Friday, 28 August 2015

Preservation Moves in Brazil

After the retirement of the two 7109-like Sentinel locos in Brazil in October 2014, they have now been moved from the Amsted-Maxion Steelworks, Cruzeiro, to a location for safe storage and, hopefully, restoration with future use.
166 (8400) en route (Photo by Bruno Sanches)
167 (8398) ready to unload (Photo by Bruno Sanches)
8398 and 8400 in their new home (Photo by Bruno Sanches)
The new home is at the ABPF - Regional Sul de Minas (Brazilian Association of Railroad Preservation). (For those whose language skills are as apologetic as mine, google can translate pretty well!).

Friday, 21 August 2015

Vacuum Braking (14) Testing (1)

Now things are starting to get interesting. Testing is where you find out what you got wrong and get the chance to put it right.

Putting it right is best done by first privately figuring out how to do it and then showing onlookers what is wrong but apparently instantly coming up with the solution. It's best done this way; nobody notices if you get it right first time!

The first simple test is to show that the vacuum pipework does not leak excessively. (In actual fact, it does not matter if the system leaks but it does matter if it leaks so much that the vacuum ejector cannot suck hard enough to overcome the leaks and pull the train brakes off. This is inherently safe on a loco but undesirable on a carriage or wagon with vacuum brakes).

I sealed the rear vacuum end with the usual blanked-off, dummy coupling.
Blanked-off vacuum hose coupling
I attached the front end to a vacuum brake tester which I constructed about six years ago (much easier than shunting a loco to do the job and much more controllable).
The narrow hose links to the tester shown on the right.

The black vacuum pump is a Seco type SV1040C supplied by Busch and can pull 24 cu ft/min.
The brake tester can evacuate the system to the required level (21" Hg) to exercise the vacuum relief valve and enable the brake lever to perform its function.
Blue brake lever handle with relief valve behind and silencer in front
More detail here
Powering up the tester draws the 21" Hg (left).

Opening the brake valve drops the vacuum (right)
It's much better illustrated with a video: (Also on YouTube).

video
The 'whirring' noise is the tester motor

The tester has a non-return (check) valve such that when it is switched-off, the vacuum is held. In this way, leaks can be detected by watching the time it takes for the vacuum to drop.

Although the tester itself leaks a tiny bit, initially there were obviously some pipework leaks; however after tightening all the pipework unions (all other joints are sealed with Heldite), it was deemed to be satisfactory (with the brake test unit, that is, not the ejector itself - that's another test!).

Monday, 17 August 2015

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.

Friday, 14 August 2015

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.

Thursday, 13 August 2015

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!
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