Friday, 30 August 2013

Order, Order!

As well as restoring Sentinel 7109 ("Joyce"), I've also been discovering her history. Sometimes information comes to light through a deliberate search but occasionally someone turns up a real unexpected gem.

One of these gems was kindly sent to me by John Hutchings from the Industrial Locomotive Society. There are three images which can be magnified for reading by clicking on them (and 'back-arrow' to return). They show the original works orders (7109) for the manufacture of "Joyce".
Page 1
Page 2
Not forgetting the 'sprockets'!
In amongst the information are the figures for the number of gear teeth and sprocket teeth. These allow an interesting calculation of speed per engine RPM.

Crankshaft pinion: 45 teeth.
Countershaft pinion: 102 teeth.

Axle sprockets: 27 teeth.
Countershaft sprockets: 15 teeth.

Engine speed to axle speed ratio:

102/45 x 27/15 = 4.08:1.

Wheel diameter: 36 inches.
Wheel circumference: Pi x 36 = 9.42 ft.

[Feet/mile = 5280].

MPH = (RPM/4.08 x 60) x 9.42/5280 = 13.1 at 500 RPM engine speed.

So we can expect Sentinel 7109 to be speeding along at 13.1 MPH when its engines are at 500 RPM!

Other noteworthy points in the orders show that there was an injector fitted originally and that no Weir boiler feed pump was included; it would appear to have been ordered and fitted later. The boiler was a single 'experimental' type as opposed to some earlier double-engined locos that had used two 100 HP boilers!

I'm also enquiring as to whether similar information is available for the two Radstock Sentinels.

Tuesday, 20 August 2013

Camshaft Surface Finish (2)

In a May 2013 article, I was concerned about how best to remove some corrosion from the surface of one of Sentinel 7109's rear engine camshafts. Holding a file to the surface while turning the engine and camshaft using compressed air seemed a good idea at the time but it became no longer practical after the steam feed pipework had been reconnected.

So I decided, that a strip of emery paper pulled back and forth around the camshaft would have to do.

This is the before picture:
Before abrading
This is the after picture:
After abrading
And with a good slopping of crankcase oil:
Ready to go
Meanwhile, I discovered a strange phenomenon in the front engine's cam-finger chamber.
Strange glow or what?
It took me a while to figure out that the lurid green-ness was the new oil dribbling through from the cam-shift shaft oil chamber into the old oil.

Clearly visible is the word 'STEAM' stamped on the end of the camshaft. This differentiates it from the exhaust camshaft on the other side of the engine. It also looks as if there may be a manufacturing date of some time in April 1946. I had previously not been aware that the camshafts had ever been replaced.

Sunday, 18 August 2013

Engines (2) Cylinders

Before looking into the cylinder tops, a brief digression. I've occasionally been asked about the four 'pips' on top of 7109's engine cowling; some enquirers had assumed these were a peculiar type of chimney where the smoke would rise from.
7109's four 'pips'
However, this is far from the case. In fact they are merely an adjunct to the cylinder covers to allow space for the top-of-cylinder automatic drain cocks. One wonders whether the 'pips' were an after-thought on the designer's part rather than a feature. Oddly enough, later designs did not have them!

Beneath each of the two covers is a pair of engine cylinders.
Rear engine's cylinders showing auto-drain cocks
When a lid is removed, inside it looks like this:...
Front engine RHS cylinder lid
... and inside the cylinder, it looks like this:
Front engine RHS cylinder
The muck is well stuck on and must have been there a long time. I've cleaned out some of it but it's hard to dislodge and will have to stay put.

The cylinder wall looks like this (the others are similar):
Front engine RHS cylinder wall
Some years ago, in my ignorance, I cleaned the cylinder walls with light machine oil. The variation in colour shows where I washed away the brown cylinder oil which probably would have been better left as it was.

On this occasion, however, I drenched the cylinder in new cylinder oil in preparation for running.
Guess who took the photo!
I did the same for all four cylinders, The piston is right at the bottom in the photo below.
Rear engine LHS cylinder
Finally, I got a bit arty and captured the picture below.
It was a fine day!
Then I put the cylinder lids back on as in the second picture from the top. Job done.

The rectangular holes in the cylinder walls are the steam inlet and outlet ports.

