Combination diaphragm piston actuator

An apparatus for actuating a valve, the apparatus comprising:

• an actuator housing having a valve end, a cap end, a central axis, and a sidewall defining an inner diameter of the actuator housing;
• a cap connected to the cap end of the actuator housing;
• a plate positioned within the actuator housing, the plate having a center portion and an outer diameter that slidingly engages the inner diameter of the actuator housing;
• a pressure chamber located within the actuator housing between the plate and the cap, the plate moving between a plate-up position and a plate-down position in response to pressure media injected into the pressure chamber, the plate being nearer the valve end in the plate-down position than in the plate-up position;
• a seal nut connected to the plate, the seal nut operable to engage a central opening of a diaphragm;
• and
• a cap seal fluidly sealing the pressure chamber between the cap and the actuator housing;
• wherein
• the pressure chamber is fluidly sealed at the plate by one of a first plate seal assembly and a second plate seal assembly;
• and wherein
• the first plate seal assembly is formed by the diaphragm being secured between the seal nut and the plate;
• the second plate seal assembly is formed by an outer diameter sidewall seal located between the inner diameter of the actuator housing and the outer diameter of the plate and a retainer seal located between an outer diameter of the seal nut and an inner diameter of the plate;
• and
• wherein
• the diaphragm moves between a shortened position when the plate is in a plate-up position and the diaphragm has a bellows shape in cross section the bellows shape having at least one inner loop with an inner loop inner diameter and at least one outer loop having an outer loop outer diameter, and an extended position when the plate is in a plate-down position, by expanding the bellows shape axially and reducing a radial distance between the inner loop inner diameter and the outer loop outer diameter, measured relative to the central axis such that one or more of the at least one inner loops contacts the sidewall of the actuator housing, and wherein the at least one outer loop and the at least one inner loop are spaced axially apart.