In service, the internal components of a reciprocating compressor valve, comprising springs, and a stiff perforated membrane are subjected to repeated cyclic loading at a frequency of approximately 20 Hz (equivalent to a synchronous motor speed of 1300 rpm). The failure mechanism of the device is typically associated with either failure of the return spring, used to preload the membrane, or failure of the membrane itself due to fatigue cracking between perforations
An ElectroPuls™ E3000 test instrument was used to investigate the fatigue life and failure mechanisms of these compressor devices at frequencies above 20 Hz. This particular compressor manufacturer supplied the internal components of the valve and fixtures were manufactured to fit them into the test instrument. SAX single-axis fatigue software was used to define and run the tests.
Three different test scenarios were successfully run:
- A digital position controlled test to model basic loading of the springs
- A position controlled test using the Advanced Amplitude controls in SAX to provide outer-loop control with a 2 mm positive position peak and -38 N compression lower peak. This test simulates full stress loading of the springs prior to valve having full contact.
- A digital position controlled test with amplitude and mean position to produce impact loads in the region of -150 N at 20 Hz, simulating the valve in full contact.