Single annular membrane type of pneumatic positioner

A pneumatic positioner for use with a fluid motor having a piston rod, said pneumatic positioner comprising:

• a generally hollow body defining an annular control pressure air chamber in said body;
• an annular diaphragm forming one wall of said air chamber, said annular diaphragm having in its center an opening and being rigidly mounted to said body at both its inner and outer peripheries,
• a dish-like member engaging a circular area of said diaphragm between its inner and outer peripheries;
• biasing means for applying a variable biasing force to said dish-like member in the direction of said diaphragm and in response to the position of the piston rod;
• a valve stem engaging at its one end said dish-like member and extending through a hole in said body concentric with the center of said diaphragm and said air chamber,
• said valve stem being slidably movable within said hole without contact with said body;
• a valve operably coupled to said valve stem for controlling the flow of fluid to and from said motor.