Chapter 9 Hydraulic Actuator PREPARED BY MOHD SHAHRIL

Chapter 9 Hydraulic Actuator PREPARED BY MOHD SHAHRIL SHARIFF

Hydraulic Drive Section ØThe drive section/actuator of a hydraulic system is the part of the system which executes the various working movement of a machine or manufacturing system. ØThe energy contained in the hydraulic fluid is used for the execution of movements or the generation of forces (e. g. clamping processes) ØThus, hydraulic actuators are devices used to convert pressure energy of the fluid into mechanical energy ØThis is achieved using the following components: 1. Linear actuator: For linear actuation (hydraulic cylinders). 2. Rotary actuator: For rotary actuation (hydraulic motor). 3. Semi-rotary actuator: For limited angle of actuation (semi-rotary actuator).

Hydraulic Drive Section (cont. )

Hydraulic Cylinders §A hydraulic cylinder is a device, which converts fluid power into linear mechanical force and motion. §It usually consists of a movable element, a piston and a piston rod operating within a cylindrical bore.

PARTS OF A HYDRAULIC CYLINDER A hydraulic cylinder consists of the following parts • Cylinder barrel • Piston rod • Bush • Cylinder head and cap

TYPE OF HYDRAULIC CYLINDER Types of Hydraulic Cylinders Hydraulic cylinders are of the following types: �Single-acting cylinders. �Double-acting cylinders. �Telescopic cylinders. �Tandem cylinders.

Single Acting Cylinder • It consist of piston inside a cylindrical housing called as Barrel • On one end is attached a rod, which can reciprocate • At the opposite end, there is a port for the entrance and exit of the oil • They produce force only in one direction by hydraulic pressure acting on the piston • The return of the spring is not done hydraulically, it is either done by gravity or spring.

Single Acting Cylinder (cont. )

Double Acting Cylinder Two types of double-acting cylinders: Ø Double-acting cylinder with a piston rod on one side. ØDouble-acting cylinder with a piston rod on both sides.

Double-Acting Cylinder with a Piston Rod on One Side Figure shows the operation of a doubleacting cylinder with a piston rod on one side. To extend the cylinder, the pump flow is sent to the blank-end port as in Fig. The fluid from the rod-end port returns to the reservoir. To retract the cylinder, the pump flow is sent to the rodend port and the fluid from the blank-end port returns to the tank as in Fig.

Double-Acting Cylinder with a Piston Rod on Both Sides A double-acting cylinder with a piston rod on both sides (Fig. )is a cylinder with a rod extending from both ends. This cylinder can be used in an application where work can be done by both ends of the cylinder, thereby making the cylinder more productive. Double-rod cylinders can withstand higher side loads because they have an extra bearing, one on each rod, to withstand the loading.

Telescopic Cylinder §A telescopic cylinder is used when a long stroke length and a short retracted length are required. §The telescopic cylinder extends in stages, each stage consisting of a sleeve that fits inside the previous stage. §Most telescopic cylinders are single acting (push). §Double acting telescopic cylinders must be specially designed and manufactured. §They are more expensive than standard cylinders due to their more complex construction.

Telescopic Cylinder. . (cont. ) §When the cylinder extends, all the sections move together until the outer section is prevented from further extension by its stop ring. §The remaining sections continue out-stroking until the second outermost section reaches the limit of its stroke; this process continues until all sections are extended, the innermost one being the last of all.

Telescopic Cylinder. . (cont. ) One application for this type of cylinder is raising a dump truck bed.

Tandem Cylinder A tandem cylinder, shown in Fig, is used in applications where a large amount of force is required from a smalldiameter cylinder. Pressure is applied to both pistons, resulting in increased force because of the larger area. The drawback is that these cylinders must be longer than a standard cylinder to achieve an equal speed because flow must go to both pistons.

Graphical Symbol

Hydraulic Motors • A hydraulic motor transform hydraulic energy into mechanical energy which is applied to a resistance object by means of a shaft connected with the motor. • In hydraulic motor the rotating elements(i. e. vanes, gear, piston, etc. ) are pushed by the oil pressure to enable the motor shaft to rotate & thus develop the necessary turning torque & continuous rotational motion.

Hydraulic Motors (cont. ) Hydraulic motor (gear motor with two direction rotation)

Semi/Limited Rotary Motors §The limited angle rotary actuator is applied when the shaft has to rotate over a limited angle. §The figure shows how this simple actuator works: in this case the shaft can rotate over an angle of about 270 degrees. §This type of actuator is, among others, used as a rotator actuator on (small) cranes and excavators