the cam lift with air residing in the piston space 18 being conducted into the upper annular space 20 via bores 19 23 the bore 23 in the housing 2 aiding the overflow forms a control edge 43 in the area most distant from the cam 52 see fig2 the bore 23 with its control edge 43 are thereby positioned in such a way that the piston 4 entraps a residual amount of air in the piston space 18 extending to the base 16 when it passes the control edge 43 on its axially downward motion since at this point air can no longer flow from space 18 into space 20 a further escape of the residual amount of air in the piston space 18 is effected through a channel 44 extending in the bore 10 of the piston 4 axially away from the cam 52 the channel 44 terminates with its cam distal end in a lower annular space 45 between the inner element 9 and the housing 2 for receiving the compression spring 5 the air pushed out of the piston space 18 can escape therefrom through discharge openings 46 distributed around the circumference of the housing 2 into not shown exhaust lines of the cylinder head 50 the cross section of channel 44 including the possibility of having several channels per.