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| The queen definitely looks younger in this photo! |
Saturday, 8 October 2011
Many thanks ...
... to all who kindly made donations to the Sentinel 7109 restoration project at the S&DRHT AGM on Saturday 8th October 2011. Much appreciated!
Thursday, 6 October 2011
Boiler Lagged and Cladded
Nigel Dickinson, Mike Colborne and myself spent Wednesday 5th October 2011 at Mendip Steam Restorations' workshop affixing Sentinel 7109's boiler lagging and outer cladding sheets. Previous articles (1, 2) have shown the preparation of the 'duvet' and outer cladding sheets ready for this day.
First of all, the boiler had to be brought inside from where it had lain for some months.
Once set up inside, the two happy-chappies got to work with the lower 'duvet'...
... followed by the upper 'duvet'.
The apertures in the finished 'duvet', thankfully, really did fit over the fittings as planned.
Then the cladding sheets needed to be fitted and pop-riveted together to hold them in place. The sheets also had to be riveted to a lower ring support on the boiler and an upper ring above. Whilst the 'duvet' had gone on easily, this was a more onerous task requiring the sheets to be attached and then squeezed over the 'duvet'.
Things got rather busy and strained in this process so the photographer had to take time out to do some real work!
So we got it done in a day! I have to admit to going home feeling rather smug and relieved that it was ready to install after really quite a long time in preparation.
A date is now set for the boiler to be craned into 7109 and it's soon (but secret!).
Spending a day in Mendip Steam Restorations' workshop was an experience in itself. This is a place where real heavy-duty work takes place; I was immensely impressed at the scale of the activities and how things progressed quickly compared to the months we have taken on 7109's activities.
Here's a few photos to illustrate.
This is probably the biggest lathe I've seen. I don't know what the component was but it was about 5 feet in diameter.
Many thanks to MSR for all the help and advice over the months - keep up the good work!
First of all, the boiler had to be brought inside from where it had lain for some months.
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| Tight manoeuvres in the yard... |
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| ...and a squeeze past obstacles in the doorway |
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| Nigel and Mike clearly enjoying their work! |
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| Self-adhesive Aluminium tape fills the gaps... |
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| ... to hold it all together |
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| Snug fit |
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| Upper ring holes being drilled-out ready to take the rivets |
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| Nigel clearly considering how to drill his left thumb joint! |
So we got it done in a day! I have to admit to going home feeling rather smug and relieved that it was ready to install after really quite a long time in preparation.
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| The finished, painted article ready for installation in 7109 |
Spending a day in Mendip Steam Restorations' workshop was an experience in itself. This is a place where real heavy-duty work takes place; I was immensely impressed at the scale of the activities and how things progressed quickly compared to the months we have taken on 7109's activities.
Here's a few photos to illustrate.
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| Andy Melrose clearly ready to attack the boiler to the right! (Note the 100HP Sentinel fireboxes in the background) |
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| Fitting the boiler front section with its owner close to hand |
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| Richard Philips (not posing) whilst doing a 'little' turning (he was actually shoeing the pet dog away!) |
Large-scale turning in action (also on YouTube)
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| Traction-engine boiler currently under construction (1) |
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| Traction-engine boiler currently under construction (2) |
Tuesday, 4 October 2011
Chuff-Synchronisation - Now what's that all about?
Richard Nixon, drawings' custodian of the Sentinel Drivers' Club and Isebrook's carer, emailed me recently with a technical query about double-engined Sentinels.
His concern was that, with two engines, if they were not coupled together so that each chuffed up their respective chimneys at the same time, instead of air being drawn up through the fire, would each engine merely suck air back down the other engine's chimney?
To understand the point, a bit more needs to be known about how a double engined loco works. In particular, each engine has its own double chimney mounted immediately above the firebox.
Blasting exhaust steam through a nozzle in each chimney tube draws air upwards through the chimney. The air should be drawn up from below through the firegrate.
This all works fine if both engines chuff at the same time; however, if they don't then air can be drawn down the un-chuffed chimney instead of up through the fire (probably being the path of least resistance). The result would be a poorer fire in times of need.
So are 7109's two engines chuff-synchronised?
I had originally thought this was true and that the two engines on 7109 were gear locked together.
From the above picture, it looks as if there would be a gear for each engine in its upper gear case (black, like a pair of eyebrows) meshed with the larger gear in the rusty/grey gear case below. (There is the same situation on the other side). If all these gears were in place as described, then the two engines could have been chuff-synchronised together.
However; to my surprise, when I first undid the oil filler cap in the front engine's off side gear case (the one to the right in the photo), I found that the gear case was empty. On the near side, the rear engine's case was also empty.
At first, I thought we'd been diddled but then it dawned on me. There is a sprocket for a chain to drive the front axle from each lower gear; the two gears are not linked and rotate on a fixed, 'dead' axle. Thus the engines rely on the chains being set appropriately and tightly enough to achieve chuff-synchronisation.
It's doubtful that chuff-synchronisation was achieved particularly well in both directions due to slack in the chains.
