Opportunities for failure are many. Seal integrity around the piston cylinder wall reduces the efﬁciency of compression. Dirty and worn valves do not seal properly due to corrosion and build up around the valve head. Internal leakage around the piston and the valve head can be detected with ultrasound inspection by recording a dynamic ultrasound signal thanks to a TRAPChecker or an SDT340 and analyzing it in the time domain. Early mechanical failures which can eventually lead to screwdriver detectable valve knocking can be seen this way too.
In ﬁgure 3, we can clearly see the impact made by the valve when it is seated and the suction of turbulent air ﬂow when the valve is opened. High amplitude signals between the valve impacts can reveal mechanical looseness (early knocking) or internal leakage from piston rings or valve seat. Comparison between similar valves is done easily by scaling the Y-Axis of the time signal and presenting in overlay or side-by-side mode.
A documented report that can cite the historical evolution of your compressor’s health is an extremely valuable and professional way to present your data. It is a great way to convey to maintenance managers that a problem is escalating and that action is required. It will hold much more credibility than walking into your bosses’ ofﬁce, grease dripping from your ear lobe, and suggesting that a compressor valve sounds like a “bongo drum” and it should be immediately removed from service.