THE HISTORY OF ROOTS BLOWERS
What is a Roots Blower and how does it work?
A Roots compressor/blower is a positive displacement machine that uses two or more rotating lobes in a specially shaped cylinder, usually shaped like the figure of 8. The lobes intermesh with each other using timing gears and suck air in from one side of the figure of 8 to deliver the air on the other side.
There is no actual compression ratio built into the machine, it is simply an air mover. Compression is caused because the induced air is forced into a closed conduit, thereby causing the atmospheric air becomes pressurised after it has left the Roots blower.
The rotating impellers intermesh quite closely, but contact is avoided by using precision timing gears. Although these gears are splash lubricated, because they are external to the cylinder barrel, the machine provides oil free air.
Where did the Roots compressor come from?
The principle of the Roots compressor/blower was discovered by two brothers in the mid 1800's. They were Philander H. and Francis M. Roots, joint owners of a woollen mill in Connersville Indiana. The positive displacement blower was named after them and the original Roots Blower Company was formed, however the name is widely used by various manufacturers to describe a generic type of compressor/blower.
The Roots blower was exhibited in Paris during 1867 and was looked upon (at the time) as a potential answer to the difficult problems of deep mine ventilation.
About forty years later a rival blower manufacturer was formed in the same city, called Connersville Blowers. The companies competed with each other until 1931 when they were both bought out by a third party and merged.
What is a blower used for?
Low pressure compressed air has as many applications as factory line compressed air has. One of the main uses is for pneumatic conveying. That is 'blowing' powders down pipes so that the powder flows in the same way as a liquid. Pneumatic conveying is usually carried out at fairly low pressures, between 5 psig at 15 psig depending upon the nature of the material being conveyed.
The blower forces low pressure air into the pipe and the materials being conveyed are introduced using an airlock feeder. This item is designed so that the low pressure compressed air can't escape, but at the same time it allows the powders or granular materials that are intended to be pneumatically conveyed, to be dropped into the moving air stream.
At the other end the conveyed materials must be removed. This is accomplished using a cyclone type separator, the compressed air is slowed down to such an extent that the material being conveyed drops out of the air stream to fall through a chute affixed to the bottom of the cyclone.
Vast numbers of Roots type blowers are used on tankers, for road transportation purposes.