207 – Chasewater Railway Museum Bits & Pieces From Chasewater News – Autumn 1997– Part 3 The Sentinel

207 – Chasewater Railway Museum Bits & Pieces

From Chasewater News – Autumn 1997– Part 3 The Sentinel

Sentinel early BR colours

SENTINEL

 Sentinel was built in 1957 by Sentinel of Shrewsbury with the works number of 9632. It was bought by the West Midlands Gas Board for use at Pleck Gas Works, Walsall and was the last steam loco of the upright boiler design built by the Sentinel Company.  Upon arrival at Chasewater the 4wVBT was assigned the number 5 and has been in regular operation ever since.

Early Sentinel shot

Sentinel 9632 at Chasewater

Nigel Canning

The concept of the Sentinel shunting loc was nominally quite clever in that it allowed a loco of relatively low horsepower and size to produce a useful tractive effort and shunt relatively heavy trains, albeit at the expense of a reduced maximum speed.  This is, of course, also true for industrial diesel shunters where shunting speeds much above 10 or 15 mph are unnecessary as well as undesirable from the safety point of view.  Problems arise, however, when you try to reverse the role and run light trains at relatively high speeds as we do at Chasewater.  It is not difficult to imagine a rail-connected industrial concern a few years ago owning a Sentinel and a Hawthorn Leslie similar to ‘Asbestos’ and using both locos to do similar work.  However, if opened up, ‘Asbestos’ can produce several hundred horsepower and a maximum speed far in excess of its road holding capacity.  Consequently, on the causeway bank, ‘Asbestos’ will out-perform either of the diesels or the Sentinel, which is always likely to struggle due to its relatively low power to train weight ratio and low maximum speed, which prevents a decent run being taken at the bank.

When 9632 arrived at Chasewater in 1982 we set about getting it into good working order.  The big worry then was whether or not it would be capable of operating passenger trains reliably.  Eventually we proved that it was, although at that time it was only a matter of moving a single coach back and forth between Brownhills West and the bridge at Willow Vale.

Over the years various modifications were carried out to try and improve the performance of this ‘one man operated’ shunter attempting to run passenger trains.  This culminated in the reliable running of two coach trains to a point about half-way between Willow Vale and the bottom of the causeway bank.

WD SentinelWhen the loco came out of service at the end of 1995 for its major boiler examination, it was decided to further improve running performance.  These are a few of the modifications carried out to achieve that.  One of the main problems has always been the very limited boiler capacity.  Timing the boiler being filled from the loco shed hose pipe shows that there is less than 10 gallons difference between ‘bottom’ and ‘top’ of the gauge glass.  Combine this with the fact that on shutting the regulator when the engine is working hard the level drops by half a glass, or when the safety valves pop you lose half a glass, and a notice in the cab warning ‘IMPORTANT: Water level should never be higher than half glass’ things are never going to be easy.  Originally the loco had the controls for the injector and the Weir pump on the driver’s side, leaving the fireman with nothing to do but shovel coal occasionally, and the driver with the headache of maintaining boiler level in addition to driving.  Both of these controls have now been re-positioned on the fireman’s side, and the Weir pump itself turned sideways to make a bit more room in the cab and give better access for draining it in the winter.  The lubricator sight glass tube has been filled with anti-freeze mix rather than just water so it can survive the winter without attention.  The Weir pump itself is always very messy with excess oil, probably because it always gets a double dose, on from the engine lubricator and again from its own lubricator.  This may have to be rectified at a later date, but in the meantime at least it won’t go rusty!

For a long time the pump has been blowing live steam through to exhaust due to bad corrosion of the valve spool.  This is a weird |Weir arrangement, which looks like a cross between a slide valve and a piston valve enabling the piston to move up and down without any rotating parts being required.

The cast iron spool had to be built up with weld, the intricate pattern of ports ground and filed back to shape, and then the complete spool ground back to the correct diameter.  The result is still not perfect but the pump is now a lot quieter in operation and starts more reliably.

The loco was designed to use superheated steam for the blower, but because the engine lubricator feeds oil 9in immediately after the superheater, all superheated steam has oil in it, which promptly burned to form carbon, blocking the blower jets every few months.  This has now been re-piped to use saturated steam, and new stainless steel blower rings have been fitted with finer jets making the blower more effective on low pressure during lighting up.  The control valve has also been moved to the fireman’s side of the cab.

