Towing disabled loco

There is a bit of discussion on the GBIX thread concerning 44871's return to Crewe to have a broken radius rod replaced, but I think here is a more appropriate place for my question.

The picture at http://www.national-preservation.com/attachments/dsc_5313-44871-failure-mill-meece-250416-jpg.19692/ shows the loco apparently still in light steam. I understand that it is desirable to have a bit of steam flowing through the cylinders to carry some oil with it. But what happens when the valve gear is out of action? The picture shows the combination lever also disconnected from the crosshead, so presumably the valve on that side is temporarily fixed in position, with the inlet ports open to one end of the cylinder and the exhaust ports open to the other end. What do you do to keep some lubrication to the cylinder, and how do you avoid particles from ther smokebox being drawn into the cylinder?

 

According to the BR "Handbook for Railway Steam Locomotive Enginemen", should the Radius rod break, the affected valve is put in the mid position and secured in that position. (Elsewhere in the book it explains that this is done by wedges/chocks/tightening up the gland.) The Combination lever is disconnected from the crosshead and the bottom secured as far forward as possible to avoid the gudgeon pin. This seems to tie in with the photo of 44871.
The book then goes on to say that the cylinder cocks are left open, and the piston well-oiled by hand-operating the mechanical lubricator before moving off and occasionally during the journey.

 

Excellent answers. Thank you both.

 

I thought that the mechanical lubricator fed oil into the valve chest so that the valve as well as the piston/cylinder gets lubricated. With the valve secured in the mid position, I cannot see how the oil reaches the cylinder, regardless of how much the mechanical lubricator is manually wound round.

 

That's what the book said! Looking at some of the diagrams of piston valves and cylinders, it would seem that in mid-position there is a slight opening at both ends of the valve. And in a diagram relating to one of the mechanical lubricators there are direct feeds into the cylinder as well as the piston valve, although I don't know if that's the sort of lubricator fitted to 4871.

 

The oil doesn't get there through the valve, it is pumped direct to the cylinders, via its own pipework. It doesn't get carried with the steam, like a sight - feed lubricator. If the drain cocks are open, the lubricator will not work, they need to be closed.

Regards,

jtx

 

On many locos with superheat - including all the Stanier types - the oil fed to the valve chests and cylinders from the mechanical lubricator is atomised by steam - provided the taps are closed. There are separate feeds to both ends of the valve chest and the cylinder per side, as jtx says. Different designers used different systems, hence the instructions in the Handbook do not apply in this case.

 

In answer to your final question, regarding how you avoid muck from the smoke box being drawn back down the blast pipes, locos are fitted with snifting valves, these are an anti-vacuum valve, which are held shut by steam pressure when the loco is working, but drop away from the faces when the loco is coasting, or being dragged. These are what give certain classes their characteristic "Chink-chink-chink" noise when coasting (Particularly noticeable on Stanier locos)