THE HISTORY OF VANE COMPRESSORS
What is a vane compressor and how does it work?
A rotary vane compressor is a positive displacement machine that uses an eccentric rotor placed within a cylinder. The rotor has slots along its length, each slot contains a vane. The vanes are thrown outwards by centrifugal force when the compressor is running and the vanes move in and out of the slot because the rotor is eccentric to the casing. The vanes sweep the cylinder, sucking air in on one side and ejecting it on the other.
Rotary vane compressors use either carbon vanes for low pressure oil-free duties, or asbestos/steel vanes for lubricated duties. Various asbestos (and similar performance asbestos free) compounds are widely used for low pressure applications, up to about 3 barg. Over and above this pressure, the vanes are steel or cast iron because of the substantial bending forces present when the machine is running.
Where did the vane compressor come from?
One of the first vane type machines was the Lemielle exhauster, invented in France during the early 1800's, and widely used in Belgium to provide ventilation for collieries. The design of this large machine used hinged vanes mounted upon the surface of a rotating drum which was in turn mounted eccentrically within a casing. The vanes were mechanically controlled to ensure semi-contact with the outer casing. It was then only a single step to replace the hinged vanes with sliding vanes.
The principle of the modern sliding vane compressor dates back to the early 1900,s when an American by the name of Robert Blackmer invented the first rotary vane pump.
The oil injected sliding vane compressor was first produced by an Italian manufacturer called Pneumofore SPA in the late 1920's and the product has been developed through the years by various manufacturers worldwide to provide a wide range of diverse models.
In the UK and towards the end of the 1940's, one Major P.C. Bird patented a new type of lubricated vane compressor under the tradename 'Oilvane'. Alfred Bullows acquired an exclusive licence from Major Bird, and after a period of development the first Hydrovane compressors shortly followed.
What is the difference between a lubricated vane compressor and an oil free vane compressor?
The obvious answer is that on produces 'oily' air and the other produces oil-free air. However, the differences are much greater than this.
Dry type vane compressors can only operate at low pressure, due to the extremely high discharge air temperatures. The vane material is usually carbon based with additives to make the blade more shock resistant. The clearances are critical because of the thermal differential between a cast iron (or steel) rotor and the solid carbon vanes. With discharge temperatures approaching 120 deg C, the vanes can easily jam.
Should the carbon vane stick inside its slot, then the volume delivered and mechanical efficiency drops, the discharge temperatures reduce and the vane frees itself. If the vane jams in the extended position, the bending forces will break the back of the vane and the machine will quickly come to a grinding halt.
Lubricated vane compressors are either drip type, or oil flooded. Drip type compressors and exhausters have a small pump affixed to the non-driven end of the rotor shaft, this pump then delivers a calculated number of drips to the sliding vanes. The drips of lubricating oil remains with the compressed or exhausted air and must be removed (if necessary) using additional filtration.
The oil flooded vane compressor operates in the same way as the oil flooded screw compressor and uses a separator system to remove the bulk liquids so that the system downstream does not become too contaminated. Because the heat of compression is absorbed by the oil, the heat can easily be removed using an oil cooler. Typically the air temperature measured at the discharge port of an oil injected rotary vane compressor is about 30 deg C above ambient air temperature. This drops to only 8 deg C above ambient after it has passed through and air blast aftercooler.