Nitrogen die cylinder

Claim 1

In combination a manifold having a pressurized nitrogen chamber for applying a biasing force to a die member that is vertically displaceable in response to vertical reciprocation of the plate of a press in which the die member is mounted, a cylinder mounted on said manifold, said cylinder having a bore, the lower end of which communicates with the pressurized chamber of the manifold, a piston slideably mounted in said bore and biased upwardly therein by the manifold pressure at the lower end thereof, the lower end portion of the piston having a lower, bottom high pressure annular seal thereon engaging said bore, the portion of the piston above said bottom seal being of a reduced smaller diameter than said bore so as to define therebetween an annular chamber having a cross sectional area substantially smaller than the cross sectional area of the piston, said cylinder having an opening at its upper end through which the reduced diameter portion of the piston projects, an upper annular high pressure seal in said opening engaging the outer periphery of the reduced diameter portion of the piston, said piston having a central chamber therein communicating with said annular chamber, said lower seal preventing communication of said annular and central chambers with said manifold chamber and said upper seal preventing communication of said annular and central chambers with the atmosphere surrounding the cylinder, said seals being of the type whose sealing characteristics are enchanced when subjected to relatively high axial pressures in an upwardly direction and means for constantly applying an axial upward pressure to said upper seal at a value below the pressure in the manifold chamber.