It is well known that a mixture of fluids having different densities may be separated from one another through use of a centrifugal separator. One specific use of such a separator is in the separation of oil from gas vented from a crank case forming part of an internal combustion engine.
With regard to this specific use of separators, there can be a tendency for the high pressure gasses found in the combustion chambers of an internal combustion engine to leak past the associated piston rings and into the crank casing of the engine. This continuous leaking of gas into the crank case can lead to an undesirable increase of pressure within the crank case and, as a consequence, to a need to vent gas from said casing. In large commercial vehicles, vented gas is generally reintroduced into the inlet manifold of the engine. However, the gas vented from the crank casing typically carries a quantity of engine oil (as droplets or a fine mist), which is picked up from the reservoir of oil held in the crank casing. More specifically, gas flowing between an engine cylinder and the associated piston tends to pick up lubricating oil located on the cylinder wall. Also, condensing of oil vapour by an engine's cylinder block cooling system generates an oil mist in the crank case.
In order to allow vented gas to be introduced into the inlet system without also introducing unwanted oil (particularly into a turbocharging system wherein the efficiency of the compressor can be adversely affected by the presence of oil), it is necessary to clean the vented gas (i.e. to remove the oil carried by the gas) prior to the gas being introduced into the inlet system. This cleaning process may be undertaken by a centrifugal separator, which is mounted on or adjacent the crank case and which directs cleaned gas to the inlet system and directs separated oil back to the crank case.
There are a number of problems associated with some prior art ALFDEX™ separators. These problems can be considered in three broad categories.
First, the fluid pathways through the separator give rise to pressure losses which adversely affect the flow capacity of the separator and, consequently, the size of engine with which the separator can be used.
Second, the arrangement of some of these prior art separators is such that, under certain conditions, cleaned gas can become contaminated before leaving the separator.
Third, certain manufacturing techniques and construction features associated with these prior art separators can lead to assembly difficulties and/or reliability problems.