According to another embodiment of the invention, the pockets are defined by inturned edges on the covers which embrace a boundary of {HEAD ~ a recess} formed in {TAIL ~ the surface} of the movable element exposed to hot gases of combustion 
According to another embodiment of the invention , the pockets are defined by inturned edges on the covers which embrace a boundary of { HEAD ~ a recess } formed in { TAIL ~ the surface } of the movable element exposed to hot gases of combustion
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH