Ventilation equipment that fails to perform properly may jeopardize the health or life of crew members. Therefore, the individuals responsible for inspection and maintenance must be thoroughly familiar with the common hazards that can prevent normal operation of ventilation equipment.

GUARDING AGAINST OBSTRUCTIONS TO VENTILATION

Items such as swabs, deck cleaning gear, and trash stowed in fan rooms or ventilation trunks restrict airflow and increase dirt and odors taken inboard. Ventilation terminals must NEVER be used for stowage. Wet clothing secured to ventilation terminals increases the moisture content of the compartment air and restricts airflow. Stowage arrangements should be such that weather openings for a ventilation system are NEVER restricted.

KEEPING THE SYSTEM CLEAN

Dirt accumulation in a ventilation system restricts airflow and creates a serious fire hazard. In a clean duct, the cooling effect of the metal tends to act as a flame arrester, but an accumulation of foreign matter within a duct is a potential source of combustion. One method of reducing the amount of dirt and combustible matter which may be carried into a ventilation system is to wet down the deck areas near the air intakes before sweeping.

Since a large volume of air passes through or over the elements of a ventilation system, dirt collects in various units in spite of all pre-cautionary measures. Therefore, periodic inspec-tions and consistent regular service procedures are necessary to keep the system clean. Filters help keep ventilation systems free of dust and dirt. Navy standard air filters have pressure taps on each side of the filter bank. By using a portable differential pressure gauge, you can quickly read the pressure drop across the filter. When the pressure drop increases to three times that of a clean filter, replace the filter. Ships carry spare filters so that a clean one may be substituted for the dirty one.

Special cleaning sinks are installed in ships with enough filters to justify the space, expense, and weight. These sinks are either of two types- steam or ultrasonic. In the steam type, steam is used to heat and agitate the water. In the ultrasonic type, cleaning is done by vibration caused by sound waves passing through the clean-ing fluid.

Navy standard air filters have a thin film of oil applied to the wires. The oil film retains fine particles of dust and lint. After they are washed, the filters should be reoiled by spraying with filter oil. Sprayers furnished for oiling air filters must NOT be used for any other purpose. This precaution is to prevent contamination of the filters with toxic, flammable, or smelly materials. Flame arresters and grease filters should never be oiled.

SUMMARY

In this chapter, we have presented general information on the principles, equipment, and processes of air conditioning as these factors pertain to the ventilating, cooling, and heating of a ships living and working spaces. Detailed information concerning the operation and maintenance of air-conditioning equipment may be found in the Naval Ships Technical Manual, chapters 510 and 516.

You should have a basic understanding of the use of a psychrometric chart, which shows the relationship between the dry-bulb temperature, the wet-bulb temperature, and the dew point. These concepts are important in the operation and maintenance of air-conditioning equipment. In addition, you should recognize the general arrangement of air duct systems; how ventilation systems are adapted to various compartments of your ship; and how the various types of cooling and heating systems are used.

For efficient operation of air-conditioning and ventilation systems, you should strictly follow PMS requirements of the 3-M Systems and the specified technical manuals for your equipment. If you have any questions concerning the material in this chapter, we recommend you reread the sections with which you are having difficulties before continuing to chapter 18.