OP-755 Part 2 Pages 197-401 - Personal Page of GENE SLOVER

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position to permit the safety car stop device 19 to move into
the car path. However with the door open the car will stop at
the lower unloading station even though handle 32 is held in
the starting position. The car will lower, controlled by the
lowering acceleration cam, until switch 8 is opened by the
movement of the car. This vents the system and applies the
brake. Switch 8 opens only when lowering.
54. To lower from the lower unloading station to the
loading station, the door interlockswi tches 4 and 5 must be
closed. Moving the starting lever .32 to the start position
closes switch 6 and vents the system as in the hoisting cycle.
As the car starts to lower foot valve 48 functions the same as
when lowering from the upper unloading station. However as
the A-end pumpmoves farther off center, controlled by the lowering
acceleration cam, control linkage .39opens by-pass valve
60. The car then lowers by gravity controlled by the B-end
cams which change the A-end tilt to limit the acceleration and
deceleration rates. As the pump is thus returned toward center
at the end of the cycle (by the lowering deceleration cam)
by-pass valve 60 closes and the load is taken on the foot valve.
At this stage high pressure is again pumped into line 41 to
over~ome th~ foot valve spring (as at the start of lowering).
Whenthe car trips open switch 7 the system is vented and the
brake sets. Foot valve 48 prevents the car 'from settling until
the brake has had time to apply. During this lowering cycle
the main circuit is replenished through valve 6.3 whenever
by-pass 60 is open, and the centering plungers are withdrawn
by pressure delivered through valve 64.
55. During either a hoisting or lowering cycle the hoist
may be stopped and the direction Changed by the manipulation
of control lever.31. Acceleration and deceleration are limited
by the action of a dashpot assembly 65, a unit mechanically
linked to the control lever shaft. This unit is hydraulically
independent of the rest of the system. It functions to retard
control lever movement from neutral to either hoisting or lowering
positions. This occurs through transfer of dashpot cylinder
oil from one side of piston 66 to the' other through the
small feed control valves 67, the restrictions 68 and check
valves 69. If the lever (and the piston) is moved slowly, oil
will pass freely through the feed control valves and the restrictions.
If the movement is rapid pressure causes the feed
control valves to close and prevent rapid piston displacement.
When such action occurs, pressure will drop on the area above
the feed control valve (through the res triction), which will
allow the valve to open again. A balance between the pressure
build-up and the rate of motion of the piston will be established,
by the action of valves 67 and the restrictions, to limit
the rate of travel of the control lever. Piston rate of travel
is dependent on the size bf the adjustable orifice in the re-