What are Rotary Actuators?

Hydraulic rotary actuators are compact units which generate very high torque in small spaces using hydraulic pressure. Since they can be controlled precisely and easily despite their high power, HKS rotary actuators have been a success in almost every area where limited rotary movements with high torque are required.

High manufacturing precision is required in order to achieve this functional efficiency and reliability. The actuator’s interior is perfectly protected and completely immune to dust, dirt and moisture. This precision, along with the strong, well-sealed housing, allows the actuator to withstand operating pressures up to 350 bars. Rotary actuators can also be used under very harsh conditions, underground as well as 2300 meters below sea level. As an example, 224 actuators were used during the recovery of the Russian atomic submarine „Kursk“ to ensure that it was held horizontally, thereby enabling the salvage efforts to be carried out safely. Actuators are even used in the pharmaceutical and food processing industries where a high degree of cleanliness and hygiene are required.

Based on the actuator‘s small physical presence, its strength and reliability may not be perceivable. The strongest HKS rotary actuator model can turn over twenty VW Golf automobiles from side to side.


Three categories may be distinguished:

Rack and pinion principle


The oil pressure exerted by both connections causes a rotational movement in the primary shaft. In doing so, the linear movement of the piston is transformed into rotational movement due to multiple contradirectional quick-acting screw threads on the housing, piston and shaft.