CAF System Components

CAF systems seem complicated to some people. There are a lot of little components. But most of the components exist to allow the system to produce high volume CAF for as long as needed. Some of the components exist to make the foam automatically while some components exist to keep the high-volume system cool and functioning. Understanding each component and its roll in CAF delivery will help firefighters understand the system and help the system last for years to come. Just remember the entire process is based on W + Conc + A + A = Foam (Bubbles).

The components are separated into four sections: Compressor, Hydraulic Oil System Components, Air Control Circuit Components, and Misc. Components (the parts that do not fit directly into the previous categories? The four categories are found in the drop down menu.

For the location of and relation to the various components, please reference the below diagram.

Air /Oil Separator

The AOS is the 2nd stage in the separation of compressed air from the hydraulic oil (the first being the sump). While it looks like a larger oil filter, the cannister’s function is to filter out the hydraulic oil mist in the compressed air and return the oil to the compressor while the compressed air …

Air Gauge

CAF systems have two pressure gauges on the pump panel. One for water pressure, and one for air pressure. The air pressure gauge allows the operator to monitor the air pressure for the different operational modes. An additional option is a double gauge whereby the air & water are attached to one gauge that incorporates …

Air Inlet Valve (AIV)

The AIV is mounted on the inlet to the air compressor. It serves as the throttle controlling the compressor discharge pressure. Unlike the throttle on an engine which is an adjustable stationary valve the AIV is a modulating valve which is constantly opening and closing. It controls the air entering the compressor. More air allowed …

Air Manifold

The air manifold is a manifold that takes in air coming from the MPV and distributes the air to the individual discharge outlet valves where the air will mix with the solution heading into the fire hose to agitate and form CAF.

Air Only Outlet

Some CAF systems are equipped with an air only outlet, generally mounted on or near the pump panel. This outlet is useful for air only needs where foam solution would be undesirable. This outlet can be used to air up tires, recharge extinguishers, other air tools, or just as an air blower for cleaning air …

Alarm System

Large CAF systems are equipped with red light and beep sounds if the hydraulic oil temperature gets too high. The alarms are set (generally at 250° F) to sound in time for the operator to either correct the high heat issue or to place the system in unload mode before the system suffers damage. Failure …

Auto Sync System (Air Control Circuit)

The auto sync system is the operator-controlled portion of the air control circuit. The auto sync system can have either manual or electric switches that direct pressurized air to control the CAF system modes. The operator-controlled modes are: Unload Mode – whereby no air is requested for compression. (used for NAF or flushing). Auto/Run Mode …

Check Valves – Water & Air

There are two areas where you will find water check valves. The first is in the plumbing from the pump, just after the pump-to-tank recirculation valve and just before the foam concentrate injection port just ahead of the foam manifold. This check valve prevents foam concentrate from backing into the pump-to-tank recirculation valve resulting in …

Compressor

The air compressor on a CAF system might be a screw type or a piston type depending on the desired capacity. Larger systems use screw compressors. Compressors are designed simply to compress air. Keep in mind that compression generates heat. Therefore, all compressor systems will incorporate some form of cooling method

Foam Manifold

The foam manifold is a rectangular or round cylinder (vertical or horizontal) where the water and foam concentrate mix. The foam concentrate inject point occurs in the plumbing from the pump just prior to entering the foam manifold. From the manifold, plumping heads to each individual solution discharge.

Foam Tank

A Foam tank is a very desirable add on for any engine incorporating a foam concentrate proportioning system. A properly designed, built, and maintained foam concentrate storage tank has several components as required by NFPA: 1) alockdown, sealable lid with a vent valve; 2) an electronic floating trip switch to signal a concentrate proportioning system …

Heat Exchanger

Air compression generates heat. The heat exchanger is utilized to keep the hydraulic oil cool. Hydraulic is combustible and must remain well below its ignition temperature. There are several types of heat exchangers in use. The first, a Shell & Tube is a cylinder-shaped device. Inside the cylinder is a coiled copper water line. The …

Hydraulic Oil Temperature Gauge

This gauge is a great indicator that the system is functioning normal or not. Air compression causes heat. The heat exchanger cools the heat. If the temperature gauge is registering hotter than normal during operations, immediately begin a system diagnosis to identify the problem. Did the water tank run out of water? Is the clean …

Minimum Pressure Valve (MPV)

The MPV is a spring-loaded device just downline form the AOS. The MPV is factory set usually at around 30-40 psi. The system will use this minimum pressure to push the hydraulic oil through the compressor lubricating and cooling system. At minimum pressure, there is no air available to mix with the solution in the …

Pilot Balance Valve (PBV)

Prior to the early 1990’s, to make CAF work, the pump and compressor each had to have a separate engine driver. The Solution (W + Con) and air (+A) must be equal for both to enter the discharge hose (+A – Agitation) to make foam. As the system would fluctuate, one pressure would go higher …

Site Glass

The site glass is mounted on the Sump and gives a view into the sump to check the level of the hydraulic oil. It is recommended that the hydraulic oil level be maintained 1.2 way across the site glass. The oil level can drop (system use, torn AOS, frozen heat exchanger, etc.), or increase if …

Sump

The Sump has two primary fuctions. The first, is the storage tank for the compressor hydraulic oil. The 2nd, is the first of 2 stages in the separation of the hot hydraulic oil and hot compressed air. The opposing screws type compressor requires hydraulic oil to keep the screws turning. As air is pulled in …

Water Line Clean Out Trap (Wye Strainer)

Covered in detail on the How NOT to Destroy a CAF System Page. To keep debris passing through the fire pump from circulating and possible plugging the small water lines of the heat exchanger, a clean out wye strainer or pump panel mounted basket strainer is added with a collector screen to catch such debris. …