Abstract: A mechanism is provided for maintaining an open door in a selected fixed position includes a keyed shaft which passes through a plurality of elliptically shaped discs via apertures centrally located in the discs are mounted. The long axis of each disc is aligned to that of the other discs and the discs are pressed together from either side along the axis of the shaft between two compression springs. Angled stop members located to the outside of the compression springs displace the discs along their long axis at a small angle from the plane perpendicular to the shaft. The small angle is chosen to produce a substantially circular projection of the discs in a plane perpendicular to the shaft. The shaft, with its mounted discs, springs, and angled stop members, is placed within a housing of cylindrical cross section having an interior diameter selected such that the discs are in frictional contact with the internal surface of the housing and the shaft is thus slidably but frictionally disposed in the housing.

Abstract: A mechanism is provided for maintaining an open door in a selected fixed position includes a hydraulic cylinder having first and second ends. One end of a shaft axially disposed in the cylinder, passes through a hydraulic seal at one end of the cylinder. A piston is axially disposed on the shaft near its other end, and includes o-rings for sealing it against the cylinder walls. The piston includes first and second axially-disposed bores. First and second discs, each including an aperture are axially mounted on the shaft in contact with the opposing faces of the piston and are positioned such that the aperture of each is substantially aligned with one of the bores and blocks the other bore. The discs are held against the faces of the piston with a predetermined amount of force.