The simplest way to think of compressed-air foam systems, or CAFS, is as three pumps working together. There is a water pump to provide the water, a foam pump or proportioner to provide the foam concentrate and create the foam solution, and an air pump or compressor to provide the air, which when agitated into the foam solution creates bubbles. The water pump is a part of all pumping apparatus. However, the addition of the other two pumps adds complexity to the fire apparatus. These additional components must be properly maintained in order to keep the system operating smoothly and efficiently.

CAFS maintenance includes:

• Daily and weekly checks,
• Strainer service,
• Fluid and filter changes,
• Adjustments, and
• Testing.

System maintenance starts with regular checks by the driver operator. These checks may be done daily, but need to be done at least weekly. They include checking the compressor and proportioner oil levels, checking the foam level, and running the system.

The compressor oil level typically is checked through a site glass or tube on the sump or oil reservoir. Some systems may have a dipstick in place of the site glass. Proportioner oil level also is checked by a dipstick or site glass, located on the foam pump. Consult your manufacturer as to the proper fluid to add when these levels are low. Fluids used range from hydraulic fluid to automatic transmission fluid to synthetic motor oil. The foam concentrate level can be checked on the foam-level gauge; however, occasional visual checks of the tank will confirm that the gauge is operating properly.

It is very important for the system to be operated on a regular basis. This includes flowing air out of the compressor. Either a discharge or an auxiliary air port can be used. Air should flow until the system is up to normal operating temperature and the air from the discharge feels warm. The time will vary depending on ambient air temperature. While the system is warming up, it should be switched into each of its operating modes. The purpose of this procedure is to exercise the compressor and the various valves that control its operation. It also removes moisture from the system. This should be done a minimum of once a week, more often in humid environments. By consistently operating the system, problems and downtime can be reduced significantly.

Most CAFS have two strainers that require regular service. The first is the foam-concentrate strainer, which keeps debris out of the foam proportioner. The second is the water strainer that prevents debris from plugging the compressor cooler. Both strainers need to be cleaned and inspected for damage on a regular basis. The cooler-water strainer will need more frequent service when drafting, as there is a greater chance of picking up foreign material.

CAFS typically have three filters that require regular service. The first is the air filter. Like an engine air filter, it must remove dirt and debris from the incoming air to prevent internal damage. Most systems utilize a replaceable, paper-element air filter. The service interval for this type of filter depends on operating conditions. Wildland apparatus operating in dusty, off-road environments will need more-frequent attention than structural apparatus operating in a municipal setting. It may be appropriate to carry an extra filter on wildland CAFS, particularly if the apparatus is being sent on a lengthy assignment or to a remote location where a new filter may not be available.

The second filter is the hydraulic filter. This filter cleans the compressor oil as it circulates. The hydraulic oil and filter typically are changed annually. They also may need to be replaced if the compressor oil becomes contaminated with water. Water can enter the compressor's hydraulic system by condensation, through a leaking air check valve, or through a damaged heat exchanger. Refer to your manufacturer's recommendation regarding the proper fluid types and capacities.

The third filter is the air/oil separator cartridge. Its purpose is to recover all of the oil from the air before the air goes to the discharge. The typical replacement interval for the separator cartridge is biannual. This interval may need to be annual when operating in humid environments, due to the increased amount of condensation, which tends to shorten filter life. The separator cartridge may be mounted externally so that it is easy to locate, or it may be mounted internally inside the sump or oil reservoir. If you do not see a separator cartridge, do not assume that the system does not have one. Instead refer to the system manufacturer for the proper service information.

Adjustments to the system include proportioner and compressor adjustments. Proportioners must be calibrated to function accurately. Compressors must be adjusted to provide the proper pressure in various operating modes.

Proportioner calibration methods and requirements vary between the different manufacturers. Most require calibration of the water flow and some also will require calibration of the foam-concentrate flow. To calibrate the water flow, enter the calibration mode and then flow a known volume of water through a foam-capable discharge. Once that's done, then calibrate the proportioner by telling it how much you are flowing. It is best to calibrate at a flow that typically is used on the fire ground. This is because the flow rate at which the calibration was done will be the most accurate.

For example, wildland apparatus would be calibrated in lower flow ranges, while structural apparatus would be calibrated in higher flow ranges, as this is where they normally operate. To calibrate the foam flow, enter the calibration mode and then flow a known volume of foam concentrate into a graduated container. Then, tell the proportioner how much you flowed. Be sure to use the proper procedure in order to save all of the calibration settings.

Pressure adjustments on the compressor include the maximum compressor pressure and the air/water pressure balance. Maximum air pressure typically is set around 150 psi. It is set by adjusting a fixed pressure regulator in the system. If this pressure is set too low, there will be insufficient pressure to make CAF through all operating ranges. If the pressure is too high, it potentially could cause safety issues stemming from excessive energy in the hose line. Balance between the air and water pressures usually is done using trim valves in the air-control circuit. This balance is important in order to assure that both air and foam solution will enter the hose line in the proper proportions. Refer to your specific manufacturer as to their recommended adjustments and procedures.

Compressor systems should be tested annually, as are fire pumps. During the annual pump test is a good time to test the compressor. The test is conducted by running the compressor and flowing air at its maximum-rated CFM output at 125 psi. The test is run for twenty minutes. The air-flow CFM can be measured with a calibrated flow meter or through a fixed orifice at a specific pressure. Air-flow and compressor-temperature readings are taken at the start, and then at five-minute intervals throughout the test. During the test, the air-to-water-pressure balance should be checked at both 100 psi and 125 psi.

As with other components of modern fire apparatus, CAFS will provide long, trouble-free service when properly maintained.

• Read the "Class A Delivery" sidebar to learn about high-pressure foam systems.

Keith Klassen has nearly 35 years of experience in the fire service, both as a volunteer and as a career firefighter. He is currently a captain for Summit Fire Department in Flagstaff, Ariz. Klassen also is the CAFS instruction program manager for Waterous Co.

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