Description

Hydraulic rotary actuators use a pressurized, incompressible fluid to rotate mechanical components. They are faster and more powerful than pneumatic actuators because the high pressures used in hydraulic systems produce greater torque.

Rotational Elements

Hydraulic rotary actuators use two types of rotational elements: circular shafts and tables. Typically, circular shafts include a keyway while tables include a bolt pattern for mounting other components.

Shaft Type

• Single-shaft devices provide an output on only one side of the actuator.

• Double-shaft devices provide outputs on both sides of the actuator.

Operation

To convert linear motion into shaft rotation, helical spline teeth on the shaft engage matching splines on the inside diameter of a piston. As hydraulic pressure is applied, the piston is displaced axially within the housing and the splines cause the shaft to rotate. When a control valve is closed, hydraulic fluid is trapped inside the housing and the shaft is locked in place.

Actuator Type

• Single-piston devices drive a rack that rotates the pinion.
• Double-piston and four-piston devices drive racks on both sides of the pinion.
• Single-chamber and double-chamber rotary vanes that are actuated by pressurized fluid are also available. 

Performance Specifications

Performance specifications for hydraulic rotary actuators include operating pressure range, maximum torque, load capacity, linear stroke, operating temperature, and rotation angle.

• Maximum torque is the required range of torque output.
• There are two types of load capacity: axial load capacity and radial load capacity.
  • Axial load capacity is the required axial or thrust load capacity of the output shaft or table.
  • Radial load capacity is the required radial load capacity of the output shaft or table.
• Linear stroke, another important specification, is the travel distance between the fully retracted and fully extended rod positions.
• Operating temperature is a full-required range.

• Rotation angle is the degree to which the actuator can rotate before reaching its travel limit. Typically, hydraulic rotary actuators provide a maximum rotation angle of 45°, 90°, 135°, 180°, 225°, 270°, 315°, or 360°. 

  • Angles can be adjusted via screws on one side, or on both ends of the angular stroke. Actuators such as true rotary indexers allow multiple position stops along strokes. 

Applications

Hydraulic rotary actuators are used in a variety of marine, mining, military, construction, and recycling applications. For example, some devices are used to provide propeller steering for outboard hydraulic propulsion systems used on marine vessels such as barges. Other devices are used in bulldozers, excavators, and other earth moving equipment for performing extensive grading and sloping with different angles. Hydraulic rotary actuators are also used in self-propelled aerial work platforms and in many vehicle steering systems.

Standards

BS EN 15714-4 - This document provides basic requirements for hydraulic part-turn valve actuators, both double acting and single acting, used for on-off and modulating control duties.

MIL-A-24533 - This specification covers the requirements for material, design, fabrication, and testing of rack-and-pinion hydraulic rotary actuators for Naval shipboard use.

Resources

BOOK 2, CHAPTER 19: Rotary Actuators

How Hydraulic Rotary Vane Actuators Work

Image Credits:

Rotork plc | Turn-Act, Inc.