This situation evolved in later double geared locos such as Sentinel 9622.
9622's chains are double width, presumably for extra strength. These were most likely adopted because of the double gearing. Depending on whether low or high gear is selected, the drive will be transferred to the front axle by one chain or the other but not both. Hence all the driving force has to go via a single chain in contrast to 7109 where both are used at the same time.
To make the double gearing work, both engines are locked together at the end of the crankshaft where the gear is engaged. This happens by having a gear in each upper casing meshed with the gear in the lower casing.
However, there is still more to the picture: double geared engines have a neutral setting in which neither high nor low gear is engaged and the engines can be run with neither load nor locking together. This enables better warming through of the cylinders prior to loco movement.
Of course, the asynchronous rotation of the two engines in neutral means that when they are put into gear, they could be in any relative state of rotation. As such, sometimes they might be chuff synchronised and sometimes not in an unpredictable manner.
So Sentinel 7109, 9622 and other double engined locos have the same problem.
There is yet another consideration and that is to do with the resonant frequency of the chimney system. This may not be relevant if the chuffing frequency never gets high enough to reach resonance and I am sticking my neck out here due to lack of in-depth knowledge of this type of system. (Ask a designer of resonant, high-performance, car exhaust systems!).
Below resonance, a chuff up one pair of chimneys could easily pull air down the other pair if out of sync. At resonance, I do not know what happens. Above resonance, the chuffing will be so fast that sucking air back in won't take place and each chimney will behave as if sealed. (I'm assuming that the chimney system behaves like a ported loudspeaker enclosure).
So the conclusion to all this? I think we'd better just try it and hope for the best!
His concern was that, with two engines, if they were not coupled together so that each chuffed up their respective chimneys at the same time, instead of air being drawn up through the fire, would each engine merely suck air back down the other engine's chimney?
To understand the point, a bit more needs to be known about how a double engined loco works. In particular, each engine has its own double chimney mounted immediately above the firebox.
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| Twin double chimneys |
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| Plan view of boiler showing the twin double chimneys |
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| Single exhaust pipe divides to feed two chimneys |
This all works fine if both engines chuff at the same time; however, if they don't then air can be drawn down the un-chuffed chimney instead of up through the fire (probably being the path of least resistance). The result would be a poorer fire in times of need.
So are 7109's two engines chuff-synchronised?
I had originally thought this was true and that the two engines on 7109 were gear locked together.
 |
| A gear case on the end of each engine crankshaft with the larger gear case below |
However; to my surprise, when I first undid the oil filler cap in the front engine's off side gear case (the one to the right in the photo), I found that the gear case was empty. On the near side, the rear engine's case was also empty.
At first, I thought we'd been diddled but then it dawned on me. There is a sprocket for a chain to drive the front axle from each lower gear; the two gears are not linked and rotate on a fixed, 'dead' axle. Thus the engines rely on the chains being set appropriately and tightly enough to achieve chuff-synchronisation.
 |
| Twin sprockets for chain drive to front axle |
This situation evolved in later double geared locos such as Sentinel 9622.
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| Sentinel 9622's drive chains |
To make the double gearing work, both engines are locked together at the end of the crankshaft where the gear is engaged. This happens by having a gear in each upper casing meshed with the gear in the lower casing.
However, there is still more to the picture: double geared engines have a neutral setting in which neither high nor low gear is engaged and the engines can be run with neither load nor locking together. This enables better warming through of the cylinders prior to loco movement.
 |
| Front view showing different sized gears at each side (Diagram derived from 1930 A2 drawing, courtesy Richard Nixon) |
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| Side view of upper and lower gear casings (Diagram derived from 1930 A2 drawing, courtesy Richard Nixon) |
So Sentinel 7109, 9622 and other double engined locos have the same problem.
There is yet another consideration and that is to do with the resonant frequency of the chimney system. This may not be relevant if the chuffing frequency never gets high enough to reach resonance and I am sticking my neck out here due to lack of in-depth knowledge of this type of system. (Ask a designer of resonant, high-performance, car exhaust systems!).
Below resonance, a chuff up one pair of chimneys could easily pull air down the other pair if out of sync. At resonance, I do not know what happens. Above resonance, the chuffing will be so fast that sucking air back in won't take place and each chimney will behave as if sealed. (I'm assuming that the chimney system behaves like a ported loudspeaker enclosure).
So the conclusion to all this? I think we'd better just try it and hope for the best!
Friday, 30 September 2011
Appeal for 'JOYCE' & her maker's plates
Amongst the Sentinel 7109 missing items are the 'JOYCE' nameplates and the Sentinel maker's plates specific to works number 7109. These were mounted on the side of the cab as in the photo below. I have no idea where these plates are but the chances are that since the loco survived, so did these plates; but where are they now?
Sentinel Waggon Works had various designs of maker's plates and the design specific to 7109 is shown below. With a lot of work, a new pair could be recreated from the design; however, I don't have those sorts of skills, nor the time with all the other restoration activities in progress.
