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

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tank, to permit manual shifting of piston 35. The main circuit
lines 41 and 23 are not supercharged, but the system leakage
is replenished by suction through the replenishing check
valves 45.
64. Limitations) manual control. - When operating the
hoist using "Manual Mechanical" control, the manual shifting
of the pump yoke 20 greatly increases the effort required on
the opera tor I s hoist and lower control lever 31 to shift the
pump off center, and in the same manner greatly increases the
loads on the cam mechanism and linkage to return the pump yoke
20 to its center position. This loaded condition in conjunction
with stopping on the latch and vent valve 54, and the
stretching of the hoisting cable greatly increases the stopping
variation at the loading arid unloading stations. The
main circuit lines 23 and 41 will not be supercharged, which
will result in cavitation in the system, and will cause gasification
of the oil in the system to increase the noise and
vibration if the equipment is operated at high speeds. If continuous
high speed operation is attempted, the oil may become
so gasified as to prevent proper operation of the brake, and
also will cause very slow starting of the hoist.
65. Operation with manual control. - In order to obtain
as accurate stopping as possible and to obtain the least
amount of noise and vibration for continuous operation, it
will be necessary to operate the hoist at much slower speeds
than when using !lServo Electrical" or "Servo Mechanical" control.
This is accomplished by moving the hoist and lower control
lever 31 only partially towards the hoisting and lowering
positions. For the most satisfactory operation using "Manual
Mechanical" control it is recommended that the cycle time be
increased to 12 to 15 seconds for hoisting and 10 to 12 seconds
for lowering. This method of operation should be considered
as an emergency condition due to malfunctioning of the
control pump, which should be corrected as soon as possible
after its failure.
In order to permit training of the ship I s personnel in this
method of operation, a control pump by-pass valve has been
provided, whose only function is to by-pass the control pressure
to the tank to simula te a control pumpfailure. This valve
is actuated by the same lever which shifts the servo valve
locking device 47, when the lever is shifted to the "Manual"
position. This valve cannot be shifted inadvertently to the
"Manual" position if the control selector lever 12 is in the
"Electrical" control position. This is prevented by linkage,
which permits the shifting of the valve only when the control
selector lever 12 is in the "Mechanical" control position.
If the valve has been shifted to the "Hanua l.'' position, the
moving of the control selector lever 12 from the TlMechanical"