Page 251 - Reciprocating Compressors Operation Maintenance

236 Reciprocating Compressors: Operation and Maintenance

* Needle on dial face moves with ease. There should be no needle
movement "hang-up" or drag after preloading the gauge, approxi-
mately one to one and one-half revolutions.
* Needle points on instrument and all extensions are sharp and crisp
so as to correctly fit the web punch marks.
* The dial face must remain visible to the observer throughout the
entire crankshaft rotation.
b. Irtdikon Electronic Web Deflection Indicator
As shown in Figure 4-6, this system consists of two units: a mea-
suring head and a digital indicating instrument. After selecting the
proper extensions, place the measuring head between punch marks.
Then take the following steps:
* Move the threaded adjustment to obtain the proper preload. Red
and yellow lamps on the measuring head indicate the required
direction of adjustment. When both lamps are out, the adjustment
is correct and the transducer is within its measuring range.
* Attach the magnets at the center points to the adjacent web. This
drives the centers in synchronism with the crankshaft as it is rotat-
ed, preventing the center points from rotating or "squirming" in
the punch marks. Inaccuracies are thus minimized if the punch
marks are not perfect.
* Because one magnet also drives the angle transducer, position it so
that the correct starting angle is obtained (usually 0° and in the
direction the crank is rotated when operating).
* Verify that the counterweight hangs freely to assure correct angle
readings.
Once the measuring head has been placed in position, readings of
both web deflection and crank angle may be taken from the digital
indicator.
Checking for proper operation is easily accomplished before use.
For deflections, move the measuring plunger inward by hand while
observing the change in distance readings. For angle, rotate the
transducer magnet and observe the readings.
A rigid calibration stand is essential because the relatively large
seating force (approximately 5 pounds) can cause spurious deflections
in conventional outside micrometers. A complete calibration stand, or
fabrication drawings for one, may be obtained from the manufacturer.
4. User skills
It is important to ascertain that the engineer, technician, or
mechanic is skilled in web deflection measurement procedures and