Another simpler approach is to make a mould from another actual plate such as the one below. The drawback is that the result always comes out slightly on the small side due to shrinkage of the cast metal when it cools. (Normally a pattern is made oversize to suit the shrinkage of the particular metal to be used).
Peter Mitchell, owner of Isebrook (6515) at Quainton Road, has kindly offered to make one available should we decide to do it this way. Obviously, we would have to blank out the 6515 and replace it with 7109.
But I'm still wondering where the originals are. I'd be really glad to hear from anyone who can throw some light on their whereabouts. Please post a comment below if you can help.
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| Sentinel 7109 Near-side 'JOYCE' & Maker's Plate |
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| Locomotive Maker's Plate Design |
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| Isebrook's (6515) Makers Plate |
But I'm still wondering where the originals are. I'd be really glad to hear from anyone who can throw some light on their whereabouts. Please post a comment below if you can help.
Tuesday, 27 September 2011
Sentinel 7109's Lower Gear Housings
Since July 2011 (now September), I've taken some better photos for this article so here's the new 'enhanced' version!
Three new inspection bolts have been made for the level check holes in the lower gear housings.
So why three level check holes and not just one? Simply, it depends on the size of the gear wheel inside. Sentinel offered the ability to change the gear ratio to suit each customer's haulage and speed requirements.
7109 was set up for slow, heavy haulage (I'm guessing here but it will be obvious in due course); hence it will have a large gear in the lower gear case. As a result, it will not need such a deep oil bath as one set up for higher speed with a smaller gear in the same place. So the the check hole actually used will be to suit the expected oil level inside.
Going off-subject for a moment, the Teifi Valley Railway visit on 18th September 2011 revealed an interesting angle on this with the double geared Sentinel 9622 built in 1958. Have a look at the next two photos:
Note that the drain cock (posh way of doing it) on the near side is on the middle level whereas, on the off side, the drain cock is on the top level. At first, this seems to be a mistake; however, it is a double geared loco with different sized gears in the near and off side casings. Hence a different oil level is needed for each. (It's inevitable that however many photos are taken at the time, something else needs to be illustrated when the time comes. Anyway, hopefully these are just about good enough to illustrate the point).
Also noteworthy in the 9622 photos is that bolts rather than studs/nuts are used to fix the plate in place.
Does anybody know what that big nut-like thing is in the middle of each cover plate? I guess it's a means of draining condensate from the gear case but it was so covered in green slime and it was raining hard that day so I didn't feel much like crawling about underneath and cleaning it up to find out!
A final noteworthy point: in the bottom right of the off side photo can be seen a drive chain. 9622 has double width chains whereas 7109 has single. The double chains would have been used for extra strength as, with double gearing, the drive would be only via the left or right hand chain depending on whether high or low gear was selected. 7109 has one single width chain per engine.
Back to 7109: the new gear housing bottom plates are under construction in preparation for crankcase oil to be added. Hopefully the oil will dampen the unceremonious 'clanking' heard when running on compressed air without a load.
Crankcase oil is a special type designed for Sentinel steam engines. Its specific characteristic is that water condensate separates out and sinks to the bottom easily for draining off.
When fitting 7109's gear case bottom plates, a gasket will be required between the plate and the housing. Hexagonal headed screws will need to be used with fibre washers to hold it in place as some of the holes into the housing are open to the oil contained within; without fibre washers and fixed-head screws, the oil will be able to seep out via the thread in the housing and the thread in the nut and possibly also between the nut and the bottom plate.
Three new inspection bolts have been made for the level check holes in the lower gear housings.
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| Inspection bolt with blind axial hole and linked radial aperture for oil level checking |
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| The bolt is partly removed to check if oil comes out of the radial aperture |
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| View from above |
7109 was set up for slow, heavy haulage (I'm guessing here but it will be obvious in due course); hence it will have a large gear in the lower gear case. As a result, it will not need such a deep oil bath as one set up for higher speed with a smaller gear in the same place. So the the check hole actually used will be to suit the expected oil level inside.
Going off-subject for a moment, the Teifi Valley Railway visit on 18th September 2011 revealed an interesting angle on this with the double geared Sentinel 9622 built in 1958. Have a look at the next two photos:
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| Near side lower gear casing (9622) |
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| Off side lower gear casing (9622) |
Also noteworthy in the 9622 photos is that bolts rather than studs/nuts are used to fix the plate in place.
Does anybody know what that big nut-like thing is in the middle of each cover plate? I guess it's a means of draining condensate from the gear case but it was so covered in green slime and it was raining hard that day so I didn't feel much like crawling about underneath and cleaning it up to find out!
A final noteworthy point: in the bottom right of the off side photo can be seen a drive chain. 9622 has double width chains whereas 7109 has single. The double chains would have been used for extra strength as, with double gearing, the drive would be only via the left or right hand chain depending on whether high or low gear was selected. 7109 has one single width chain per engine.
Back to 7109: the new gear housing bottom plates are under construction in preparation for crankcase oil to be added. Hopefully the oil will dampen the unceremonious 'clanking' heard when running on compressed air without a load.
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| The bottom plate goes here |
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| Definitely Crankcase oil required! |
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