3 inch Burrell

[burrell2023]

Neural to me means the die block in the middle so not much movement on the valve.

I can’t seem to get the linkage to be vertical in both positions, or maybe it shouldn’t be..I’m just trying to remember how I did the Allchin.

[burrell2023]

[ettingtonliam]

Its a while since I did his myself, and the memory isn't so good. The experts on valve gear on this site don't seem to scroll down as far as 'Road Steam' so you might try repeating this on 'What I've done today', especially with these latest photos.

[ettingtonliam]

I've just recalled that in full size traction engine practice when the valve was being set cold, allowance was made for the change in length between the cylinder and the crankshaft for boiler expansion at working temperature. It probably won't be much in a model, but expansion of a copper boiler will be measurable.

[burrell2023]

Yes I agree, I think that would be more adjusting the valve only.

If I could confirm if the lifting links should be perfectly vertical when die block is in the centre of the expansion link and the crank either up or down meaning piston would be central in the cylinder.

Something like this, excuse the dread duo sketch .

[uuu]

I don't think the lifting link has to be vertical.

I can't find evidence of your arrangement, but a locomotive example below is not vertical:




And here's another, not quite upright:



Wilf

[uuu]

And - here's an illustration from Don Ashton's page (web.archive.org/web/20190919220645/http://www.donashton.co.uk/html/stephenson_s_gear.html):



Where he says: "...The illustration shows wrong thinking on two scores. Firstly, the square symmetry of the reversing arrangement cannot accommodate angularity errors at all..."

And - here's the killer quote: "...Therefore the lifting link is highly unlikely to be vertical, though few traction engine designers seemed to realise this!..."

Wilf

[burrell2023]

Thanks very much Wilf, that gives me a bit more confidence that I’m possibly in the ball park.

[Jim]

I found with the Burrell I needed to do a fair bit of tweeking with the valve cover off along  to ensure the slide valve was opening evenly. From memory I also removed the fron cylinder cover to check the clearances and valve events. I didn't make any allowances for boiler expansion as the changes were too small to effect the valve events in any meaningful way.

This is a photo of the general layout of the Burrell's valve rods.

[burrell2023]

Thank you very much 👍