What is the purpose of bleeders in fire apparatus engineering?

The purpose of bleeders in fire apparatus engineering is primarily to bleed air off as the supply line is charged. When a fire pump is brought online, it is crucial to ensure that air is removed from the water supply lines. Air trapped in the system can lead to a phenomenon known as "water hammer," which can damage the pump and piping system. By using bleeder valves, firefighters can release this trapped air, allowing water to fill the lines completely and ensuring the pump operates efficiently.

Maintaining pump pressure and preventing backflow of water are also important aspects of fire pump operation, but they are not the specific function of bleeders. Regulating water temperature is unrelated to the function of bleeders and pertains more to the cooling systems or thermal management in various contexts. Thus, the primary role of bleeder valves is indeed to facilitate the charging of supply lines by expelling trapped air.