Pneumatic hammer in an externally pressurized orifice-compensated air journal bearing

An experimental study was made of the occurrence of pneumatic hammer in an externally pressurized air journal bearing having double plane admission. Various parameters affecting the onset of pneumatic hammer were investigated. These were:- supply recess depth, supply orifice diameter and bearing mass. In general, pneumatic hammer is relatively easily avoided in journal bearings. However, achievement of repeatable results proved difficult, because of the effects of external damping and support stiffness. These factors are not incorporated in the existing theory. There were a significant number of instances where pneumatic instability was not apparent, although existing theory gave a strong indication of its occurrence. When pneumatic hammer did occur, there was broad agreement between experimental results and predicted trends as regards supply recess volume and supply orifice diameter, but not as regards bearing mass. The effects of external damping were important.