Gauge cylinder assembly for position indicator and indicator system including such cylinder

Claim 1

A volumetric gauge cylinder for a position indicator comprising a closed cylinder having connections for pressure fluid at its ends, a non-rotatable piston movable within said cylinder under the fluid pressure, a rotatable spindle extending along the length of said cylinder having a helical external configuration cooperating with, and forming a sealed fit with a correspondingly shaped opening in said piston so that linear movement of said piston is translated into rotary movement of said spindle, an external indicator rotating in accordance with the movement of said spindle, said piston including a pair of oppositely connected, spring-loaded pressure relief valves which remain closed during normal operation but open to permit the flow of pressure fluid if the pressure exceeds a predetermined value when said piston reaches either end of its stroke, a hollow guide rod for said piston having a sealing fit with an opening in said piston extending between the two ends of said cylinder at one of which its interior communicates with an external connection for pressure fluid and at the other of which its interior communicates with the interior of said cylinder to form the pressure fluid connection at that end.