Pressure and temperature compensating hydraulic valve

Abstract

When a Hydraulically operated valve is used to control the operation of a hydraulic elevator, it is required to do so in a manner such that as the elevator cab approaches a floor level in either direction, it is first decelerated through a transition cycle and after that moved slowly a short distance through a creeping cycle to the floor level where it stops. In the up direction, an extra heavy load cuts the transistion time and adds objectionably to the time needed for up leveling. The compensating valve of the invention is interposed in the hydraulic line of the operating valve which normally is depended on to cause deceleration for transition, replacing the deceleration valve. A plunger in the compensating valve is shifted by an increase in hydraulic pressure resulting from an extra heavy load. The shifting causes some of the series of bleed ports to close slowing down return hydraulic flow through the compensation valve which results in readjusting the transition time to what it would be for a light load or no load condition in the cab. Bi-metallic thermally responsive discs acting between the plunger and the housing further modify plunger movement to compensate for change of temperature in the hydraulic fluid such that for example, for a less viscous fluid due to higher temperature the plunger is permitted to move further under pressure of the hydrualic fluid thereby also to close some of the bleed ports and further readjust the transition cycle.