Pressurized sealing groove for deactivating roller-follower

A valve deactivation assembly (21) comprises part of the valve gear train for an internal combustion engine, and is disposed in a bore (55) defined by the A engine block (11B). The assembly (21) includes a latching mechanism (67) shiftable, in response to control fluid pressure, between latched and unlatched conditions. The assembly (21) includes an outer body member (53), having an outer cylindrical surface (53S), reciprocable within said the bore (55), the outer body member including a lower terminal portion (55L). The outer body member defines an annular sealing groove (75) which remains aligned within the bore (55), between the lower terminal portion (55L) and a passage (72) communicating control fluid pressure the latching mechanism (67), as the outer body member reciprocates. There is also a fluid passage (77) disposed to communicate a source (79) of low pressure to the annular groove (75), to thereby form a barrier to block the migration of air to the control pressure passage (72).