What is the primary purpose of a compound gauge in fire apparatus?

A compound gauge is utilized primarily to indicate both pressure and vacuum. In firefighting operations, it is crucial for operators to monitor various system pressures, including the positive pressure within water supply lines and the negative pressure (vacuum) that can occur in suction lines. This is because both these readings can significantly affect the performance of the fire pump and the overall effectiveness of water delivery during fire suppression efforts.

Using a compound gauge enables operators to ensure that the fire apparatus is functioning within safe and efficient pressure ranges. When suctioning water from a source such as a draft operation, the gauge will show the vacuum level, which helps to prevent cavitation and ensure the pump maintains prime. Additionally, while the gauge is not designed for direct measurement of flow rate, temperature, or pump efficiency, the readings it provides are essential for the safe operation and management of fire apparatus systems.