Figure 6-6-9. Sequence Valve Operation

TM-1-1520-240-10 Army CH-47D Heilcopter (EIC:RCD) Manual
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TM 1-1520-240-10 6-6-16 CAUTION Do not press the sequence valve plunger unless the ramp is down. 6-6-24. Ramp Control Sequence Valve. A mechanically operated sequence valve controls the sequence of the cargo door and ramp operation (fig. 6-6-9). The valve is below the ramp control valve at the ramp hinge line. A plunger on the top of the valve is manually pressed to hold the cargo door at full open during ramp operation. The plunger can be locked in the depressed position by rotating a retainer pin which ex- tends from the side of the valve. 6-6-25. Pressure Actuated VAlve. Ramp operation is stopped during cargo door operation by a hydraulic pressure actuated valve. The valve is locked near the ramp control valve (fig. 6-6-8). A plunger provides manual override of the valve if it sticks. 6-6-26. Accumulator Gage. A gage at station 534, right side indicates APU accumu- lator pressure in psi (fig. 6-6-8). A pressure reading on the accumulator gage in excess of 2,500 psi is sufficient for operating the ramp. 6-6-27. Equipment Loading and Unloading. The following procedures should be observed in prepar- ing the helicopter for cargo transport mission: a. Doors — Open. b. Parking brake — ON. c. Troop seats — Stow. d. Cargo compartment — Clean. e. Tiedown devises — Check, for type and quanti- ty. f. 10,000 lb tiedown fittings — Install as required. g. Loading aids — Check, for condition and opera- tion. h. Weight and balance data — Check. i. Emergency equipment — Check. j. Emergency exits — Inspect. k. Cargo load — Inspect. 6-6-28. Ramp Operation. 6-6-29. Normal Operation. WARNING When the RAMP PWR switch is OFF, be sure the RAMP CONTROL VALVE remains at STOP. If the RAMP CONTROL VALVE is moved to UP or DN, the ramp may free fall. 1. Lower the ramp as follows: a. RAMP PWR switch — ON. NOTE Perform step b. and c. only if the ramp is low- ered with accumulator pressure. b. APU accumulator gage — Check 2,500 psi or more. If pressure reading is below 2,500 psi, operate the hand pump to build up pressure. c. EMERG UTIL PRESS valve — Open. Figure 6-6-9. Sequence Valve Operation

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