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4-8. Attaching Drive Arm to Torque Tube
Figure 4-4. Drive Arm to Torque Tube Connection
1. Slip drive arm over torque tube shaft; clear end of torque tube housing by
approximately 0.030 inches before securing to prevent interference.
2. To tighten the drive arm assembly onto the torque tube shaft:
a. Supporting block and shaft, tighten clamp screw until snug to shaft.
b. Still supporting block/shaft, tighten clamp screw an additional:
• Sintered: 1/3 to 1/2 turn (screw can normally turn one full revolu-
tion before breaking.)
• Slotted: 1/4 to 1/3 turn (slot in the slotted clamp block should still
be open.)
NOTICE:
For Nuclear, Seismic, and High Shock Qualified Units, perform Drive
Arm Tightness Test, per para. 4-9.
4-9. Drive Arm Tightness Test
(Nuclear, Seismic, and High Shock Qualified Units Only)
This procedure tests the drive arm to torque tube attachment for tightness, by
applying torque developed by the DPU onto a fixed drive arm. Care should be
taken to apply pressure slowly, as torque is being applied to the connection
through the torque tube drive shaft and not the torque tube itself.
With pointer at normal 0% torque tube rotation position (max. minimum scale
position or 0% on a normal 0 to 100% scale unit), adjust drive arm stop bracket
(or use alternate means) to prevent pointer from moving (stop bracket interferres
with drive arm movement). Note: On reverse acting/split range units, it will be
necessary to pressurize DPU to move pointer to max. minimum scale position,
and on suppressed units, it will be necessary to apply pressure to establish a
reference point to check for "zero" shift.
Pressurize DPU as required to full calibrated scale differential pressure (100% of
the full scale range). This achieves 8-degrees of torque tube drive shaft equiva-
lent torque onto the connection.
Observe shift in the unit "zero" following DPU depressurization (as required) and
drive arm stop bracket readjusting (to allow free movement of drive arm and
pointer). A downscale (counter-clockwise) shift in "zero" of greater than 1/2% is
indicative of drive arm slippage necessitating further clamp block tightening.
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