Unit 2. and Power Unit  Introduction:  An is a component of that is responsible for moving or controlling a mechanism or system.

 The supplied main energy source may be electric current, pressure, or pneumatic pressure. When the control signal is received, the actuator responds by converting the energy into mechanical motion.

 It is a device which converts into rotary power or converts fluid pressure into torque or linear power. Introduction- . They extract energy from a fluid, and convert it to mechanical energy to perform useful work. . Hydraulic cylinders, also called linear actuators provide a that drives an external load along a straight line. . Hydraulic motors, also called rotary actuators, provide a torque that drives an external load along a circular path.

Hydraulic F x v System V x I P x Q Electric T x ω Hydraulic Motor Pump T x ω Hydraulic Motor Difference between Hydraulic Motor and Hydraulic Motor Hydraulic Pump It is a device for delivering torque at a It is a device for delivering flow at a given pressure. The main emphasis is on given pressure. The main emphasis is on mechanical efficiency and torque that volumetric efficiency and flow. can be transmitted. Motors usually operate over a wide Pumps usually operate at high RPM. range of speed, from a low RPM to high RPM. Most motors are designed for In most situations, pumps usually bidirectional applications such as operate in one direction. braking loads, rotary tables. Motors may be idle for long time Pumps usually operate continuously.

Motors are subjected to high side loads Majority of pumps are not subjected to (from gears, chains, belt-driven pulleys). side loads. Comparison between a Hydraulic motor and an Electric motor Electric Motor Hydraulic Motor Electric motors cannot be stopped Hydraulic motors can be stalled for any instantly. length of time. Their direction of rotation cannot be Their direction of rotation can be reversed instantly. instantly reversed and their rotational This is because of air gap between the speed can be infinitely varied without rotor and stator and the weak magnetic affecting their torque. field. They can be braked instantly and have immense torque capacities. Electric motors are heavy and bulky. Hydraulic motors are very compact compared to electric motors. For the same power, they occupy about 25% of the space required by electric motors and weigh about 10% of electric motors.  Applications:

Applied directly to the work.

They provide excellent control for acceleration, operating speed, deceleration, smooth reversals and positioning.

They also provide flexibility in design and eliminate much of bulk and weight of mechanical and electrical power .

A hydrostatic transmission converts mechanical power into fluid power and then reconverts fluid power into shaft power.

The advantages of hydrostatic transmissions include power transmission to remote areas, infinitely variable speed control, self-overload protection, reverse rotation capability, dynamic braking and a high power-to-weight ratio.

Eg: Material-handling equipment, farm tractors, railway locomotives, buses and tools Rotary actuators- 1.Gear Motors: Working- A gear motor develops torque due to hydraulic pressure acting against the area of one tooth. There are two teeth trying to move the rotor in the proper direction, while one net tooth at the center mesh tries to move it in the opposite direction. In the design of a gear motor, one of the gears is keyed to an output shaft, while the other is simply an idler gear. Pressurized oil is sent to the inlet port of the motor. Pressure is then applied to the gear teeth, causing the gears and output shaft to rotate. The pressure builds until enough torque is generated to rotate the output shaft against the load. The side load on the motor bearing is quite high, because all the hydraulic pressure is on one side. This limits the bearing life of the motor. 2.Vane Motors: 3.Axial Piston Motors: Axial Piston Motors: 4.Swash-plate piston motor

5.Bent-Axis Piston Motors:

6.Radial Piston Motors: Performance of Hydraulic Motors: 1.Starting torque: The starting torque is the turning force the motor exerts from a dead stop.

2. Running torque: Running torque is exerted when the motor is running and changes whenever there is a change in fluid pressure.

3. Stalling torque: Stalling torque is the torque necessary to stop the motor. Volumetric efficiency:

Mechanical efficiency:

Here, Overall efficiency: Example: A hydraulic motor receives a flow rate of 72 LPM at a pressure of 12000 kPa. If the motor speed is 800 RPM, determine the actual torque delivered by the motor assuming the efficiency 100%? Cont.

Semi-Rotary Actuators- Devices used to convert fluid energy into a torque which turns through an angle limited by the design of the actuator 1.Vane-Type Semi-Rotary Actuator 1.1(Single Vane)- A semi-rotary actuator allows only a partial revolution. A vane-type semi-rotary actuator consists of a vane connected to an output shaft. When hydraulic pressure is applied to one side of the vane, it rotates. A stop prevents the vane from rotating continuously. The rotation angle in the case of a single-vane semi-rotary actuator is 315°. 1.2.Two-Vane-Type Semi-Rotary Actuator-

The advantage of this design is that the torque output is increased because the area subjected to pressure is large.

However, two-vane models cannot rotate as many degrees as can single- vane models.

It is limited to 100°. 2.Chain and Sprocket Semi-Rotary Actuator- It is suitable for multi-revolution applications. The larger cylinder is the power cylinder and the smaller cylinder is the chain return or seal cylinder . The larger piston moves away from the port due to differential areas of the two pistons. The movement of larger piston pulls the chain, causing the sprocket and output shaft to rotate. 3.Rack and Pinion Rotary Actuator- Used design for obtaining partial revolution actuation. The cylinder drives a pinion gear and the rack is an integral part of the piston rod. The angle of rotation depends upon the stroke of the cylinder, rack and the pitch circle diameter of the pinion.

Types of Hydraulic Cylinders/:

Hydraulic Cylinders are of the following types: 1. Single-acting cylinders. 2. Double-acting cylinders. 3. Telescopic cylinders. 4. Tandem cylinders. 1.Single-Acting Cylinders Piston Seal Piston Rod

Extension Graphic Symbol

Retraction Barrel Port According to the type of return, single-acting cylinders are classified as follows: a. Gravity-return single-acting cylinder. b. Spring-return single-acting cylinder. a. Gravity-return single-acting cylinder:

Figure :Gravity-return single-acting cylinder: (a) Push type; (b) pull type b. Spring-return single - acting cylinder. Working- Single Acting Hydraulic Cylinders Push Action Pull Action Oil to extend, Spring Oil to retract, for return Spring to extend

2.Double-Acting Cylinder:

There are two types of double-acting cylinders: a. Double-acting cylinder with a piston rod on one side. b. Double-acting cylinder with a piston rod on both sides. a. Double-Acting Cylinder with a Piston Rod on One Side

Graphic Symbol b. Double-Acting Cylinder with a Piston Rod on Both Sides

Graphic Symbol 3. Telescopic Cylinder : used when a long stroke length and a short retracted length are required. 4. Tandem Cylinder

Used in applications where a large amount of force is required from a small-diameter cylinder. Cylinder Cushions

Prevention of shock due to stopping loads at the end of the piston stroke, cushion devices are used. Cushions may be applied at either end or both ends. Cylinder Cushions (Cont.)  Cylinder Force, Velocity and Power The output force (F) and piston velocity (v) of double-acting cylinders are not the same for extension and retraction strokes. Hydraulic Cylinder Calculation – Extending

Retracting

Power developed by a hydraulic cylinder (both in extension and retraction) is,

Power =Force ×Velocity =F* V Cylinder Mountings- Selecting a particular mounting is depends on whether the force applied is tensile or compressive. Alignment of the rod with the resistive load is another important consideration while selecting cylinder mounts. The ratio of rod length to diameter should not exceed 6:1 to prevent bucking Types- 1. Centre line Mountings- cylinder supported along its centerline. occurs only along axis of cylinder

2.Foot Mountings- cylinder introduce torque under loaded condition

3.Pivot Mounting-when cylinder allowed to rotate while reciprocating