What device is used to indicate flow in gallons per minute?

The device used to indicate flow in gallons per minute is a flowmeter. Flowmeters are designed specifically to measure the flow rate of fluids, including water, which is critical in firefighting operations to understand how much water is being delivered through hoses and nozzles. This information helps firefighters to determine how effectively they can suppress a fire and manage resources.

Flowmeters can provide real-time feedback on flow rates, ensuring that operators can make informed decisions regarding water supply and pressure management. This is crucial in emergency situations where precise water delivery can significantly impact firefighting efforts.

The other devices listed serve different purposes: a pressure regulator is used to control and maintain pressure in a system; a hydraulic jack is used for lifting heavy objects and does not measure fluid flow; and a transfer valve is employed to redirect the flow of water but does not measure it. Hence, the flowmeter is the only choice that accurately indicates flow in gallons per minute.