constructed from high strength material and then generally not an integral part of the rotor may be preferred particularly for machines designed for producing lower gas pressures the use of plain or sleeve type bearings is preferred for bearings 59 61 a and 61 b these being lubricated from the available pressurised oil supply however needle bearings could be alternatively employed fig7 is an axial view section of the rotor 18 internal gear 20 engages with stationary gear 22 axis 71 is the fixed centre of rotation of the eccentric shaft not shown axis 25 is the orbiting centre of rotation of the rotor the distance between these two centres being the eccentricity u201c e u201d as shown u201c r u201d is the dimension from the rotor centre to a rotor apex as shown holes 79 feed oil to the slots containing apex seals 19 the cross hatched outer perimeter axial face 83 slidably engages in close proximity with the adjacent end plate the axial face 83 can be constructed to possess a radial small dimension because it is not required that side seals are fitted into any of the axial faces as is the convention a very effective sealing of the working chambers being achieved in this invention by the oil flooding which exists between the end plate surfaces and face 83 as.