Boiler outer shell

The vacuum brake system, which was fitted at Chasewater, has gradually evolved over the years, the latest mod being to supply the ejector with superheat steam.  Previously, when using saturated steam from the top of the boiler, any rough bit of track combined with slightly high water level could spill water into the system temporarily destroying release pipe vacuum and partially applying the brake.  Using superheat steam avoids this problem but may possibly erode the pipework or ejector nozzle over a period of time, as well as rob the engine of some of its lubrication.

A new superheater coil was fitted in 1982 and worked without problem for the first five years, but later, small bits of rust about the size of coffee granules started to be thrown up out of the superheater, jamming the regulator open and damaging its seating faces.  To cure this, a perforated stainless steel baffle has been made and fitted in the regulator housing so that any debris now piles up behind it and can be cleaned out occasionally when convenient.

During the recent boiler examination one of the boiler tubes was found to be leaking through a pinhole during the hydraulic test.  This meant that the boiler, which had just been re-assembled, had to be split again and a new set of plain tubes fitted.  At least the tubes are relatively short, and there are only fourteen of them, so they are cheap to buy and will fit in the boot of a car.  The extra work was completed in a couple of weekends and the boiler subsequently passed its hydraulic and steam tests.

When, in 1996, the loco was eventually tried out on a passenger train to Norton Lakeside the result was fairly disastrous.  With two DMU power cars making a trailing load of around 75 tons, 9632 struggled to move at all, let alone climb the causeway bank.  Upon eventually reaching Norton it was found that the loco would hardly make steam even when standing due to the poor coal.  The round trip took an hour and a half, forcing the decision on whether to change the coal merchant, or fit a corridor bunker to allow crew changing at the half-way point on the journey!  The coal was subsequently returned to the supplier!

Two further trips were made on that day, but the third ended in total disaster.  One of the tappet adjusters had worked loose and out of adjustment causing the engine to run on one and a half cylinders, making it snatch a bit.  On the climb back up to Brownhills West one side of the duplex drive chain from the engine to the front axle broke, the loose bit climbed over the sprocket, jammed, and almost ripped one of the gearboxes out of the frames, shearing its mounting lug with a loud bang.  The loco was a total failure and had to be removed to the shed where it remained for the rest of the year whilst repairs were effected.  This involved building up the damaged sprocket teeth with weld and filing back to the correct profile, purchasing an 18 inch length of new chain and modifying it to fit, and drilling and grinding away the back of the front buffer beam so that a new gearbox mounting lug could be fitted in its place.

Sentinel at Pleck Gas Works Nearly newSentinel at Pleck Gas Works, Walsall – nearly new.

In 1997 the loco again passed its boiler test and was subsequently tried out on trains.  The first test was to shunt around 180 tons of assorted wagons and dead engines up out of the shed road, which it did fairly effortlessly and without the chain breaking.  Next it piloted an ailing DL7 and a single coach on a couple of passenger trains to Norton and back, then spent the rest of the day working trains on its own.  Since then it has successfully run two-coach trains to the normal 45 minute schedule and appears to be quite happy, although speed at the top of the causeway bank is little more than a fast walk.

As expected, the main problem is control of the boiler.  With a good hot fire it is quite capable of producing more steam than the cylinders can cope with, but if you have to stop unexpectedly, as is the case when the local toe-rags have been bust piling things up on the line, all hell lets loose from the safety valves within seconds of shutting the regulator.  Even during planned stops this can be a problem as both our stations are approached up steepish banks requiring near full pressure right up to the last minute.  The surprising thing is that the latest batch of coal, which produces enormous amounts of clinker, blocking the grate to the extent that the fire looks completely black from underneath, still produces enough heat to run trains all day without any fire cleaning.  At the end of the day hardly any ash has made it into the ashpan, and when the grate is dropped the fire remains in position without visible means of support until it is hacked out with the fire iron.

On diesel days the loco is being gradually repainted in gasworks red livery, but as this involves a couple of hours each time just to clean and de-grease it after the previous steaming, progress is slow.  A number of modifications and repairs are still planned, but now the loco is back in regular service it is likely to be some while before they are carried out.

Sentinel

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