TM 1-1500-204-23-2
Figure 4-124. Radial Cam-Operated Selector Valve
down side of the landing gear actuating cylinder, thus extending the gear. Return fluid from the door actuating cylinder is
routed to the reservoir through sequence valve. A while the landing gear is still retracted and the sequence valve is still
open.
(2)
Pressure-actuated sequence valves. The typical pressure-actuated sequence valve consists of a
three-port housing, a spool-type valving device, and an adjustable spring. Operation of the pressure-actuated sequence
valve shown in figure 4-130 is dependent upon movement of the spring-loaded spool. Unlike the mechanically-operated
type, no mechanical contact with any other unit is necessary to operate a pressure actuated sequence valve. When the
selector valve is positioned, fluid pressure is directed to the pressure inlet port of the sequence valve and passes through
the valve to the first unit to be actuated. The pressure necessary to operate this unit is less than that required to move
the spool against the restraint of its spring. After operation of the first unit is completed and flow to it ceases, pressure in
the passage between the pressure inlet port and the first unit port increases. This pressure is conducted through a
special passage to the underside of the pilot piston on the lower end of the spool, forcing the spool upward until the
passage between the pressure inlet port and the port to the second unit becomes unblocked. Fluid then flows into the
second unit, causing it to operate.
Figure 4-125. Solenoid-Actuated Control Valve (Energized)
4-130
