Redundant high-pressure seal for fluid spring

Claim 1

In a pneumatic spring including a cylinder having a side wall, a closed end wall and an apertured end wall defining a sealed cavity therein, a piston rod axially movable into and out of the cavity through the apertured end wall, a piston carried by the piston rod for axial movement within the cavity, a pressurized fluid within the cavity, and fixed sealing means adjacent the apertured end wall and enveloping the piston rod for establishing a seal between the piston rod and the cylinder against substantially the full pressure, relative to atmospheric, of said pressurized fluid, the improvement comprising: floating sealing means, disposed between the fixed sealing means and the piston and enveloping the piston rod, for establishing a seal between the piston rod and the cylinder capable of sealing against substantially the full pressure, relative to atmospheric, of said pressurized fluid, said floating sealing means being axially movable relative to said piston rod and said cylinder and defining with said fixed sealing means a sealed chamber of variable volume surrounding said piston rod; a liquid filling said sealed chamber, the pressure exerted on said floating sealing means by said pressurized fluid being transmitted to said liquid so that the pressure differential across said floating sealing means is relatively small so long as said sealed chamber remains filled with said liquid; and in the event of leakage of said liquid past said fixed sealing means, said floating sealing means being axially movable outwardly towards said fixed sealing means to contain said liquid in surrounding relationship to said piston rod and, in the event of complete loss of liquid past said fixed sealing means, said floating sealing means functioning as a back-up seal against the loss of said pressurized fluid from said cavity.