Sanding Gear (1)

After a few months of apparent inactivity with Sentinel 7109, things have actually been happening (although much of my time of late has been spent defining safety critical operational roles and training material for Midsomer Norton); the first of these is the fitting of a replacement sandbox pipe at the off-side front.

For ages, there have been three original pipes painted and ready to fit to feed sand from the four sandboxes to the rails; however, the fourth one had disappeared some time ago or so I thought. I'd searched and searched, convinced that the fourth one existed, but finally resigned myself to having to make a new one, flange and all.

Eventually, on close examination of the sand box itself, I found that there was a flange still in place underneath with clear evidence of a pipe having been broken off from it.

So I'd been wrong; the fourth one hadn't existed after all.

New Sand pipe (1)

The new pipe is made from mild steel with a longitudinal weld, i.e. not malleable iron or cold-drawn seamless steel. A 3/4" BSPT thread needed to be cut to fit the flange on one end before bending to shape. (It's difficult to clamp a bent pipe for thread cutting!).

New Sand pipe (2)

After shaping into a mirror image of the near side front pipe using a 12 ton hydraulic pipe bending machine, the lower end was cut diagonally to feed the sand into just the right place.

Finally it was screwed into the threaded flange still attached to 7109. (28 tons of solid metal certainly held the flange tightly in place!).

There's much more to come on sanding gear, particularly working out how the levers need to operate the four boxes.

Sentinel 7109's Sandboxes

There are not unusually four sandboxes, one at each corner. However, this is where the fun starts regarding how they are operated.

An arm on the top of each box rotates a shaft when pushed or pulled. The shaft extends to the bottom of the box and moves a flap over a hole to allow or prevent the sand descending through the hole to the track.

The two front and the near-side rear boxes are all operated by one lever, the one to the left of the reverser lever. Oddly, the off-side rear box is operated by another lever, the one to the right of the reverser lever, via a vertical shaft.

LH lever operates 3 boxes via a cross shaft behind the boiler and below the coal bunker.
RH lever operates the offside rear.

Working on 7109, I sometimes wonder whether it really was a prototype with all the usual bodges to make a saleable first-off actually work. I can't see any reason why the same lever could not have been made to operate the offside rear as well. Is there anyone out there who knows better?

The sandboxes are heavy castings; one box's mechanism in particular had seized due to rust combined with sand over a long period.

Flap seized over the hole (the fluid is diesel to attempt to free it)

One attempt to free the mechanism freed only the end of the flap!

And so began the box repairs. Access is only via the small filling hole on top; a gas-axe being the only practical way to remove the innards!

Sandbox "remodelling" begins!

The front two and the near-side rear sand-box operating arms are having to be recast due to breakage or absence.