Safety Valves (2)

My last look at Sentinel 7109's safety valves was about two years ago. Then I'd initially mounted them on the first version of a manifold constructed from heavy duty steel pipe fittings.

First attempt

All seemed good at the time but a number of factors began to come to light that meant some changes had to be made.

1. I wasn't sure that the metal of the threaded nipples connecting the steel fittings was strong enough and may have been made from 'Blue band' rather than 'Red band' grade pipe. (Red band pipe has a thicker wall and is rated suitably for the Sentinel boiler's wet steam conditions. Blue band is not good enough).
   I replaced the connecting nipples with heavy duty hex nipples which are much stronger.
   
   
2. I was concerned that when I removed and refitted the safety valves for the boiler's next and any subsequent hydraulic tests, the thread would not make as tight a joint as the first time. They would also need to be removed to fit the boiler top cover.
   I inserted a 3000 psi rated union and mating nipple between the manifold and each safety valve body. The union is designed to be undone and also enables the safety valve to be correctly orientated so its exhaust pipe would align with its hole in the cab roof when refitted.
   This does make the assembly taller but practical!
   
   
3. I had assumed that I could obtain a steam supply for the vacuum brakes, the whistle and the pressure gauge from the four-way manifold used to feed the superheater. However, with all the other pipework in place, it was too inaccessible particularly to reach an isolating valve in that location.
   I thus decided that the safety valve manifold would have to include the steam supplies for the vacuum, whistle and pressure gauge.
   
   
4. At least one of the safety valve outlet pipes would have to pass through cab roof support girders. Not good!

Here's the result. Hex nipples hold it all together. The 3000 psi unions sit below the safety valve housings. The two 'L' shaped fittings are now 'T' shaped so the extra outlets can be taken from each of the new 'arms'. The vacuum supply is downwards from the left 'T' and the whistle and gauge supply horizontally from the right 'T' to an isolating valve.

The exhaust outlets now straddle the roof support girder!

Not cricket wickets!

There's more to do to prevent the pipes rattling in the cab roof holes and to ensure it all lines up if taken apart and reassembled.

In-Cab Boiler Feed Pump Drain Cocks

Having fitted Sentinel 7109's cab boiler feed pump some time ago, there was still some pipework to be completed. I'd constructed the feed from the water tank and the steam exhaust but there was more left to do (and still is!). This article deals with the drain cocks.

There are four drain cocks, one at each end of each of the twin steam cylinders, as in the photo on the right. However, in their original form, they were a mess waiting to happen as they would spew oil and water out on to the cab's ledge.

I decided that they needed drain pipes so that the outflow could end up somewhere more sensible.

3/16" Copper pipe is readily available for automotive brake systems. In preparation, I brazed compatible fittings on to the drain cocks as shown.

The Copper pipe is easy to bend by hand and the final result looks quite elegant.

The four pipes are taken through holes in the ledge and secured to the steam exhaust pipe with tie-wraps. (Let's hope they stand the heat!).

Finally the outlets are strapped to and just above the steam exhaust outlet. There is a thread on the end in case the exhaust needs to be extended later.

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!

Apologies

Sentinel 7109's blog will be back up and running again soon. My mother died recently and it's rather taken my mind off the usual things.

Rest assured there is much going on behind the scenes with high-spec pipework, low-spec pipework, vacuum fittings and sandboxes.

As the computer says... Please wait!

In days gone by, the BBC would have provided an interlude as follows: https://www.youtube.com/watch?v=jUzGF401vLc

The phone's engaged!

Full Vacuum Ahead!

Strictly this should be Vacuum Braking (14) Implementation (8), however, I needed a more vague heading!

Two new items have appeared on top of Sentinel 7109's cab roof: to the left is Nigel's coffin and to the right is a rather fetching and elegant periscope (respectfully looking away from the coffin!).

A Rail-hearse in the making?

The periscope, in a truncated form, will double as the vacuum ejector's exhaust outlet.

Up Periscope!

And finally, the boiler now has a leg to stand on. In fact, it's the beginnings of the blow-down valve pipework. I'd been checking out the four boiler washout plug holes around the base; one is used for blowing down the accumulating sedimentary detritus.

Caption competition?

The 'leg' showing will be red-band steel pipe to withstand the boiler pressure.

Meanwhile, in Steam Railway magazine (issue 441), there is an article about Sentinel 7109 in its 'In the Works' series. Any content in common with my blog articles is entirely coincidental, of course!