Page 380 - Reciprocating Compressors Operation Maintenance

Preventive Maintenance for Reciprocating Compressors 365

the acceleration level increased to over 6 g's, which caused alarms to
actuate in the remotely-located control room.
The company's vibration specialists were called in to help analyze and
determine the extent of the problem. They quickly determined that the
acceleration level changed from approximately 5.5 to 7.8 g's, depending
on the load. This increase was unusual. An oscilloscope was then con-
nected to the buffered transducer output of the dual accelerometer moni-
tor. By observing the timebase waveform, plant personnel had a clear
picture of what was being observed by the accelerometer.
Figures 6-7 through 6-9 show acceleration amplitudes at 50%, 75%,
and 100% load. Note the varying acceleration levels. Figures 6-7 and 6-8

FIGURE 6-7. 50% of load. Acceleration level = 6.2 g. (Source: Bently-Nevada
Corporation, Minden, Nevada).

indicate that at the end of the stroke of each piston, a hit occurred with an
additional intermittent hit within the single cycle. At these loads, this
intermittent hit was not consistent from cycle to cycle. At 100% load
(Figure 6-9) when the acceleration increased to its maximum level of
approximately 7.8 g's, the hitting became very dominant, along with the
intermittent hitting that occurred halfway through the cycle. All of these
patterns are characteristic of a problem in the compressor, probably
between the piston and the crankshaft. The compressor was shut down,
so an internal inspection could be done to determine the source of the
suspected problem.