Feeding oil from OD to shaft centre

The radial holes in the shaft act as a centrifugal pump and will try to pump opposite your desired flow direction. This crude pump will produce a maximum pressure ( at zero flow) equal to the kinetic or velocity energy energy of oil moving at the shaft OD velocity. Correct for the specific gravity of the oil to get actual pressure. This is the additional pressure that will be needed to create the flow in the opposite direction you desire. To that, of course must be added the calculated friction losses to achieve your desired flow rate.

Without actually doing the calculations it appears that the additional pressure you need is on the order of 0.1 to 0.2 bar; likely an order of magnitude less than the friction losses in your system. Still enough to take account of in your design.

Ed Weldon

I already send an answer which for reasons I do not know did not appear.

Computations of both centrifugal forces and losses in the radial ducts lead to about 0.5 bar based on a rough calculation. For better reserves a pressure of 4 bar seems to be sufficient. The problem you will be confronted with is the sealing between stator and shaft.

It is one positive aspect the friction will not lead to a local high temperature (penalising seals life) due to the oil flow.

If you can afford a labyrinth seal is friction free but has a supplementary flow so that depending on the design you have at least 2 choices.

Thanks ED,

Yes, the shaft bores work as a pump in the 'wrong' direction. However I also feel that the value is tolerable, my calcs also come to about 0.2 bar.

Thanks to you as well, Nick.

You brought up a good point about a labyrinth seal. I will consider that. Likely that is needed, at least in a crude form with some side abutments. Good point.

Regards to all.