Page 347 - Reciprocating Compressors Operation Maintenance

332 Reciprocating Compressors: Operation and Maintenance

The Beta 250 has three pressure channels, providing real time compu-
tation and display of cylinder HP and suction discharge HP losses.
Excessive suction or discharge valve loss is a clear indication of poor
valve condition.

VIBRATION vs CRANKANGLE PATTERNS

The use of vibration and ultrasonic patterns in combination with cylin-
der pV patterns will aid in diagnosing the condition of valves, rings, and
packing. When valves open and close, they produce vibrations that are
detected with an accelerometer. Figure 5-5 shows a compressor pressure
vs crankangle trace. The vibration and ultrasonic patterns are also shown.
These indicate valve timing and normal valve action.

Suction Valve Suction Valve Discharge Valve
Opening Closing Opening
Discharge
Valve
Closing
Vibration

Pressure

Ultrasonic

TDC BDC TDC
FIGURE S-5. Pressure-time trace (pressure angle) with vibration and ultrasonic
traces superimposed.

The accelerometer is attached to the valve cover with a magnetic
clamp and is moved from cover to cover to detect faults. If the spring
tension in the valves is too light, a late closure of the valve will result. If
the spring is too heavy, multiple premature closures of the valve are like-
ly to occur. These can be detected with the vibration trace on the C.R.T.
screen as illustrated in Figure 5-6.