Evaluation of Input-Based Foam Proportioner Testing Systems

The Evaluation of Input-Based Foam Proportioner Testing Systems research effort was initiated to examine the viability and accuracy of input-based methods for confirming foam proportioner system functionality on aircraft rescue and firefighting (ARFF) vehicles. Output-based tests were conducted using test methods defined in National Fire Protection Association 412, “Standard for Evaluating Aircraft Rescue and Fire-Fighting Foam Equipment.” Input-based tests were performed according to manufacturer guidelines. 

Output-based test results showed a small variation in measured proportioning percentage between different discharges and between different measurement methods. An error range was used to determine the accuracy of the input-based systems compared to output-based tests. The error range was based on the measurement error of the digital refractometer device used and the measured concentration of the discharge sample for each output test. If the results from an input-based testing method fell within this range, it was considered to correlate to the output-based results for this research effort.

Overall, a greater correlation and testing accuracy exists at a 3% proportioning rate than at a 6% proportioning rate. Similarly, there is a greater correlation when using electronic proportioning systems than when orifice plate proportioning systems are used with input-based proportioning test methods. This is thought to be as a result of the system’s ability to dynamically respond to any operational variations (e.g., pump pressure or flow rate). All testing was conducted using around-the-pump proportioning systems, and conclusions may not be applicable to other types of foam proportioning systems.