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

286
to the "E'Lec t.r-Lc aL" control will mechanically return the valve
to the ItServolt position through the action of the control linkage.
The by-pass valve and the locking device 47 operating
lever is maintained in the ItServol1 position by a positive detent,
and in the ItManuall1position by a non-positive detent.
when lowering from the upper unloading station, during "Manual
Mechanical" control with the control pump inoperative, the Aend
pump is moved by the opera tor I s control lever from a posi
tion slightly offset towards hoisting, t.ur ough the neutral
position, to the lowering position. As the pump passes the
neutral position, the pressure in the system will drop ~omentarily,
and will tend to permit the centering plungers to engage
and the brake to apply. However at this time the main
circuit vent is closed, which will permit the centering plungers
to engage and the brake to apply only by oil leaking from
the system. The time required for the pump to pass the neutral
posi tion will be very short in comparison to the time required
for the brake and the centering plungers to engage by leakage.
If the operator should hold the pump in the neutral POSltion
long enough to permit the centering plungers to retract and the
brake to apply, it will still be possible to shift the pump
towards lowering and compress the centering spring without
building up excessive loads on the control lever.
66. Fa i lure in the hydraul i c system. - The brake will
be applied either when operating with servo electrical, or
with servo mechanical control, in the event of rupture of the
pipe lines, as follows: Rupture of the main circuit low pressure
line 41 will vent the control pumppressure, when operating
with servo electrical power, through line 42 and check
val ve 43, and engage the brake. Rupture of the main circuit
high pressure line 23, when operating with servo electrical
power, will vent the control pump pressure through B-end check
val ve 40, and engage the brake. Rupture of any of the control
pump pressure lines will engage the brake. Whenoperating with
servo mechanical control, the rupture of any pressure lines
will engage the brake, as the brake is released by main circuit
pressure.
67. Oil filters. - The oil filters 36 are mounted in
parallel in the control pump pressure lines and are arranged
so that one filter at a time may be removed and cleaned while
the unit is operating. This is accomplished by shifting the
filter control valve 50 which cuts out one of the filters, depending
upon the direction the valve is shifted. With valve
50 in the center pOSition both filters are in the system.
68. Buffers and ou er t r au e i action. - In event of overtravel
of the car at the upper unloading station it will stop
against the upper buffers at a low rate of speed. The safety