A-27
Model 199 Differential Pressure Unit (DPU) Section 4
Drive Arm Tightness Test
This procedure tests the tightness of the drive arm's connection to the torque
tube by applying torque developed by the DPU onto a xed drive arm. Care
should be taken to apply pressure slowly, as torque is being applied to the
connection through the torque tube drive shaft.
1. With the pointer at normal 0% torque tube rotation position (0% on a
normal 0 to 100% scale unit), adjust the drive arm stop bracket (or use
alternate means) to prevent the pointer from moving (stop bracket inter-
feres with drive arm movement).
IMPORTANT: On reverse acting/split range units, it will be necessary to pressurize
the DPU to move the pointer to the minimum scale position, and on
suppressed units, it will be necessary to apply pressure to establish a
reference point to check for "zero" shift.
2. Pressurize the DPU to full calibrated scale DP (100% of full scale range)
to apply 8 degrees of torque tube equivalent torque to the connection.
3. Observe the 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). If the "zero" shifts counter-clockwise more
than 1/2%, tighten the clamp block to prevent drive arm slippage.
Adjusting Pulsation Dampener
Reference Figure 6.1, page A-35, for the location of the pulsation dampener valve.
1. Remove the dust cover and insert a 1/8-in. hex key into the needle valve.
2. Turn the valve clockwise to the closed position, approximately 3 turns.
3. Back out the valve 1/2 turn or as required to reduce pulsations/shock
pressures.
Troubleshooting
See Table 4.3, page A-28, and refer to actuated instrument manual for more infor-
mation.
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