(e) The tail wheel lock control valve

TM 1-1520-238-T-5 7–32 Change 1 7–7. SYSTEM DESCRIPTION (cont) 7–7 (e) The tail wheel lock control valve (fig. 7–16) is a two position three–way solenoid operated valve, controlling hydraulic pressure to the tail wheel lock actuator. The TAIL WHEEL lock control panel supplies 28 VDC from the TWHL LK circuit breaker to the valve. When the tail wheel lock switch is placed in the LOCK position, the control valve is de–energized and bypasses hydraulic fluid from the lock actuator to the return line. Spring tension overcomes hydraulic pressure, locking the tail wheel. When the tail wheel lock switch is placed in the UNLOCK position, the control valve is energized. This closes the return line and applies hydraulic pressure. Hydraulic pressure overcomes spring tension, unlocking the tail wheel. A proximity switch is activated and lights the TAIL WHEEL UNLOCK advisory indicator. The emergency hydraulic shutoff valve shuts off the flow of utility hydraulic pressure to the directional servocylinder and tail wheel lock control valve when the low level switch is activated. During normal operation, the emergency hydraulic shutoff valve is open, allowing pressure to flow from the utility manifold to the directional servocylinder and the tail wheel lock control valve. When the low level switch is actuated, a 28 VDC signal closes the emergency hydraulic shutoff valve. The fluid prevented from flowing is conserved for use by the main rotor flight control servocylinders.