Saturday, 17 August 2013

Engines (1) Oil Change

In a previous article, I'd begun to describe the engine oil change (but got distracted on to other oily activities!). Mid-July 2013, I did the oil change on both front and rear engines. The front engine had been topped-up with used (not too clean) crankcase oil (a rather unsuccessful attempt to fling it about by rotating the engine on compressed air. All I'd achieved was to introduce a load of sludge into the works!). The rear engine I'd drained off partly in 2009. I hate to imagine when the last oil change had taken place!
Oil filler 'cap'
Like on most internal combustion engines, there is an oil filler 'cap'. I'd read that each engine needed 10 gallons of crankcase oil so enough had been bought earlier back in 2010 (when I thought it might take less than a year to get 7109 back to life - How wrong I was!).

The crankcase oil is Hallett's Sentinel Crankcase Oil SCC680. It is a viscous oil (ISO 680) and has the specific property of enabling water to separate from it and readily sink to the bottom where there is a drain valve to let it out. This water separation property is important with a Sentinel steam engine which inevitably encounters condensation in the crankcase. (Morris Lubricants also make an equivalent crankcase oil for Sentinels).

Expecting to use 10 gallons per engine, I decided I would log the amount added against the level indicated on the dipstick.

I filled the front engine first with these results:

1 gallon: Not on dipstick.
2 gallons: 1/4 on dipstick.
3 gallons: almost 1/2 on dipstick.

I added a couple of extra litres to make it 1/2 full. (I like to mix imperial and metric units!).

Then the rear engine:

1 gallon: 1/2 on dipstick!

Oddly, I didn't expect this as none had been added since emptying.

So why did the rear engine need 1 gallon and the front 3 gallons to be half full? Simply, I don't know! However, I have to conclude that there must be something that isn't oil also in the rear engine (which was the one without the sludge added!).

Perhaps inadvisedly, I'm not going to investigate this further for now but monitor it very carefully when initial testing begins.

As yet, I also don't know whether is it is best to fill to the top of the dipstick or not. At least there is some spare oil available!

Saturday, 10 August 2013

Safe Safety Valves (1)

Sentinel 7109's new safety valve system is taking shape as shown below.
The Flange and Supporting pipework
I introduced the new pair of Bailey-Birkett type 716SSL safety valves a little while back. I've now obtained the supporting steel pipe fittings and constructed the new support manifold.

Whilst on the surface this construction seems fairly straight forward, it is a safety system and therefore requires rather more formal engineering processes to ensure it is fit for purpose. (It's also my safety I'm concerned about!).

Before I retired, I spent many years on railway signalling and control centre research and development projects. Most were computer based and hence involved formal safety related system/software development project 'V' life cycles. ('V' implies: Define what it has to do; design it; implement it; test the implementation; test it meets the design; test/assess whether it does what it was defined to do originally. And don't forget the traceability!).

Safety valve pipework is somewhat more tangible than software so it would be over the top to do all that but some allusion to the principle is worthwhile.


Firstly, what are the requirements (i.e. WHAT does it have to do)?

The pipework shall:
1. Withstand 275psi.
2. Withstand 230DegC.
3. Support the safety valves.
4. Support the exhaust outlet pipework.
5. Allow the full output of the boiler to pass to the safety valves (4600 lbs/hour).
6. Connect to the original Sentinel boiler flange mounting.
7. Prevent condensation accumulating in the exhaust (i.e. to prevent showering nearby onlookers when the safety valves blow off!).
8. Enable easy removal of the Safety Valves for hydraulic boiler testing.


Requirements 1-8 are ultimately tested or observed; however, they all need to be taken into account during the design process.

Requirements 1 and 2 (275psi & 230DegC) are satisfied by choosing to use mild steel pipe and fittings and avoiding the weaker malleable iron which is not up to the job. It also requires that a flange to connect to the existing Sentinel flange has to conform to BS 10 (1962) Table F or better.

Requirement 3 is satisfied, firstly, by ensuring that there is a vertical 3/4" male BSP thread to connect to each safety valve and, secondly, by using sufficiently heavy gauge material.

Requirement 4 is satisfied again by using the heavy gauge material. Additional support from the cab roof may also be included later to support the exhaust pipework.

Requirement 5 is satisfied by ensuring that there are no parts of the pipework that are of a smaller diameter than the 3/4" inlet to the safety valves.

Requirement 6 is satisfied by using a compatible flange. Easy you would think but when Sentinel made their safety valve mounting, there were no standard flange sizes and ratings! So the nearest standard type needed to be chosen that involved minimal adaptation.

This resulted in a Carbon Steel flange as follows:
A screwed flange of nominal bore 1.5" (to allow a male 1.5" BSP thread to be attached).
A BS10 Table 'F' type capable of 300psi at 232.2DegC.
5.5" Diameter.
Four holes 11/16" diameter on a pcd of 4.125" to fit 5/8" studs.
0.5" thick.

