Which two devices are commonly listed as flow meters in fire service descriptions?

• A. Post Indicator and Gallons Per Minute
• B. Stem and Yoke
• C. Pressure Governors and Electronic Pump Controller
• D. Spring Probe and Paddlewheel

Answer: (D)

Flow meters in fire service pump descriptions are the tools used to estimate how fast water is moving through a discharge, essentially the gallons per minute being delivered. The two devices most commonly listed for this purpose are the paddlewheel and the spring probe.

A paddlewheel flow meter sits in the water stream and has a small wheel that spins as water flows past it. The rotation rate is proportional to the velocity of the water, and with a calibration tied to the pipe size, that rotational speed is converted into a flow rate like GPM. It’s popular because it’s robust, relatively simple to read, and works directly in the stream without needing extensive piping alterations.

A spring probe is a spring-loaded sensor inserted into the stream. The flow moves the probe and deflects the spring by an amount related to the velocity, which can be translated into a flow rate. This setup provides a direct in-stream reading and is useful when a quick, portable measurement is needed.

The other options describe devices that serve valve indication or pump control rather than measuring flow, such as indicating valve position or regulating pump output, not directly providing a flow reading. That’s why paddlewheel and spring probe are the typical flow meters you’ll see listed in fire service descriptions.