US Patent 7104180 Low noise linear actuator

A linear actuator system including a cylinder, a piston slidably received within the cylinder and defining a piston chamber and a rod chamber in the cylinder, wherein the piston includes a plurality of orifices therethrough that place the piston chamber and the rod chamber in fluid communication, and a sealing member movable between a closed position, wherein the sealing member restricts fluid flow through at least one of the plurality of orifices, and an open position, wherein the sealing member is less restrictive of fluid flow through the orifices. The plurality of orifices may include an always-open orifice that is not blocked by the sealing member when the sealing member is in the closed position.