EXPANSION TANK

EXPANSION TANK The expansion tank serves a threefold purpose in a liquid cooling system. First, it maintains a positive pressure required on the circulating pump inlet for proper operation of the circulating pump. Second, the expansion tank compensates for changes in the coolant volume because of temperature changes. Third, it vents air from the system and provides a source of makeup coolant to compensate for minor losses because of leakage or losses that occur during the replacement of radar equipment served by the system. The tank maybe either a gravity tank or a pressurized tank. When an expansion tank is used as a gravity tank (fig. 1-11), it is located above the highest point in the distilled water system. This provides sufficient pressure to the suction side of the circulating pump. This also ensures a flow of water from the tank into the system when makeup water is required. The tank is provided with a sight glass to check the level of water in the tank. The sight glass should normally show the tank to be two-thirds to Figure 1-11.-Gravity expansion tank. four-fifths full. The glass should be redlined at four-fifths of the tank capacity. A vent pipe is located on the top of the tank to prevent air pressure from building up in the system. A valve and funnel connection with cap is located on the top of the tank to provide a means for filling the system with distilled water. A low-level alarm switch is usually set at 20 percent of tank capacity. When the fluid level in the tank lowers to 20 percent of the full level, visual and audible alarms actuate at the alarm switchboard to warn personnel when the system is low on distilled water. If the tank should run out of water, then air is drawn into the system, which results in increased corrective maintenance on the system to remove the trapped air or possible pump damage and/or failure of high power transmitter components. The pressurized expansion tank (fig. 1-12) is normally located near the circulating pump suction in the return main of the secondary liquid cooling system. The pressurized tank is airtight and is charged with compressed air to an appropriate pressure from the ship’s low-pressure air system. In some systems, a hose Figure 1-12.—Pre-ssure expansion tank. 1-10