Page 344 - Reciprocating Compressors Operation Maintenance

Troubleshooting Compressor Problems 329

on the length, size, and wall thickness of the suction pipe in relation to
the rotational speed of the compressor crankshaft.
The air noise can be substantially reduced by one or several remedial
measures:

1. Run the intake outdoors
2. Install a filter silencer
3. Use heavier piping on the suction line
4. Add or remove a short length of pipe on the suction line to avoid sym-
pathetic vibration in tune with pulsation frequency of the compressor
5. Interrupt the suction line with a section of leather, canvas, or
resilient material.
After becoming accustomed to the characteristic air noise of an air
compressor, any unusual knock can be assumed to have its source in the
mechanical running gear.

VALVE ANALYSIS

If a suction valve does not close and seal completely, the following occurs:

• During the compression stroke, some of the normally displaced gas
will leak or blow by to the inlet side of the valve. The design volume
of actual displaced gas will decrease. As the compressed hot gas
passes over the valve in the wrong direction, the valve heats up. The
inlet temperature of the gas on the suction side of the valve goes up,
thus reducing the volumetric efficiency of the machine, that is, hotter
than normal design suction temperature.
•The problem becomes compounded, the leakage gets progressively
worse, the moving parts, that is, strips, plates may distort due to
warpage from high temperatures. If enough heat is generated, carbon
will build up on the valve and the problem will worsen.

Leakage may also be caused by eroded valve seat gasket surface or a
jammed air unloading device.

EVALUATING RECIPROCATING COMPRESSOR CONDITION USING
_____ ULTRASOUND AND VIBRATION PATTERNS

As any gas (air, oxygen, nitrogen, etc.) passes through a leak orifice, it
generates a turbulent flow with detectable high frequency components.