Normally unseated suction valve

摘要

In its unstressed state, a suction valve (20) is spaced from its valve seat (30-1) such that the suction valve (30) must be deformed against its inherent spring force in order to achieve seating. The spring force due to deformation provides an opening bias to the suction valve (30) such that it opens earlier in the suction stroke and offsets the effects of adhesion due to the presence of oil between the seating surface (30-la) and the valve (20).