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, 23 October 2014

Summer maintenance

The hoped for rain has not materialised !  Flow from the spring is stuck at 0.85 lps.  So with the start of generation for this 'water year' not looking imminent, I'm going to back-track to  August to say something about the yearly maintenance done then.

It was interesting to see what effects one year of operation had had. Impressively there was no wear detectable on any of the nozzles or runner buckets and I put that down to silt mostly dropping out in the header tank, from which about half a cubic metre had to be bucketed out.

I had been concerned that silt might also collect at the bottoms of the upstand pipes leading to each Powerspout nozzle.  To clear the pipes through, the following arrangement was used but from the colour of the discharge, it didn't look as if much silt had collected.

The only serious concern evident on dismantling the turbine was galvanic corrosion going on between the aluminium bulkhead and the stainless steel dump load element, and also where the stainless self tapping screws secure the plastic shell to the bulkhead:

Whilst none of this corrosion would likely have caused failure in the near future, certainly it would have needed attention eventually and I decided to replace the bulkhead with a stainless version.
Michael Lawley in New Zealand was immensely helpful as ever and sent me the CAD drawings to get the replacement cut.  I had never had any experience of laser cutting before so the accuracy which is possible, - to 0.2 mm, astounded me.  

Here is the finished article after refitting in the casing, using M5, socket-head machine screws rather than the original self tapping screws, and a 1" BSP stainless nut, which has a 'captive' O-ring behind it, to hold the heater element: (the bulkhead cost £60 plus £12 VAT)

To complete the annual overhaul, a new set of bearings was put into the bearing block.  Ever helpful again, the EcoInnovation instructional video on this was first class.

That's enough for this post.  I'll add a few other snippets discovered during maintenance in the next.

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