A rotary actuator, comprising: a manifold block; and a first rotor assembly mounted to the manifold block; wherein the first rotor assembly includes: a first rotor shaft extending into the manifold block; a plurality of arcuate pistons attached to the rotor shaft, each arcuate piston curving at a set radial distance from a rotation axis of the first rotor shaft, and each piston attached to the first rotor shaft via a crank arm; a first pressure chamber assembly coupled to the manifold block, the first pressure chamber defining a plurality of piston pressure chambers each configured to receive and at least partially enclose a corresponding arcuate piston; a plurality of gland seals disposed adjacent an entrance to each piston pressure chamber and creating a seal between an inner surface of the piston pressure chamber and an outer surface of the corresponding arcuate piston inserted therein; wherein each gland seal includes an inner seal configured to engage a surface of the arcuate piston, and a plurality of outer seals configured to engage the inner surface of the piston pressure chamber, such that a hydraulic seal is formed between each piston pressure chamber and the corresponding arcuate piston inserted therein; the first rotor assembly being configured so that delivering a hydraulic fluid to the plurality of piston pressure chambers causes the arcuate piston disposed within each piston pressure chamber to translate at the set radial distance around the rotation axis of the first rotor shaft, thereby rotating the first rotor shaft. a manifold block; and a first rotor assembly mounted to the manifold block; wherein the first rotor assembly includes: a first rotor shaft extending into the manifold block; a plurality of arcuate pistons attached to the rotor shaft, each arcuate piston curving at a set radial distance from a rotation axis of the first rotor shaft, and each piston attached to the first rotor shaft via a crank arm; a first pressure chamber assembly coupled to the manifold block, the first pressure chamber defining a plurality of piston pressure chambers each configured to receive and at least partially enclose a corresponding arcuate piston; a plurality of gland seals disposed adjacent an entrance to each piston pressure chamber and creating a seal between an inner surface of the piston pressure chamber and an outer surface of the corresponding arcuate piston inserted therein; wherein each gland seal includes an inner seal configured to engage a surface of the arcuate piston, and a plurality of outer seals configured to engage the inner surface of the piston pressure chamber, such that a hydraulic seal is formed between each piston pressure chamber and the corresponding arcuate piston inserted therein; the first rotor assembly being configured so that delivering a hydraulic fluid to the plurality of piston pressure chambers causes the arcuate piston disposed within each piston pressure chamber to translate at the set radial distance around the rotation axis of the first rotor shaft, thereby rotating the first rotor shaft. a first rotor shaft extending into the manifold block; a plurality of arcuate pistons attached to the rotor shaft, each arcuate piston curving at a set radial distance from a rotation axis of the first rotor shaft, and each piston attached to the first rotor shaft via a crank arm; a first pressure chamber assembly coupled to the manifold block, the first pressure chamber defining a plurality of piston pressure chambers each configured to receive and at least partially enclose a corresponding arcuate piston; a plurality of gland seals disposed adjacent an entrance to each piston pressure chamber and creating a seal between an inner surface of the piston pressure chamber and an outer surface of the corresponding arcuate piston inserted therein; wherein each gland seal includes an inner seal configured to engage a surface of the arcuate piston, and a plurality of outer seals configured to engage the inner surface of the piston pressure chamber, such that a hydraulic seal is formed between each piston pressure chamber and the corresponding arcuate piston inserted therein; the first rotor assembly being configured so that delivering a hydraulic fluid to the plurality of piston pressure chambers causes the arcuate piston disposed within each piston pressure chamber to translate at the set radial distance around the rotation axis of the first rotor shaft, thereby rotating the first rotor shaft.