Air quality

The third area that departments must consider when specifying CAFS is the air system. The air system’s main component includes the air compressor and drive systems, air-to-water pressure balancing system, and air delivery devices including air and check valves.

Typical apparatus-mounted CAF systems use a compressor rated anywhere from 80- to 200cfm. These compressors typically have four different drive options: pto-driven, pump-driven, hydraulically driven or auxiliary engine–driven.

A PTO-driven compressor may provide the department with some additional operational options, but its main benefit is that it allows the department to run the compressor without running the fire pump. This can be useful if the unit needs to supply large quantities of air for needs outside of the standard caf firefighting operations. PTO-driven compressors also frequently are used in retrofitting in-service apparatus with CAF systems. PTO-driven compressors also may provide apparatus builders with additional mounting locations and options for apparatus that are short on pump compartment space.

A typical pump-driven compressor receives its power through the pump. This is both a benefit and a drawback, as it reduces the chances of the compressor overheating, but it also means the compressor is only powered if the fire pump is engaged and turning. Another benefit to the pump-driven compressor is that the complete package is mounted in the pump compartment — fully assembled, tested and calibrated by the pump manufacturer. These systems are cost-effective and simple to install for the apparatus manufacturer; however, it also may require additional space in the pump compartment.

Both the PTO-driven and pump-driven compressors can be equipped with auto-on features, which allow the compressor to come on line and be operational any time the pump is placed in gear. If the operation calls for a non-CAF mode, the operator simply disengages the compressor and proceeds with a water only or foam solution mode. Benefits to this include one less step for the pump operator, reducing the chance that a key step will be forgotten or missed. Drawbacks include possible unnecessary running time on the compressor.

For a hydraulic-driven compressor, a hydraulic pump is driven off a transmission PTO. Hydraulic fluid then is used to operate a hydraulic motor, which drives the compressor. The benefit is that the compressor can be mounted wherever space is available and hydraulic lines run to it. The downside is the additional cost and complexity of the hydraulic-drive system. The auxiliary engine–driven compressor has a separate engine that powers both the water pump and compressor. The benefit is the option of true pump-and-roll capabilities because the caf system isn’t connected to the truck powertrain. The downside is increased cost and weight, the spaced needed for the system, and the maintenance of a second engine.