SECTION III. PRINCIPLES OF OPERATION

TM 55-4920-442-13&P

SECTION III. PRINCIPLES OF OPERATION

1-12. Simplified principles of operation.

a. (See figure 1-4). The boost pump (2) fluid from the aircraft through the suction return port and flowmeter (1). The

output of the boost pump is passed through the cooler (6) and the low pressure filter (7) to the suction side of the high

pressure pump (13). The boost pump pressure is controlled by the low pressure relief valve (10). The output of the high

pressure pump is passed through the high pressure check valve (20), the high pressure filter (22), the flow control valve

(24) and the pressure outlet to the aircraft. The output pressure is controlled by the high pressure relief valve (31) and a

compensator control on the high pressure pump. The output is controlled by the flow control valve (24), and regulated by

a volume control on the high pressure pump.

b. The flowmeter (1) is a transparent tube type equipped with a metal float. The flowmeter scale is calibrated for 3

to 30 gpm of hydraulic fluid at 125F. A calibration curve is mounted on the control and instrument panel access cover.

This calibration curve is used for converting flowmeter indications at various fluid temperatures.

c. The fill and bleed system can be operating in either the bleed or fill mode. In the fill or bleed mode of operation,

the fill pump motor and pump (28) are energized by the-fill pump switch. When a fill valve (30) is opened, the fill pump

draws fluid from the oil reservoir (27) and passes fluid through the fill pump filter (23), low pressure check valve (16) and

the actuated fill valve.

d. In the bleed mode of operation, when a bleed valve (4) pushbutton is depressed, fluid flows from the low pressure

filter (7) through the actuated bleed valve (4) to oil reservoir (27). The bleed valve system consists of a spring-loaded

shutoff valve and a sight gage (3). The sight gage is a transparent tube that provides a means of checking the air bleed

operation.

1-10