AIR CASTERS

The Investigation Of Air Casters



Table of Contents

Chapter One: Air Casters3

Chapter Two: Methodology4

Chapter Three: Types of Air casters10

Rigid Air Bearing10

Skirted Plenum or "Hovercraft"11

Compliant Air Bearing11

Airfloat Air Bearing12

Floors13

Floor Surface Requirements13

The Finger Test and Floor Fixes15

Floor Flatness15

Steps16

Ramps17

Cracks and Expansion Joints17

Porosity18

Chapter Four: Literature Review20

Pneumatics and Air Casters20

References23

Chapter One: Air Casters

An air caster is a pneumatic lifting device used to move heavy loads on flat, non-porous surfaces. Its operation is similar to a hovercraft, in that it uses a thin layer of air as a way to float a very small distance off the ground. Compressed air enters an airbag shaped like a torus (or donut), when the bag is filled two things happen(Parker Wolf Block 1990 pp.112-119):

1. The bag creates an airtight seal with the ground, thus accumulating greater amounts of air with no means of escape.

2. More and more gas is forced into space inside the torus center, eventually pushing its way under the airbag as a thin film of air lifting the whole unit off the ground.

The compressed air is forced under the airbag, pushing it and the load less than a millimeter off the ground.

Chapter Two: Methodology

Air casters are a means of making scenery move by floating it on a thin cushion of air. The operating principle is similar to that of a hovercraft: a plenum of air under the load is maintained at a higher pressure than the external air. Air continuously escapes from the plenum, lifting the load ever-so-slightly off the ground. (www.stagecraft.org)

A typical air caster design uses an air bladder, frequently shaped like a torus (a donut). Reduced friction and omni-directional transfer allow the operator to precisely place and align the air bearing in a limited work space. The low profile of the Load_Module_Systems air caster load module requires less than 3-inch (76mm) clearance. An air caster will not damage floors and expensive reinforcement is usually not necessary.

Because we use only basic pneumatic components such as air regulators and hoses, our products are not only reliable, but will operate in most environments unlike some other types of heavy load handling systems. When air is not being supplied to the air caster, the bladder is empty, and the (www.asesystems.com) load rests on some other support. Frequently, this is built into the air caster unit, as in Figure 1.Some air casters, however, do not have a built-in air-off support; in this case, it must be built in to the structure of the platform instead. Fortunately, this is not difficult; it can be done by placing a support on the platform or other scenic unit that is either flush with or extends slightly beyond the depth of the un-inflated air caster. When air is applied, the bladder inflates and presses against the ground, as in Figure 2. This seals off the area inside the torus. The air pressure is then applied to the plenum inside the torus. Once the plenum reaches a sufficiently high pressure, it can lift the load off the ground, as in Figure ...