(page 3-932)TM 5-3895-374-24-2EXPANSIONTANKThe expansion tank stores extra heat transfer fluid (oil) andpermits expansion of the oil in the system when heated.It also serves as a cold-oil seal which keeps only relatively cooloil in contact with the air. The oil expands into the tank, fromthe heater through the two-inch pipe which is extended to the topof the tank. When the oil contracts, it flows from the tank intothe heater through one-inch heat trap, which also prevents hot oilcirculation between the heater and the expansion tank. The pipeplug in the trap is a clean-out for the trap, should it everbecome clogged.OperatingOilLevelThe operating oil level as seen in the glass gauge should be highenough to permit the float switch to remain "on" when the oil iscold (low) and yet not high enough to overflow when hot (high).It is desirable to start the heater with the oil level low enoughto allow for expansion of the oil as it heats.Usually after the system is brought up to operating temperature,a level in the upper half of the expansion tank is satisfactory.
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