Tuesday, 27 January 2015

Keeping the Heat In (A Cover-Up!) (2)

Monday 26th Jan. 2015 saw the first attempt at fitting the boiler top cover to the chimney assembly. An earlier article showed what the cover was like before work began on it.
Start of the Boiler Top Cover assembly
There is a rim around the base of the chimney heat shields that supports the centre of the top cover. The cover will then also be supported by six tall spacers sitting on the extended studs protruding from the boiler fixings (there's one just to the left of the LHS superheater tube in the foreground).
Space getting tighter
Having examined the boiler of the only other double engined Sentinel (9622) in the UK, I'm expecting the spacers to be 6.25". However, this is far from the case; they are sitting much higher and the LHS and RHS halves of the cover are not fitting very comfortably.


Some further investigation is needed.

Sunday, 25 January 2015

Getting on a Flap

Just to top-off the previous chimney article, the damper flaps have been added.
Ta Da! Flaps Open...
...Flaps Closed
And the remote controls:
Flap Open...
...Flap Closed (or was it the other way round?)
Still more to do with adding the Chimney Surround to the cab roof and the boiler top covers.

Damping down a fire for a short period can be done either by restricting air flow into or out of the fire (or both). Whilst some air-in damping can be done by adjusting Sentinel 7109's ash pan, Sentinel chose to restrict the air-out mainly by enabling flaps to be placed over the chimneys.

Saturday, 24 January 2015

Parallel Chimneys

My last chimneys article clearly raised some anxiety with Sentinel 7109's co-owner regarding the stresses that would be present in the boiler top plate if the chimney tubes were aligned purely by pushing apart the castings. I had to agree!

The alignment tool showed that the LHS pair of tubes were in fact leaning towards the RHS pair and not in line with the blast as in the photo below (looking towards the rear).
The white dot is the end of the alignment tool's threaded rod
and slightly to the right (in the photo)
This meant that the LHS tubes did need to be offset relative to their blast nozzles.

The inner mounting holes of the two LHS tubes were modified to be slots so that  the LHS tubes could be jacked apart from the RHS tubes. In this way, the LHS tubes were made parallel to the RHS ones and held in place after tightening the fixings into the casting.

Once done, both RHS and LHS tube pairs could be seen to be parallel to the vertical cab front joining strap between the RHS and LHS tubes.
Tubes all parallel to the strap between
Instinctively, this was much more satisfactory. The LHS heat shield was fitted first and then the RHS. The tubes inside RHS shield seemed to be rather offset; however, as the spacers and fixings were inserted, the whole assembly seemed to relax into place and fit surprisingly well, much to the relief of both owners.
The complete assembly in place (1)
The complete assembly in place (2)
The two damper flap are still to be fitted but otherwise a major step forward achieved!
View from the inside
View from the outside
For completeness, this is how the assembly looked in 2004:
It's come a long way!

Thursday, 22 January 2015

Making Parallel Chimneys

My previous article on Sentinel 7109's chimneys left a problem to be solved.

One solution suggested was to take off the LHS tubes and grind away the casting to enable the tubes to be realigned. By elongating some of the fixing holes in the tubes, this might have achieved a result. However, I was not happy with the idea of reshaping the castings in this way as it would end up with a vague fit that could come loose when subjected to vibration and heating/cooling during service.

I enquired of one of my mentors (Justin Goold) about how concentric the blast from the blast nozzles needed to be inside the chimney tubes. It would seem that it is important for the blast to be right up the centre of the tubes. Things would work if the nozzles were out of alignment but not very well.

So the first thing to be done is to measure how well the nozzles are aligned at present and hence where any adjustment is needed as it may not be the LHS chimney tubes only. I've had to make an alignment tool to investigate this.

It's important to note that the orifice of each nozzle has a machined area around it which is perpendicular to the direction of the blast. This can be used to work with an alignment tool.
 (The nozzles themselves are a converging cone shape which will not support a rod to check alignment).
Nozzles showing machined flat area around each nozzle orifice
The tool needs to sit in the orifice and follow the line of the blast. I've made it using M10 threaded rod with a foot having a ledge to rest on the orifice surround.
Threaded rod and alignment foot
Alignment foot with ledge to fit into nozzle orifice
The foot has been made carefully and the threaded rod selected so that the latter will accurately follow the line of the blast.

Thus it will be possible to check the alignment of each chimney tube with its own blast nozzle.

The next challenge is to make the chimney tubes all parallel to each other whilst still in line with the nozzle blast. Assuming the nozzles are already well aligned(!), this involves increasing the gap between the LH & RH pairs of tubes at their tops.

I'd noticed previously that when the superheater was tightened down too much, the central part of the boiler top plate was pulled downwards and no longer flat. When I loosened the superheater fixing, it lessened the inward leaning of the chimney tubes slightly although far from enough. However, if the tubes could be made to lean inwards by pulling down the superheater, they could also be made to lean further outwards by lifting the centre of the boiler top plate. Possibly this could be done and avoid grinding the castings.

But how to do it?

What's needed is a device which can push apart the two castings far enough for the heat shields to be fitted (such as a car jack)! With the heat shields fitted, they will keep the chimney tubes in place.

So the plan is:
Check the current alignment of the nozzle for each tube.
If not satisfactory, make minor adjustment (somehow!).
If aligned OK, jack the castings apart until the tubes are parallel.
Reassemble the heat shields.
Remove the jack.

Cross fingers!

Monday, 19 January 2015

Extending the Chimney Bases Upwards

After fitting Sentinel 7109's new chimney bases, Sunday 18th January 2015 was a busy day spent attaching the four chimney tubes.

Having assembled both chimney units completely in my garage before bringing them to site, I was confident that things should go together without mishap. (Odd how it's the one thing you didn't check that comes back to bite you!).

The tubes are numbered from One to Four as Left Front, Left Rear, Right Rear to Right Front. Each tube had been labelled with the corresponding number of Centre Pop 'pips' (really useful if you can find them again!)
Number One Tube in place
Numbers One & Two
Numbers One, Two & Three
Numbers One to Four all in place
All fitted and seeming to be going well.
View from Above
The photo below gives an impression of how the cab will look eventually.
Exhaust Steam Pipe to Numbers Three & Four Tubes
Finally, here's the first heat shield in place and this is where things began to bite back.
First Heat Shield around numbers One & Two Tubes
The one thing I hadn't checked in my garage was how the two chimney pairs looked together. Looking closely at the photo above, the heat shield on the left seems to converge towards the tubes on the right. At first I thought it was a camera lens effect but the truth was revealed when I attempted to fit the second heat shield on the right.

The left and right hand pairs of tubes converged so much that the second shield could not be fitted using the standard mounting method.

After removing the heat shield again, the measured gap between the tubes at their lower end was 5" but only 4.25" at their upper end. Clearly this would not be acceptable (and definitely not a problem that would be encountered on a single engined Sentinel loco!).

In many of the above photos, I've endeavoured to ensure that the vertical strap behind the chimneys holding the two halves of the cab front together is dead upright. As the photos progress, the leaning inwards of the left hand chimney tubes begins to be more obvious.

Now it's going to be a bit of a grind to make the LH tubes upright and parallel to the right hand ones.

Oddly, by rotating tube number two 180 degrees, the leaning is less so it would appear that the part of the tube which fits over the base casting is not quite in line with the tube's axis. However, that is not much help as the mounting holes don't align with it that way round, hmmph!

At one point, I had thought that tightening down the superheater might have distorted the boiler top plate and made the tubes lean inwards. No such luck - life is never that easy!
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