Protective Devices and Instrumentation

TM 55-4920-442-13&P

Protective Devices and Instrumentation (Refer to figures 1-3 and 1-4).

a. A thermal relief valve limits pressure in the low pressure section caused by thermal expansion of fluid.

b. A thermoswitch in the high pressure pump inlet circuit actuates to shut down the unit when the fluid temperature

reaches 165 5F.

c. Low pressure switches protect the high pressure pumps against cavitation due to low inlet pressure or boost pump

failure. If the pressure drops below 40 5 psig, the automatic shutdown of the unit is executed automatically.

d. Check valves prevent reverse flow to the fill pump system.

e. Differential pressure switches across filter ports of the high pressure filter illuminate red warning light on control

panel to indicate a clogged filter element.

f. Circuit breakers are provided for overload protection of various circuits. Refer to figure C-7 for location of

electrical components and figure 1-3 for wiring schematic.

g. Complete instrumentation and controls are located on the control panels. Refer to Section IV. for description of

function and location.

Electrical system. (see figure 1-3). The system provides the circuits and control for proper functioning of electrical

components.

a. Electrical power is supplied by an external source through No. AWG 00 4/c extra flexible cable, 50 ft. long.

b. The fill pump motor is controlled by a switch on the control panel and a circuit breaker in the electrical

components panel.

c. A time delay relay (1TR) is actuated when the start pushbutton (2PB) is depressed to allow a 1 second delay for

pressure build-up.

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