The set up

The set up
5.46mm jet delivering 0.68 l/s to the pelton which is rotating at 900 rpm and generating 135 watts into the grid.

Thursday, 6 July 2017

14,448 hours

A couple of days ago I noticed the Powerspout wasn't sounding right. Here is an audio clip of the shaft coming to a stop after shutting off the flow.

The bearings have not been changed since 10th November 2015 and that's 14,448 hours ago. The turbine has run continuously for all of that time bar stoppages for nozzle changes and one de-silting of the header tank.  Clearly the time to change them had arrived and in this post I want to tell how things looked after such a protracted period of operation.

The bearings at each end of the bearing housing looked completely unremarkable; a small amount of the SKF Lesa 2 grease I have been using was evident at both ends, more or less equally distributed between the two ends, and was only a little grey in colour at the pelton end:

My greasing regime has been 4 pumps from a small grease gun once a month (0.8 grams / 1.4 ml per month).

From the encrusting on the length of shaft that sits in the 'top hat water flinger', it was evident that quite a bit of water penetrates into the 'top hat'. The picture below of the wet side of the SOG seal shows a tide mark to half way up it suggesting that water enters more quickly than it can quickly exit from the drain hole: 

Crucially however, there was no evidence whatsoever of water getting past the lip of the SOG seal, and had it done so, the notch cut in the bearing housing to allow it to drain downwards was fully patent and not blocked with grease which had passed through the pelton-end bearing.

The bulkhead showed where water had been striking it and it was pleasing to see this was a mirror image of the splash pattern seen on the front glazing, - indicating that nozzle alignment directing the jet onto the splitter ridges of the cups was pretty good:

The old bearings were taken out and thoroughly examined by dismantling them.  At first there seemed to be little damage to explain the rumble that had indicated the end of their working life, - but on examination with an eye glass there was spalling in the groove of the outer race and this pit was evident at one point in the groove of the inner race:

Spalling* in the groove of the outer race: 

These bearings were SKF units (made in China) as supplied by EcoInnovation. What I have installed in their place are SKF E2 energy efficient bearings which I do not intend to grease at all, - relying on their factory fill of grease to last for their entire working life.

EcoInnovation encourage Powerspout owners to change the bearings every year and this is undoubtedly the right advice: 14,448 hours is 4 months short of 2 years so it is better to stick to an easily remembered 12 month regime.  The exercise described here of pushing the boundary to see how long I could get bearings to last was just an experiment - and it has been an instructive one too.

...and here is what the shaft SHOULD sound like as it comes to rest.

*Spalling is when tiny flakes of material are broken off from the wearing surfaces of a bearing and become deposited in the grooves where the balls run making them no longer smooth.

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