Detailed hydraulic actuator in hydraulic system, how to choose hydraulic actuator!

Modern hydraulic systems are very similar to human bodies. The heart works by pumping blood into all parts of the body. The brain is the central unit that controls the eyes and ears (sensors), as well as the muscles of the human body as an output device for performing various tasks. These output devices in hydraulic systems are called actuators.

What is a hydraulic actuator?

Hydraulic actuators are fully mechanical components, and do not need to transfer the required power and speed. In order to execute the required operation group, the feedback loop of servo control is used to command control valves (pressure control valves, flow control valves and direction control valves) to control the amount of hydraulic energy entering the actuator. Hydraulic actuators blindly convert hydraulic energy into mechanical energy (a function of force and speed or torque and speed), without considering it.

Hydraulic actuators can be divided into two categories: linear and rotary, and provide different types of forces.

Different types of forces

Linear hydraulic actuator

Linear hydraulic actuators provide forces in a linear manner, while rotary actuators provide torque and rotation speed. The main difference between linear and rotary actuators is that linear actuators provide different forward and backward speeds (due to the area occupied by the piston rod), while rotary actuators always provide the same rotation speed in any direction.



Rotary actuators require sliding seals, which can lead to more leakage problems than piston and cylinder types. To prevent this, for most rotary applications, linear motion is generated by linear actuators and converted to rotary motion by racks and pinions. Therefore, linear hydraulic actuators provide maximum force-weight ratio and are mainly used for mobile applications (cranes, loading and unloading trucks, special mining rigs, etc.). They are also used for applications requiring very high force/pressure, such as punches, because linear actuators can be single-acting or dual-acting.

The single-acting cylinder is actuated by hydraulic force during forward motion and returns to its initial position by spring. There are two ports at both ends of the dual-acting cylinder, and the fluid can enter from both sides according to the DCV. Therefore, the dual-acting cylinder can provide force in two directions, which is a very useful choice.



Choosing the right hydraulic actuator

The choice of hydraulic actuators depends on the application required. The maximum force produced by using the hydraulic cylinder depends on the maximum pressure produced by the pump and the area of the actuator. Because the maximum pressure produced by the pump is limited by the safe working pressure, the system (pipes and valves) can be handled faultlessly, so the area of the cylinder plays a major role in the selection process.



To determine the size of the actuator suitable for any application, you need:

Find strength requirements. If it is used for lifting purposes, the force must match the weight of the device. If the application requires moving the load on the ground, the hydraulic pressure will only need to cover the friction (which will be smaller).

Find out where the force is. If the force is eccentric, consider a larger diameter piston rod to avoid bending.

Calculate the bore size of the cylinder according to the maximum force requirement and the maximum pressure generated by the system. Since the piston rod is only on one side, the area will be different because one side is fully open to the fluid and the other side is connected to the piston rod. Therefore, the available area will be reduced. According to experience, the diameter of piston rod should be half of the inner diameter of hydraulic cylinder, so the available area of piston rod side is 75% of the open side area. Because the stroke length is constant, the volume is proportional to the area. Therefore, for the same flow rate provided by the pump, the differential momentum will change the speed. In order to maintain the same speed in any direction, a two-rod cylinder is used, which has a cylinder rod on either side of the piston. The force produced by the single-rod double-acting cylinder is also different, because the force is proportional to the area.

Speed = cylinder volume/flow

Force = pressure*area

Buffer factor

In order to avoid the impact of piston on the cylinder head and improve the service life of the hydraulic cylinder seals, a rapid deceleration is needed at the end of the stroke. The ideal buffer is when the piston reaches zero speed because it reaches the end of the cylinder without impact. When the piston reaches the end, some fluid is intercepted and passed through the throttle valve, which provides additional resistance and thus decelerates. Screws can be used to adjust the profile of the throttle valve to control deceleration.