IBM 727, Manual Of Instruction, Page: 17 / 163

At the bottom of each vacuum column, separating the column from the manifold,
is a flapper valve. This valve is sim ilar to a door, held open under spring tension.
A rush of air down the column strikes the flapper valve and closes it. Thus, the
flapper valve and its associated m icroswitch, give an indication as to whether tape is
in the vacuum column. When tape is in the column, very little air passes down the
column and spring tension pulls the flapper valve open. When tape is removed from
the column, or is broken, the rush of air downward closes the flapper valve and its
m icroswitch.
Adjustments of all. the switches associated with the vacuum columns are covered
under "Removal, Assembly and Adjustment P ro ced u res."
4. 7 MOTOR DRIVE
The reel drive clutches are driven by two 1/4 HP, 30, 220v, AC m otors (1140
RPM), one providing forward motion and the other providing reverse motion. Fig­
ure 12 is a front view of the drive motor and pulley arrangement.
The forward drive motor is located in the lower right-hand corner and is con­
nected to the two center clutches by two V-belts adjacent to each other.
The reverse motor is located in the lower left-hand corner and is connected to
the two rear clutches in the same manner as the forward m otor.
To provide very fast motion of the reels during high-speed rewind, an additional
motor (1/12 HP, 30, 208v, AC, 3450 RPM) is provided in the upper left hand corner.
This motor is coupled to the file reel shaft and during normal tape motion is m erely
turned with the file reel shaft. However, when the machine goes into a high-speed
operation, this motor drives the file reel shaft at a high rate of speed. At this time,
none of the magnetic clutches are energized.
The capstans are driven by a 1/10 HP, 30, 220v, AC motor running at 1300 RPM.
This motor is turned off when the capstans are retracted.
4 .8 TIME DELAY
The time delay and its drive motor are located on the relay gate. This mecha­
nism delays machine operation at the end of a high-speed rewind to allow the reels
time to stop before tape is loaded into the columns. When the motor starts running,
it drives an operating arm by means of a reduction gear train. After a given time the
arm operates a m icroswitch, referred to as the time delay point. As long as power
remains on the m otor, the operating arm holds the time delay point closed. When
power is rem oved, the arm returns to a home position under spring tension. The
length of the time delay can be set with a calibrated dial on the front of the assembly.
4. 9 CAPSTAN RETRACTING MECHANISM
While unloaded and while high-speed rewinding, the drive capstans must be r e ­
tracted to allow free passage of the tape past the read-write head area. This opera­
tion is accomplished with a linkage operated by a solenoid at the right of the machine
(Figure 13).
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