Let's start with some definitions.
In practical terms, hydraulic actuators are usually motors, or cylinders. Cylinders are also called linear actuators, since their motion is in a straight line. And hydraulic motors, of course, can also be referred to as rotary actuators.
Even though it's more to say, sometimes the term "rotary actuator" can be less confusing than "motor", especially when electric motors and heat engines start to enter the conversation.
The Rotary Actuators family is a little bigger than just hydraulic motors. It also includes semi-rotary actuators, like helical, rack and pinion, and vane actuators.
Helical
Rack and Pinion
Vane
Let's look at a simple hydraulic system that uses hydraulic motors.
For the sake of this example, only the right side driving circuit is shown.
This Generic Brand™ skid steer loader relies on a diesel engine to turn the hydraulic pump. The pump pushes hydraulic fluid through the propulsion and steering system, into the hydraulic motor.
Diesel engine converts chemical energy to rotational energy
Pump converts rotational energy to a combination of kinetic and potential energy
Motor converts the kinetic/potential energy combination back to rotational energy
Energy starts out at a prime mover (engine, or electric motor) and is converted multiple times, only to end at the shaft of a hydraulic motor. Many hydraulic systems begin with rotational energy, and after several energy-losing conversions, arrive back at rotational energy once more. Why bother with the whole hydraulic system and going to a rotary actuator, anyway? Isn't that inefficient?
The conversion to the hydraulic motors is very necessary. If the wheels were driven directly by the engine, the operator would be deeply unhappy with the skid steer loader’s performance! Both sets of wheels could only go in the same direction, and reverse would not be an option.
The skidsteer loader can drive, stop, and reverse thanks to the hydraulic motor.
The schematic symbol for a motor is a circle, with an arrow (or arrows) indicating the direction of flow. The arrow(s) will always point inward, representing flow into the motor.
Motor
Pump
Just like other schematic symbols, extra symbols can be "stacked" onto the basic motor symbol to indicate extra functionality.
Bi-directional Motor
Bi-directional Variable Displacement Motor
Bi-directional Variable Displacement Motor With Case Drain
Become a member to get immediate access to the rest of this lesson, and all the other great content on LunchBox Sessions.