US Patent 10203046 Degressive pneumatic actuator spring rate

A valve actuator (100) and method for controlling such is disclosed. The valve actuator (100) may include a body (126), a piston (134), a first spring (136) displaceable between a primary position (154) and a secondary position (156), and a second spring (138) displaceable between a first position (158a) and a second position (160a). The first and second springs (136, 138) are configured to be simultaneously displaced during movement of the piston (134) from a first piston position (142) to a second piston position (144). The first spring (136) is configured to compress to a higher first spring force (F1) during displacement from the primary position (154) to the secondary position (156), and the second spring (138) is configured to have a decreasing second spring force (F2) during displacement from the first position (158a, 158b) to the second position (160a, 160b), the second spring force (F2) decreasing non-linearly.