FLUIDDRIVEN REGLERAPPARAT

A fluid-operated apparatus receiving an input pressure signal exhibits a hysteresis or deadband effect by responding to an increasing pressure signal at a first level and a decreasing signal at a second and lower level. The apparatus includes a spool valve to which the input pressure signal is applied at one end of the spool. The opposite end of the spool having a given cross sectional area projects into a pressure chamber and contacts the poppet of a poppet valve held closed by a regulated pressure in opposition to forces produced by the spool. The seat of the poppet valve surrounds an opening into the pressure chamber so that the regulated pressure is admitted into the pressure chamber when the spool pushes the poppet open. The effective area of the valve seat is greater than the cross sectional area of the spool end engaging the poppet so that the force or input pressure signal required to move the spool and open the poppet valve is greater than that which permits the spool to return and close the poppet valve. A hysteresis or deadband effect determined by the different cross sectional areas is manifested by the spool movements and a hydraulic mechanism controlled by those movements.