The hydraulic-mechanical actions that extend the A-side center guide begin when solenoid LCGA(B)l energizes (fig. 4-24). The detente mechanism is released and UVGA(B)12 shifts to the right. This pivots the rocker arm which shifts UVGA(B)11 to the left. The detente mechanism reengages. At this point, the interlock control circuit has done its job and, in effect, is no longer needed. The remaining actions are all strictly hydraulic and mechanical.

When solenoid valve UVGA(B)11 shifts left, it connects PA on the left end of the directional valve UVGA(B)22 to the tank. By bleeding this fluid pressure to the tank, the directional valve is free to be shitfed. When solenoid valve UVGA(B)12 shifts right, PA is connected to the right end of UVGA(B)22. This fluid pressure causes the directional valve to shift to the left. It is very common to see solenoid valves control a directional valve in this manner. By itself, the solenoid assembly cannot handle the volume requirements of the system, primarily due to its small size. By controlling a larger directional valve, the volume requirements of the system are satisfied.

The speed at which the directional valve UVGA(B)22 can shift is regulated by the two orifices in the end chamber lines. They are installed to prevent a sudden shock to the cylinder. As UVGA(B)22 shifts, it connects PA to the top (or extend) side of the cylinder. It also connects the bottom (or retract) side of the cylinder to the tank.

As PA enters the cylinder, the piston (UCGA(B)4) moves down. This extends the center guide into alignment with the front guide. The piston is tapered at its ends. As it nears the bottom of the cylinder, it gradually closes the tank port and buffs to a smooth stop. The check valves at the top of the cylinder permit a rapid, but controlled, acceleration of the piston. The check valves in the bottom of the cylinder assist in the buffering action as the piston nears the end of its stroke.

To complete the extend cycle, the arm on the switchrod has now actuated interlock switch SIGA(B)19. The switch sends an electrical signal to the coil of control relay (center guide extended) and energizes it. They open and solenoid LCGA(B)l de-energizes.

RETRACT CENTER GUIDE OPERATION

The hydraulic-mechanical operations that retract the center guide begin with energizing LCGA(B)2 (fig. 4-25). They basically reverse the extend cycle actions. We will not go into a detailed explanation of this operation. Study and compare the extend and retract hydraulic schematics and you will see the differences. Retract time is 1.17 seconds.

The GMLS center guide hydraulic-mechanical operation was relatively simple. A piston within a hydraulic cylinder was made to move. Fluid power was converted into a mechanical linear motion. Different hydraulic actuators may convert this fluid power into a rotary type of motion. However, the hydraulic answer source is still the same-an accumulator type of power drive.