# Types of Lifting Machine

## Lifting Machine:

Now, there are many types of lifting machines that are available in the market. But the basic principle, on which all those machines are based is the same. It will be interesting to know that engineers who have designed these machines have tried to increase the velocity ratio of their respective lifting machines.

A little consideration will show that if the efficiency of a machine remains almost the same, then an increase in the velan opacity ratio must increase its mechanical advantage. The increased mechanical advantage of a machine means the application of a smaller force to lift the same load or lift a heavier load with the application of the same force.

## Types of Simple Lifting Machine:

The following lifting machines are important from the subject’s point of view are given below:

### Simple wheel and axle:

In above figure shows that a simple wheel and axle in which the wheel A and axle B are keyed to the same shaft. The shaft is mounted on ball bearings, order to reduce the frictional resistance to a minimum. A string is wound round the axle B which carries the load to be lifted. A second string is wound round the wheel A in the opposite direction to that of the string on B.

Let D = Diameter of effort wheel
d = Diameter of the load axle
P = Effort applied to the lift the load.

One end of the string is fixed to the wheel, while the other is free and the effort is applied to this end. Since the two strings are wound in opposite directions, therefore a downward motion of the effort (P) will raise the load (W).

Since the wheel as well as the axle are keyed to the same shaft, therefore when the wheel rotates through one revolution, the axle will rotate through one revolution. We know that displace of the effort in one revolution of effort wheel A.
= πD

### Differential wheel and axle:

It is an improved form of simple wheel and axle in which the velocity ratio is intensified with the help of load axle. In above figure shows that a differential wheel and axle. In this case, the load axle BC is made up of two parts of different diameters. like simple wheel and axle, the wheel A and the axies B and C are keyed to the same shaft which is mounted on ball bearings in order to reduce the frictional resistance to a minimum.

### Weston’s Differential Pulley Block:

It consists of two blocks A and B. The upper block A has two pulley (P1 and P2) one having its diameter a little larger than that of the other. The pulleys turn together as one pulley, both of them behave as one pulley with two grooves. The lower block B also carries a pulley, to which the load W is attached.

### Geared Pulley Block:

It is an improved form of a differential pulley block in which the velocity ratio is intensified with the help of gears. A geared pulley block consists of a cogwheel A, around which is passed an endless chain. A smaller gear wheel B known as pinion is keyed to the same shaft as that of A.

### Worm and Worm Wheel:

It consist of a square threaded screw, S known as worm and a toothed wheel known as worm wheel geared with each other. In above figure shows that a wheel A is attached to the worm, over which passed a rope as shown in the figure. Sometimes a handle is also fixed to the worm. A load drum is securely mounted on the worm wheel.

### Worm Geard Pulley Block:

It is an improved form of worm and worm wheel in which the velocity ratio is intensified with the help of a pulley block. It consists of a square threaded screw S and a toothed wheel. One end of the string is fastened to the frame. This string passes round the load drum B and then over the pulley A . The other end of the string is also fixed to the frame.

### Single Purchase Crab Winch:

In single purchase crab winch, a rope is fixed to the drum and is wound a few turn round it. The free end of the rope carries the load W. A toothed wheel A is rigidly mounted on the load drum.

### Double Purchase Crab Winch:

A double purchase crab winch is an improved form of a single purchase crab winch in which the velocity ratio is intensified with the help of one more spur whell and a pinion. In a double purchase crab winch, there are two spur wheels of teeth T1 and T and T3 as well as two pinions of teeth T2 and T4.