Page 246 - Reciprocating Compressors Operation Maintenance

Overhaul and Repair of Reciprocating Compressors 231

Fortunately, we can employ one of several methods to check the align-
ment of the compressor crankshaft system and the relationship of the
compressor cylinders to the frame. When foundation or grout failure
occurs, more serious distress may follow. The compressor crankcase or
frame takes on a new alignment pattern because the foundation no longer
furnishes precise support.

Web deflection measurements are thus required for determining devia-
tions in the crankshafts of large industrial/marine engines and reciprocat-
ing compressors. These measurements and their interpretation are vital in
disclosing conditions that can lead to disastrous and expensive crankshaft
failures. Accurate periodic measurements, combined with careful analysis,
will permit such conditions to be corrected before they cause problems.
Web deflection is defined as any movement of the crank webs from
their ideal position during the entire rotation of the crankshaft (360°).
Consider the crankshaft in Figure 4-2, whose centerline, perhaps because

B

0-DEGREE CRANK ANGLE

A

180-DEGREE CRANK ANGLE

FIGURE 4-2. Crankshaft deflection mode.

Contributed by Jim McNabb (Southern California Gas) and Leon Wilde
(Indikon Company, Inc., Somerville, Massachusetts).