The four mounting holes had to be elongated slightly to fit the Sentinel flange.

The flange dictated that 1.5" pipework had to be used which conveniently led to the considerable strength of the final structure and avoidance of any diameter less than the 3/4" inlet to the safety valves (requirement 5).

Requirement 7 is satisfied by including narrow bore draining pipes in the exhaust pipework.

Requirement 8 is satisfied by incorporating unions into the exhaust pipe elbows so that the pipe can be detached easily. The safety valves can then be unscrewed without having to take the exhaust pipework apart. A cap is screwed onto the 3/4" male thread to seal for hydraulic boiler testing.


Below is an early mock-up I did at South West Engineering Supplies to get the hang of the idea. It was not the first attempt; I started off using 3/4" pipe bends from the 'T' piece to the base of the valves but did not believe it was a strong enough structure to carry the weight.
Early Mock-up
The implementation evolved to the final version by using shorter 'running' nipples having no plain centre section to keep the links as short as possible and by using single piece reducers to convert from 1.5" to 3/4" diameter fittings. Thus I believe I've minimised the number of thread interfaces and maximised the strength of the structure.
The Final Version
The black 'stuff' on the threads is a jointing compound from Rocol called 'Steamseal'. It is more technically called 'Foliac Graphite and Manganese' and is specified to be able to withstand steam pressures up to 2800psi at temperatures up to 600 DegC. Good stuff! Easily exceeding requirements 1 & 2.

At this stage, requirements 1-6 have been embodied into the design and implementation.

Requirement 7's condensate draining pipe is shown below.
Condensate Draining Pipe (bottom left)
To prevent a condensate pool accumulating, the small brass fitting had to be machined so that it would not protrude into the large pipe.
Flush Drainage hole
I hope I've demonstrated how setting out the requirements before design and implementation drives towards a compliant solution. Often, it's easy to assume that what has been done before will do but that approach tends to only just get what you want if you are lucky and doesn't cater for doing something that hasn't been done before.

Of course, if you haven't got ALL the requirements identified at the start, you may still not get what you want!

Next to do is the upward exhaust pipework.

Thursday, 1 August 2013

Oil Out, Rained Off, Oil In

After my last attempt to prevent oil leaking out of the front engine's cam-shift shaft oil chamber, I set out to cure the leak with a gasket of 1.5 mm rubberised cork sheeting.

The offending leak area is shown below in an old photo of the rear engine (which means I probably have a leak on that too!).
Oil Chamber Leak
First a little background: I poked my camera around underneath a Super Sentinel waggon at the 2013 Langport steam rally recently. Sentinel 7109 has very similar engines to the Super Waggon but mounted vertically instead of horizontally beneath the waggon's load platform.

I found the method of moving the camshaft to be quite different on the waggon. Chronologically, the waggon came first so Sentinel 7109's engines are an adaptation of the original approach.

The waggon used the 7109 oil chamber filler location to attach the shaft rotation lever, unlike Sentinel 7109 which has the lever on the end of the shaft.
Waggon shaft rotation technique
This is how it works: (Also on YouTube). Apologies for the background commentary!

Sentinel 7109, instead of having the waggon's rotating sleeve (which did not have to retain oil), has a clamp on sleeve, originally without a gasket.
Clamp on sleeve detached
View to the left...
...and to the right
For my second attempt at sealing the chamber, I painted a 2.75" x 11.75" rubberised cork strip with Heldite and wrapped it around the centre section, secured it in place at the top with gaffer tape and tightened the sleeve over it.

And here's what it looks like:
Attempt No. 2 with rubberised cork gasket
The proof of the pudding is in the filling with oil so that's what I did next but initially with an unexpected surprise.
Not so easy to fill; gasket a bit too effective!
Of course, I hadn't thought that the gasket would also be blocking the filler! Undeterred, I tried the hi-tech solution and jabbed it with a screwdriver.
Hi-tech solution...
...Now holding oil
About half a day later, I took this photo:
No leaks this time (after half a day)
So it looks like I've won this time round!

[Postscript: About a week later there was slight leakage - but not enough to worry about!]

Despite my early difficulties here, Sentinel obviously had faith in the method as they were still using it in post-war locos, the latest I've found it on was built in 1958 (Sentinel 9622).

In 2008, I took this picture of William's engine at Elsecar. (Sentinel 9599 built 1956).
William's Oil Chamber Sleeve
The sleeve is up from and to the right of centre. And guess what? It leaks too (unlike the modified 7109 version, attempt 2)!
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