Rural Command: Tips for measuring both water & foam concentrate flow volumes

Calibrating the Proportioner: Tips for measuring both water & foam concentrate flow volumes
Story & Photos by Keith Klassen

Today’s electronic direct-injection foam proportioners are highly sophisticated machines. They’ve been through approximately 20 years of development, and countless incidents have proven their reliability. Some of these developments include improved electronics and components. They also have increased capabilities, allowing them to sense different parameters that increase the accuracy of the systems. However, if the proportioner isn’t appropriately maintained and regularly calibrated, its ability to produce the required percentage of foam solution will be compromised. This month, we’ll look at the steps required to maintain and calibrate an electronic direct-injection proportioner.

Maintenance First
Maintenance includes checking fluid levels and servicing strainers. The pumps on most electronic direct-injection proportioners are lubricated by oil, which should be checked and maintained during every truck check.
Strainers are typically placed between the foam tank and the proportioner to prevent foreign material from entering the pump. If the strainer becomes restricted, it will affect the pump’s ability to move concentrate. To prevent this problem, the strainer screen should be removed, inspected and cleaned a minimum of once every 6 months.

Checking the Modes
To proportion accurately, the system must correctly measure both water and foam concentrate flow volumes. To calibrate these values, the system must first be placed in the calibration or set-up mode. How to do this varies slightly between brands of systems. Some models require activation of a micro switch, while others require a sequence of buttons to be pressed. Refer to the manufacturer’s manual to determine the correct procedure.
After entering the calibration mode, several parameters can be selected. The two required to calibrate the correct system output are the water flow mode and the concentrate volume mode.

Water Flow
To calibrate the water flow, first select a discharge from which you can flow a known volume of water. This discharge must be plumbed off of the foam manifold in order for the flow to be measured by the proportioner. Place the proportioner in the calibration mode, and select the water flow setting. Flow the line and use a pitot gauge to measure the specific volume of water. This volume should be close to the volume most often flowed in normal operations. For example, a brush truck would be calibrated at lower flows than a structural pumper. While the line is flowing, note the volume reading on the proportioner. If it doesn’t match the actual flow, adjust the reading to the correct amount. Be certain to save any changes.

Foam Concentrate Flow
To calibrate the foam concentrate flow, a known volume of concentrate must be pumped into a calibrated container. You can do this by switching the valve that controls the output from the proportioner pump from the “inject” position to the “bypass/calibrate” position. Then place the proportioner in the calibration mode and select concentrate volume. The proportioner can now be started and a specific volume (i.e., 1 gallon) pumped into the container. The reading on the proportioner should now equal the volume actually pumped. If the reading does not agree, adjust the proportioner reading. Rerun the test to help ensure accuracy. As with the water flow, save all changes prior to powering down the proportioner. Switch the valve back to the inject position after calibration for normal operations.

Final Thoughts
Calibration of the proportioner should be done a minimum of once a year. Tip: Do the calibration in conjunction with the annual pump test. Keep in mind that the accuracy of the proportioner is directly related to the accuracy of your calibration. Conducting regular and accurate calibrations will ensure that the system works correctly when needed on an incident.

Keith Klassen is a career captain with the Summit Fire District, a rural combination department bordering Flagstaff, Ariz. He has 33 years of volunteer and career experience in both structural and wildland firefighting, and a background in mechanical and vocational education. Klassen is also an international fire service instructor and a member of the IAFC.

Copyright © Elsevier Inc., a division of Reed Elsevier Inc. All rights reserved. SUBSCRIBE to FIRERESCUE

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Comment by Ben Waller on September 30, 2010 at 10:45pm
Most onboard foam systems have a flow meter that will measure either water flow or foam solution flow very accurately - within 2 or 3% of the flow volume. The easiest way to tell the water volume you're flowing is to simply look at the flow meter.

If you're flowing 100 GPM, it's easy to calculate the foam concentrate flow.
If you're using a 3% concentration, you're flowing 3 GPM of foam concentrate.
If you're using one of the newer 1% concentrate foams, you're flowing 1 GPM of concentrate.

If your foam system flow meter is reading 100 GPM and the self-calibration has been run, you're flowing between 97 GPM and 103 GPM - at least according to the system manufacturer.

3 GPM up or down from the calculated GPM isn't a problem.

The key point is to spec the onboard foam system with a flow meter and make it easy on the pump operators.

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