Rotary Stepping Actuator for Valve

A valve system comprising:

• (i) a valve body configured with an inlet and an outlet and having flow trim configured to be moved axially by an externally threaded valve stem between a closed position, wherein flow through the valve body is restricted, and an open position, wherein fluid may enter the valve body through the inlet, pass through the flow trim at reduced pressure, and continue through the outlet;
• (ii) a stem/bonnet assembly connected to the valve body and including a bonnet disengagably connected with, and closing, an upper end of the valve body, the threaded valve stem extending through the bonnet, and a stem nut coaxial with the threaded valve stem and having internal threads cooperatively engaged with the externally threaded valve stem;
• (iii) an actuator housing coupled to the stem/bonnet assembly and forming an entry port for sealed entry and rotational mounting of the stem nut;
• (iv) an actuator drive shaft supported in the actuator housing for stepwise rotation in clockwise and counterclockwise directions, the drive shaft being co-axially aligned with, and configured to be rotatably coupled directly or indirectly to, the stem nut to impart rotation to the stem nut, the drive shaft forming at a periphery a first circular drive path and a second circular drive path co-axially spaced from the first drive path, each of the first and second drive paths comprising a number of outwardly-opening, circumferentially-spaced openings, the openings in the first and second drive paths being matched in number, size and spacing, and the openings in the first drive path being rotationally offset from the openings in the second drive path, based on midpoint to midpoint spacing of the openings, by a set fraction of the opening spacing;
• (v) a first actuation assembly mounted in the actuator housing adjacent the first drive path of the drive shaft and moveable from a retracted position through a forward actuation cycle, and operative to releasably engage one of the openings in the first drive path to incrementally rotate the drive shaft in a forward step through a predetermined angular increment set by the opening spacing in the counterclockwise direction when moved through the forward actuation cycle;
• (vi) a second actuation assembly mounted in the actuator housing adjacent the second drive path of the drive shaft and moveable from a retracted position through a reverse actuation cycle, and operative to releasably engage one of the openings in the second drive path to incrementally rotate the drive shaft in a reverse step through the predetermined angular increment in the clockwise direction when moved through the reverse actuation cycle;
• (vii) an actuation control system coupled with the actuator housing and configured to supply a discrete quantity of pressurized fluid to stepwise and separately drive the first and second actuation assemblies to impart stepwise counterclockwise and clockwise rotational movement to the drive shaft in the forward and reverse actuation cycles to move the flow trim in the forward and reverse steps between the open and closed positions;
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• (viii) the drive shaft and the first and second actuation assemblies being adapted to incrementally rotate the drive shaft in a counter step in a direction counter to the direction of a directly preceding step by an amount less than the predetermined angular increment, said amount being determined by the set fraction of the offset, such that the counter step in the counter direction rotates the drive shaft by said amount determined by the set fraction, while a next step in the same counter direction is a full step in the predetermined angular increment.