Force Limited Valve Actuator and Method Therefor

Abstract

The force limited valve actuator operates on light-duty valves. The actuator includes signal controlled motor which drives a two piece threaded screw-nut drive. The nut connected to the motor and the screw connected to the valve stem. The nut has a spring loaded actuation surface/plate. The nut body has a positional indicator stem used as a valve-motor control. Operationally, the screw-nut-set moves between first, second and third positions. First: actuation plate at neutral and valve-stem at valve OPEN stop (example). Second: screw protrudes outboard of nut and valve-stem at CLOSE stop and actuation plate at neutral. Third: plate moves away from valve-stem (beyond neutral) while stem at CLOSE which third movement is a force sensor. First, second and third positions are all one way screw rotation. Force limited on stem by damper-shock absorber action. The positional indicator effects ON-OFF valve control.

1 . A method of limited force on a valve stem of a light duty valve actuated with less than 1,100 N operative between open and closed positions, said valve controlled by a valve control signal, comprising:
 providing a threaded drive with screw and nut elements disposed in an actuator housing;   providing a spring between said nut element and said actuator housing   linearly moving said valve stem in a first direction by screwed rotation of said nut element with respect to said screw element until reaching one or the other of said open and closed positions;   thereafter linearly moving said nut element in a second direction, opposite said first direction, against said spring;   sensing force on said valve stem during the linear movement of said nut element in said second direction;   thereby establishing one of a damper action and a shock absorber action between said valve stem and motor via said spring and thereby establishing during movement in said second direction via said spring, one of a damper action, a shock absorber action and a force limiter action between said valve stem and motor.   
     
     
         2 . A method of limited force on a valve stem of a light duty valve actuated with less than 1,100 N operative between open and closed positions, said valve controlled by a valve control signal, comprising:
 providing a threaded drive with screw and nut elements disposed in an actuator housing;   providing a spring between said screw element and said actuator housing   linearly moving said valve stem in a first direction by screwed rotation of said screw element with respect to said net element until reaching one or the other of said open and closed positions;   thereafter linearly moving said screw element in a second direction, opposite said first direction, against said spring;   sensing force on said valve stem during the linear movement of said screw element in said second direction;   thereby establishing one of a damper action and a shock absorber action between said valve stem and motor via said spring and thereby establishing during movement in said second direction via said spring, one of a damper action, a shock absorber action and a force limiter action between said valve stem and motor.