Tech Corner: Differences between Injectors and Proportioners

It’s not uncommon to find people using the terms “Injectors” and “Proportioners” interchangeably, however, that’s not correct. To clear up some of the common confusion, we’ve broken down the difference between the two below.

Injectors and proportioners are similar in the fact that they both use the venturi effect to create vacuum. The venturi effect is: “Water flowing through a nozzle with the stream of water going across a port that will draw in air or chemical into the water stream.” The difference, however, is that injectors are installed in line with the water source and proportioners are installed at the end of the water source.

Injectors are tricky to size because of back pressure. To properly size an injector you have to have the pressure of your water line the injector is going to be in and the flow rate at the end of the line your injector is in. An injector has to have a small amount of back pressure to prime. If you have too much restriction at the end of your line, the injector will not draw because the back pressure is too great. This occurs mostly when there is some kind of nozzle attached to the discharge. Also if there is no back pressure at all the injector cannot prime.

Just remember when sizing an injector get the water source pressure and the flow rate of the discharge. If there are multiple nozzles on the output, measure the flow rate of each nozzle and add that up to get your total flow rate in GPM (gallons per minute). Never size an injector by the size of the pipe you are installing it into.

As mentioned previously, Proportioners use the venturi effect as well. With the proportioner located at the end of the water source, this is typically used to fill quart bottles or buckets. At DEMA, we use a 1 GPM proportioner to fill bottles and 4 GPM proportioner to fill bucket. The proportioner controls the flow rate of the water source. As the proportioner is at the end of the water source, back pressure does not have an effect on the proportioner.

Have questions about injectors, proportioners, or anything else related to chemical dispensing? Contact your Regional Sales Manager or call our Technical Service department at 1-800-325-3362.