Stirling Single Safety Valve Bonnet – round or oval?

[mjc43Participant @mjc43]

I was studying my Reeves casting for the Stirling Single 5″ gauge safety valve bonnet trying to decide the base way to tackle it and it struck me that it didn’t look round. In fact it looked like the further you went down from the round bonnet top, the more the cross section appeared to be oval. I put it on a mandrel and used the DTI in the lathe to plot its deviation for various slices top to bottom and the measurements reveal two distinct peaks and two troughs per rotation at th bottom, decreasing in amplitude until circular near the top.

The drawings don’t have a projection that would reveal whether this lower oval profile is intentional or not. Unfortunately I didn’t think to climb up on NRM Stirling Single and measure it when I was up there a couple of years ago.

If the cross section was circular all the way down I could use a lathe cutting too to sort the surface out but if oval I’m stuck with files and abrasives.

Anyone know the truth of the matter? Is it intentional or a feature of the casting?

Mike

[WearyParticipant @weary]

Hi Mike,

Can’t answer  your question with certainty I’m afraid, but I suggest that you ask your question over on Model Engineering Clearing House (under ‘General Chat’ heading) as at least two of the members have built Stirling locos and others are familiar with the ‘singles’.

There is a detailed ‘build thread’ here that may give some insight.

Phil

[Author]

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