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10
Section 3 Model 227A Dierential Pressure Indicator
IMPORTANT: Ensure the bezel gasket is properly oriented before placing the instru-
ment back in service. Incorrect gasket orientation will cause the instru-
ment indicator to jam, resulting in inaccurate readings.
Calibration Check
To ensure the unit calibration is within factory-set calibration tolerances,
perform the following procedure.
IMPORTANT: Review all procedures, WARNINGS/NOTICES in Appendix A BEFORE
performing this procedure.
1. Mount the instrument in an approximately level position and connect to a
standard pressure source (see Mounting, page A-5).
2. If the zero indication is incorrect, remove the bezel/lens assembly and
re-adjust as described in Zero Check/Adjustment, page 7.
3. Apply 0, 50, and 100% of full scale pressure. If the indication is within
Indicator
Calibration, page 11).
4. Reverify the zero indication is correct. If it is not, repeat step 2.
Pointer Installation and Removal
During adjustment and calibration of the unit, it may be necessary to remove
and reinstall the pointer. Use the following procedures as required.
Pointer Installation
1. Position the pointer on the movement shaft with the pointer set at zero
scale. Obtain 75% to 90% pointer hub engagement on the movement
pinion shaft. The pinion shaft must not extend through the pointer hub.
It may be necessary to enlarge the hub hole, using a tapered broach (in-
cluded in the calibration toolkit, Part No. 9A-0288-1032B).
2.
perpendicular blows to avoid bending the shaft.
3. Check the calibration of the indicator over its entire range.
4. Test the pointer for tightness by moving the pointer from the zero to the
50% position manually, and then letting the pointer return freely to zero.
If the pointer indicates a shift, tap the pointer hub to tighten it to the shaft.
Pointer Removal
The pointer is removed with a pointer puller shown in Figure 3.2. This tool is
included in the calibration toolkit, Part No. 9A-0288-1032B.
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