Scavenge valve for a two-cycle engine

A valve for use in controlling the amount of working fluid purged from a cylinder of an engine prior to combustion, comprising:

• a piston received in and forming part of a chamber in a housing;
• said housing including an aperture formed about said chamber and an inlet upstream of said aperture;
• said piston movable between first and second positions to open and close communication between said aperture and said inlet, said inlet adapted to receive pressurized fluid;
• first means for selectively establishing and terminating communication of said chamber with an outlet whereby when communication is established a pressure force differential is created across said piston to urge same downstream, toward said first position, to uncover said aperture to permit flow from said inlet through said aperture;
• means for balancing the pressure forces acting on upstream and downstream surfaces of said piston, such balancing means effective during intervals when said first means terminates communication of said chamber to said outlet;
• and
• means for urging said piston in an upstream direction toward said second position to prohibit flow from said inlet through said aperture, wherein said piston further comprises a first member, including an opening defining on an upstream portion thereof a first surface and an axially extending walled member surrounding said first member including an upstream end defining a second surface and a downstream end defining a third pressure receiving surface, and wherein said first member is recessed from said downstream end and wherein when said piston is in said second position said second surface is in contact with a portion of said housing such that the applied pressure does not operate thereon and when said piston is moved in a downstream direction said applied pressure acts upon said first and second surfaces wherein said piston further comprises a pressure receiving fourth surface, opposite to and downstream of said first surface and located on a downstream side of said first member;
• wherein the downstream portion of said walled member is slidably received upon a hollow extending portion of said housing, and wherein said extending portion includes means for communicating fluid from said opening to said third surface.