand to the injection sprayer and then back again.
  • Carry an open end male quick connect in your pocket. If you would like to start your job using hot pre-spray, plug the quick into the end of your solution hose, open your shut-off valve and pump solution into your vacuum hose until it is hot. You may then hook up to the injection sprayer and spray hot solution immediately.

    The quick connect is also useful when changing over from pre-spray to protector. The major brands of protectors now come in bottles that readily fit injection sprayers.
  • Shut off any chemical injection at the machine. Plug in the male quick connect, and drain the solution hose of solution that may contain chemical, then hook up the sprayer and go to work with the protector.
  • Buy extra 5 quart containers and keep your products in them (make sure they are labeled properly) so you will not have to worry about filling and mixing while on the job.

    If your pre-spray is a thickened variety, consider cutting it with one or more parts of water in the jug. Thick solutions are harder to draw, and your ratios will not be accurate.
  • Consider an adjustable. Recent improvements in the knob and valves now keep the setting in a firm position adding to the accuracy. Whatever the dilution of the chemical you can get it tuned in with just the turn of a knob.

    Perhaps you are cleaning a very soiled Olefin Berber, and notice that in front of the couch there is a heavily soiled area. You never want to over-wet an olefin, so simply applying more pre-spray is not a good option. With the use of an adjustable sprayer, you simply turn the knob from a 1:16 dilution to a 1:8, spray the soiled area and then turn the knob back to 1:8.
I hope this has helped improve your understanding of the workings and advantages of injection sprayers. Your life is improved when you can increase your effectiveness and efficiency through the use of professional “gadgets.”

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