Train linkage question.

As I look at train video's on YT, I notice a piece of linkage on what appears to be the main connecting rod. It is on the small end and rotates around a shaft at the end of the main rod. Why is it needed and what does it do?

What loco was it on?

Possibly pne of the linkages in Walschaerts valve gear?

Had it been at the wheel end of the connecting rods, it could have been a speedometer drive, or even the drive for Caprotti valve gear; but without the details, we'll never know.

More details needed for folk to provide a definitve answer.

Howard

I googled "steam locomotive valve gear" and amongst the results was this:

**LINK**

Could you describe it a bit more specifically, Mark, even if you are unsure of the proper part names?

The small end of the connecting-rod is on the cross-head, the sliding part just aft of the cylinder; and in that position might be the drive for the cylinder-lubricator.

Unless you are referring to the polygon of links below the cross-head: in which case it is the combination-lever system that is part of Walschaerts and Baker Valve-gears.

I'm a bit puzzled though by the "rotates around a shaft...". That suggests at the big-end instead, i.e. on the driving-wheel. If it looks like a small box with a cable coming from it and heading towards the cab, it is the speedometer drive. If though a small box with a shaft leading forwards to the valve-chest above the cylinder, it would be as Howard says, the drive to the cam-shaft in Caprotti valve-gear.

If instead a crank on the driving-wheel and outside of the connecting-rod and coupling-rod, it is the primary drive for Walschaerts and Baker Gear.

It is on the left wheel on the Wiki picture.

Edited By mark costello 1 on 11/05/2023 18:44:59

That crank arm provides the drive from the BIG end to the Expansion Link of the Walschaerts valve gear.

The LITTLE end is at the end of the Piszton Rod, and carries the combination link.

And not being a steam manso open to corrections to my terminnology

Howard

It's a return crank and provides a secondary, out of phase, drive to the valve rod via a combination lever. The primary, in-phase, drive is provided from the crosshead via the other end of the combination lever.

Andrew

Since we are talikng valve gear, has any one identified the valve gear on the Brussels tram engine which appeared in this week's episode of the TV show which attempts to reach the Scottish border by steam power ? The gear appears to be a bit like Walschaerts (has a combination lever) but the details at the expansion link end are not really visible and may therefore have a cunning twist.

Thanks All.