Since this air is unable to escape, it raises the air pressure P inside the chamber. When this pressure reaches a value such that
P = W/A.

The upward force exerted by the chamber balances the load resting on the top. The load now floats clear of the ground slightly. As soon as that happens, leakage of the chamber to the outside takes place due to the pressure difference between the air inside and the atmosphere. This leakage air is replenished by the pressurised air which is being continuously supplied to the chamber. The load is now floating free of the floor and thus can be easily moved in any direction by applying a very small force . This force is typically of the order of one or two kg per ton of the load. The hovercraft is one well-known example of passengers and cargo movement based on the above principle.

• Free Path Air Cushion Mobility Systems.
• Fixed Path Air Cushion Mobility Systems.

This system is used for moving around heavy, bulky or akwardly shaped objects such as machine tools, heavy electrical transformers etc.,or those requiring smooth and accurate positioning during production, assembly or storage, such as aircraft engines, fuselage parts, or even complete aircraft.

The basic building block of this system is a load bearing member usually of circular cross-section on its underside commonly referred to as air bearing, air caster, etc. by their respective manufacturers.

As explained previously, the incoming compressed air first floats the Air Caster slightly off the ground and then starts leaking out through the leakage gap between the bottom seal and the floor.
Since this air must be replenished from the compressed air supply, it is advisable to keep this gap as small as possible, since other things being equal, the quantity of leakage air is directly proportional to the size of this gap. Thus, the smoother the surface of the floor, the smaller the gap can be, without introducing friction between the seal and the floor. For occasional movement over a relatively rough surface, a thin metal sheet can be temporarily laid over the area where the load is required to be moved, so as to reduce the air consumption.

For practical applications, these individual air bearings are usually combined in a number of ways.

A minimum of three bearings are required to provide a stable platform for the load but it is usual to combine them in a group of four or six or even more.

The one shown can carry a load of over four tonnes and can easily be moved around by a single operator. Other sizes and carrying capacities up to 80 tonnes are in existence. Theoretically, with suitable arrangements there is no limit to the size and weight of a load that can be moved around on a fluid film.

In certain applications for conveying or positioning materials the air cushion principle is utilised in a different manner.

Here a smooth table surface is laid out over the path which the object or objects are to follow. Air under pressure is supplied through a plenum which is mounted under this table and this air comes out through the holes provided at regular intervals over its surface.

The moving load which should have a flat underside such as sheets of paper, glass, metal etc.. or be of such shape as to prevent the escaping air from the table to pass directly through it e.g. a rectangular carton or an upturned tumbler. This escaping air then forms a cushion as explained earlier, and the object which is now literally floating on air can be moved around anywhere on the table surface with but negligible effort and very smoothly too.
The moving load is thus handled very gently as compared to a belt or roller conveyor and is thus popular in industries such as garments stretching and cutting tables, paper handling equipment, food processing, etc. shows schematically some representative examples of this type of air conveying system.

Materials on the air table conveying system can be moved about either by hand, mechanically, or gravitationally, by giving a slight inclination say 50 degree in the direction in it is required to move.

A variation of the air table uses inclined nozzles for exit of the pressurised air instead of vertical openings.

In this system the air flow is utilised both to 'float' the material as well as convey it in the direction of the inclination of the nozzle due to the horizontal component of the force exerted by the escaping air. This method of moving the loads has some advantages, specially for delicate items requiring gentle handling. Even in case of a 'traffic jam' in the path of load movement, no excess force is exerted on the items being moved.

There is however a price to be paid is somewhat larger consumption of air and therefore energy.

The advantages of Air Cushion Mobility Systems over other alternatives used for similar work such as wheeled trolleys, belt and roller conveyors etc. are as follows:

• Low unit pressures: Due to the large supporting area under the load (foot-print), the unit pressures in this system are far lower than those produced by wheeled vehicles, being typically of the order of 1.5 Bar(20 PSI) and rarely exceeding 3.5 Bar(50 PSI). This reduces wear and tear on the shop floor. In fact for some less sturdy floors, this might by the only feasible system for load movement over it.
• Omni-directional mobility: Unlike wheeled vehicles, or roller/belt conveyors a load supported on an air cushion can be moved around in any direction equally easily, forward, backward, diagonally, sideways, or even completely turned around on its own axis. This is specially used when maneuvering heavy loads in restricted quarters.
• Safety of operation: Since the load is lifted just a few millimeters off the ground, and the gap between the bottom seal and the supporting surface is less than a millimeter, it results in enhanced safety, both for operating as well as other personnel in the vicinity. In case of a failure of compressed air supply for any reason, the load gently sinks back to the supporting surface, the air trapped inside the air casters or the air plenum chamber acting as a damping medium as it slowly leaks out.

  In conclusion, one may say that air cushion mobility systems for moving objects in various industries are versatile, safe, proven and cost effective methods.

  The coming years will thus see their wider adoption in Indian industries, more so in its innovative and hi-tech sectors.