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DRY-AIR SYSTEMS Some radars depend on inputs of dry air for proper operation. Radar dry air is normally supplied by the ship's central dry-air system. This system produces high-pressure (hp) air and low-pressure (lp) dry air for distribution to user equipment, such as a search or a fire control radar. Electronics Dry-Air Branch The electronics dry-air branch is fed from the vital service lp air main through the Type II (desiccant) or Type III (combination refrigerant and desiccant) dehydrators, as shown in figure 4-12. The purpose of the electronics dry-air branch is to provide several electronic equipments with air that is dry enough for proper operation. Microwave components, such as waveguides, cavities, and power amplifiers, require dry air to prevent arcing and internal corrosion. The electronics dry-air branch must satisfy the dry-air requirements of the electronic user equipment. Dry air of less than the required specifications will degrade equipment performance. It may also incur major repairs, overhaul, or replacement of expensive electronic components. Figure 4-12. - Typical lp air system layout.
Air Control Panel The dry-air distribution system (figure 4-12) delivers dry air to each air control panel of the user equipment. The air control panels are used to control and regulate the dry-air pressure to that required by the electronic user equipment. The air control panel (figure 4-13) provides a means of monitoring the dry-air supply to the user equipment. The type of control panel used varies, depending on the outlet pressure and flow rate required. Figure 4-13. - Air control panel flow diagram.
The dew point (related to moisture content) and the flow of the lp dry air can be monitored at the air control panel. Also, the dry-air pressure can be monitored at the input to the control panel, at the input to the flowmeter (in which accuracy is calibrated at a certain pressure), and at the output of the control panel. A filter is installed to trap particles that affect proper pressure regulation. A metering valve bypass and a pressure relief valve are provided in case of malfunctions. The metering valve bypass permits manual control of air pressure to the user equipment. Electronic Equipment Dehydrators. Dehydrators or compressor-dehydrators are supplied as part of various radars. Many of them were provided prior to installation of properly configured central dry-air systems. These dehydrators are intended for emergency use in the event of the failure of the central dry-air system. In a typical configuration (figure 4-14), the outlet air from the local dehydrator is connected between the air control panel outlet and the user equipment or radar by a three-way valve. Figure 4-14. - Typical local dehydrator interface.
Local dehydrators depend on the ship's lp air for an inlet supply, while the local compressor-dehydrators can operate independently of the ship's air supply. Some units of electronic equipment that have local dehydrator units are pressure interlocked within the dehydrator unit. When the outlet air pressure is below a set value, the interlock prevents the equipment from going to a full OPERATE condition. When the central dry-air system is used, the pressure interlock is bypassed. Some radars provide a tank of nitrogen as an emergency source that can be connected in place of dry air. Special safety precautions must be taken when you handle compressed gases because of the possibility of explosion. Nitrogen does not support life; when released in a confined space, it can cause asphyxiation. Q.16 What is the normal source of dry air for a radar system? |
 
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