EnviroSpec’s Technical Library

Section: Chemical Injectors
Article: Facts about Down Stream Injectors

There are many operational limitations that have to be considered to understand the function of the downstream injector in the field. To be successful working with a downstream injector it is important that you understand these operational factors.

 Section: Downstream Injectors – Draw Rates

Advertised chemical draw rates are obtained under laboratory test conditions and cannot normally be obtained under field operating conditions. These draw rates are obtained with no back pressure on the injector outlet, meaning no hose, gun or nozzles are installed. The injector is operated with the exact water flow for peak performance, a short chemical tube with a low viscosity product, usually water being drawn. So it is unrealistic to expect field draw rates to be equal or even close to the advertised draw rate. These tests are conducted with the manufacturers efforts concentrating on getting the best possible result, because the average consumer is going to buy the injector with the highest advertised draw rate. So the injector with the highest advertised draw rate is probably the highest drawing injector, just don’t expect actual draw rates of more than 10 to 14%. And that draw rate will be reduced further with long lengths of hose, too small a soap nozzle, or mismatched water flow.

Section: Field Diagnosis and Repair – Chemical Injectors

Many variables affect the performance of a chemical injector. Practical field service involves the following steps. If there is no Chemical draw, first establish that the chemical container isn’t empty, or the chemical line hasn’t fallen out. Make sure the injector adjustment knob is open (turned out counterclockwise). Make sure the high-pressure hose isn’t too long. Replace the injector with the spare. If it works, go back to work. If that doesn’t work disconnect the trigger gun and nozzle from the hose. Test to see if chemical is drawn through the open hose. If it is, replace the trigger gun assembly and/or chemical nozzle. If the chemical line and filter weren’t replaced with the injector, determine if there is a blockage in them. Clear any blockage or replace the line or filter. Also check for loose fittings and cracks. If the injector is allowing water into the Chemical line replace the injector with a spare and go back to work.

Section: Installation of Chemical Injectors

The best place to install the injector is typically at the outlet of the pressure washer just prior to the high-pressure hose. If the equipment has a ball valve that allows the water to be turned off without shutting off the machine, be sure to install the injector after the ball valve to enable injector replacement without shutting off the equipment. Always install quick disconnects on the injector for quick change out. Always have a spare ready to replace the injector being used. Have quick connects, chemical tubing, and a filter already installed on the spare to reduce any potential down time. Most injectors have an arrow that indicates the direction the water flow should travel as it goes through the injector. Installing a chemical injector facing the wrong direction will definitely reduce its effectiveness.

Section: Pressure Hose Length for Injectors

High-pressure hose that is downstream of the injector exerts back pressure on the outlet port of the injector when water is flowing. The friction of the water stream contacting the inner tube of the hose creates the back pressure. The longer the pressure hose the more friction occurs and the greater the back pressure created. The pressure exerted on the outlet port of the injector adversely affects the venturi action of the injector. Because of this fact, the shorter the pressure hose is, the less back pressure is produced, and the higher the chemical draw will be. The pressure hose inner diameter also affects the back pressure created. Industry standard for high-pressure hose is 3/8″ inner diameter. In some cases a ¼” I.D. hose is preferred because it is lighter. Remember that the friction of the water going through a smaller hose will create more back pressure and very likely affect the injector chemical draw. A larger ½” I.D. hose can be helpful when it is necessary to run a long high pressure hose while still being able to draw chemical. The drawback is the hose weight. Most downstream injectors work the best in the field when used with 50 to 100 feet of 3/8″ I.D. pressure hose. Some will continue to draw chemical at 150 feet of hose, most will no longer draw with 200 feet of pressure hose. As the hose length increases, the percentage of chemical drawn into the water stream decreases. Because of this, in situations where a high percentage of chemical draw is important to the result of the wash job, a shorter hose is beneficial. A trick of the trade when a long hose is needed along with downstream chemical injection is to move the chemical injector itself down line in the high-pressure hose. The pressure on the injector outlet port is what affects the chemical draw, so as long as the hose in front of the outlet is kept to a minimum, the hose behind the injector won’t inhibit chemical draw. There is a limit to this trick however. If enough hose is installed behind a downstream injector to actually reduce the water flow to the point where there isn’t sufficient water to create the venturi action in the injector body, then injection won’t occur.

Section: Shop Diagnosis and Repair of Chemical Injectors

The debate will continue as to the practicality of repairing chemical injectors. When a downstream injector can be purchased for less than twenty dollars, is it worth rebuilding it? Most rebuild kits contain a ball, spring and o-ring; some also have the nipple or adjustment knob. Most don’t contain a replacement venturi nozzle. The more the complete injector costs, and the cost the rebuild kit, are determining factors in deciding this issue. If the injector isn’t producing any chemical, first eliminate the surrounding factors as possible problems before rebuilding the injector. Inspect, clean and/or replace the chemical tube, fittings and filter. Test without the trigger gun and nozzle. Sometimes there can be something in the trigger gun or nozzle that isn’t allowing the pressure to be reduced enough for the injector to function. Isolate where the problem is and replace the part. This test can also determine if because of venturi nozzle wear the injector is worn to the point where it won’t function well enough to be used anymore. If available, replace the venturi nozzle. Some can be threaded out. Some are simply pressed into a cavity in the injector body. Replace the quick connects if they are worn. If the injector is allowing water into the Chemical Line, first unscrew the nipple or adjustment knob from the injector body. If the spring and ball appear to be in good condition, check to see if the o-ring is out of place. If it is reinstall it and reassemble. If the o-ring is missing or damaged, or if the ball or spring is not in new condition, rebuild the injector. To rebuild the injector, unscrew the nipple or adjustment knob from the injector body. Find and replace the spring, ball and o-ring. Install the components; working furthest away from the injector body first, the order is, o-ring, ball, and then spring. Use pipe thread sealer on the threads of the nipple or adjustment knob, and then thread back onto the injector body.