Main Steam Pipe Release Valve Outlet

When Sentinel 7109's regulator is closed, it blocks the steam supply pipe to the engines. With a four to one reduction ratio between the engine speed and the axle speed, this will provide what's called 'Engine Braking' (Big time!).

To prevent things stopping too abruptly, a release valve is provided that opens the main steam pipe to atmosphere when the regulator is moved back to the right beyond the closed position.

Release Valve (at the bottom)

On the regulator handle is a 'lump' containing a spring and a ball. On the housing is a hole which marks the regulator closed position. When the regulator is closed, the ball notches into the hole to indicate closure. The regulator handle then has to be pulled back beyond the closed position to open the release valve.

I had to shape a 1/2" pipe to fit around the main steam pipe and through the original hole in the footplate.

There were two challenges:
(1) Having used a union at the top end of the pipe, I found the nut used to tighten the union fouled the nuts holding the main steam pipe end fitting in place. I thus had to add a short extension to drop the union out of the way.

Elegantly shaped Release Valve Outlet Pipe

(2) The hole in the footplate was under the boiler cladding such that the lower pipe end would not fit through the hole. I thus had to cut the pipe, add a coupling and feed the lower end of the pipe up from underneath. I cut a tapered thread on the top section of pipe and screwed it into the coupling very tightly. I cut a parallel thread on the pipe from below such that it would be the section that came out of the coupling if it ever needed to be removed in future. (The coupling itself will not fit through the hole).

Lower section of pipe below the footplate

'The End'

I've put a round-edged coupling on the end of the pipe to prevent me from gouging a lump out of my head whilst passing underneath!