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

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position. This opens switch 6 and shifts valve 30 to vent the
safety car stop device and allow it to return into the path
of the car. As the unit hoLst s , the acceleration rate is controlled
by the roller 26 riding on the hoisting acceleration
cam. The hoist will continue to raise at a constant speed until
the cam roller 26 rides on the hoisting deceleration cam,
which will move valve 33 in the opposite direction, to port
control pressure to the large end of piston 35, to force the
pumpyoke towards center and decelerate the hoist at the top
of the flight. As the car reaches the upper -1inloading position,
switch 9 is opened by the car. This de-energizes solenoid 1
and allows valve 2 to shift to vent and by-pass the main circuit
and to vent the control circuit. The latter action applies
brake 15, while main circuit venting allows the center-
-ing plungers to position the pump to a position slightly offset
towards hoisting. Switch 9 is designed to close by spring
as the car is lowered. However, i tsposi tion is such that a
few inches of car downwardmovement is necessary before the
switch closes. This pre-v-ents-car oscillation at the upper unloading
station in the event the car should settle slightly
befo:re the brake applies-. Foot valve 48 has no function when
hoisting - high pressure flows freely through check valve 59.
53. To lower from the upper unloading to the lower unloading
station, the starting lever 32 is movedto close switch
6, as in the 40isting4cycle. (Refer pl. 9.) The contr611~ver
31 is moved to the lowering position until the cam roller
18 contacts - the lowering acceleration carn, which will shift
valve 33 to cause stroke - control piston 35 to move the pump
yoke towards lowering. At the start of the lowering movement
high pressure in line 41 is by-passed through check valve 40.
This prevents excessive pressure b!lild-up to blow the B-end
relief valves before brake release. As soon as the brake releases,
pressure caused by the load is delivered by the B-end
into line 55 and check valve 40 closes. This prevents main
circuit by-pass and enables oil delivery through line 41 at a
sufficient pressure to overcome the difference between the
spring setting of foot valve 48 and the pressure necessary to
hold the load from dropping. The hydraulic motor will then
rotate in a lowering direction. In this action theA-end does
not tilt so far as to permit by-pass valve 60 to open, inconsequence
oil is pumped over foot valve 48 as the car lowers
to the lower unloading position. Low pressure oil is in line
23 and the system is replenished through check valve 61. The
centering plungers are held out by pressure delivered through
check valve 62. Acceleration and deceleration of _the hoist
from the upper unloading to the lower unloading station is controlled
by the end portion of the lowering acceleration cam.
The car will lower during this part of the cycle with the upper
door open. Descending three inches enables switch 9 to
snap eLose . The starting handle should be returned to stop