while hydraulic hammers use hydraulic pressure for percussion and air mostly for flushing, pneumatic hammers use air pressure for both percussion and flushing. Most pneumatic drills have inbuilt compressors but pneumatic machines have compressors as separate machines. For both machines the shank adaptors are most worrisome. This is because people buy machines without consideration for availability of the models backup. This being a perishable item becomes problematic if the model is not available in the locality. Another problem arises if one ends up with T51. This has low machine population and therefore scarce and expensive.