DRIVING & FIRING
On the footplate of the Talyllyn Railway’s Dolgoch
It is hard to believe that ten years have passed since Steam Railway launched its appeal for Dolgoch’s new boiler, without which the engine would not have been available for the 60th anniversary of preservation on May 14 2011.
To date, the Talyllyn Railway’s famous engine has performed flawlessly. Indeed, in 2012, Dolgoch worked its highest ever distance in preservation, 4,853 miles, spread over more than 160 days.
It is reasonable to ask if such a historic locomotive, built in 1866, should be used so extensively, but retirement from front-line service seems unthinkable. The most important thing is that Dolgoch continues to work the Talyllyn service exactly as it always has.
Dolgoch is a unique engine to drive as, being one of its regular drivers, I well know.
It has been said that the Fletcher, Jennings locomotives are, broadly speaking, colliery winding engines on wheels and that is, or at least was, true. The two Talyllyn engines were unusual for the Lowca Engine Works, built for use on a passenger-carrying railway and not some purely industrial concern. Despite their good looks, numerous brass fittings and high-specification paintwork, these were the industrial shunting engines of their era.
Henry Allason Fletcher designed his narrow gauge engines with terrific power for their size, capable of hauling heavy loads at slow speeds for perhaps half a mile or a mile, by which time steam pressure would likely have run short.
Dolgoch, and its original TR sister engine Talyllyn, feature large diameter cylinders with a very long stroke; an arrangement typical of winding engines. Extremely large valves channel high volumes of steam while the valve gear was arranged to provide cut-offs of 90% and – notched right up – 80%! With no lead [pre-admission of steam at the start of the piston stroke] and virtually no expansive working,
this was brute force steam admission for almost the entire stroke. The engines could efficiently exhaust such large quantities of steam only at around walking pace, or if worked very lightly.
TOP NOTCH
It was by some miracle that in the early 1950s Dolgoch did not suffer a catastrophic failure, mechanical or explosive, following which the responsible ministry might have taken a dim, and potentially gamechanging, view of amateurs running steam.
After both original engines had been rebuilt, Talyllyn in 1958 and Dolgoch in 1963, it was discovered that coal consumption was astronomical with the then longer and heavier trains. Their boilers struggled to keep up with demand, particularly on a non-stop run. It became common practice to bank the two original engines on the lower reaches of the line, to give Talyllyn or Dolgoch a fighting chance of reaching the top without stopping for a blow-up. It was also discovered that these engines could continue to work a train with, amazingly, as little as 25lbs/sq in remaining on the clock! Fortunately, the injectors also worked at very low pressure.
It was owing to the excessive coal consumption that the railway preferred not to use the original locomotives until they had been substantially rebuilt. In Dolgoch’s case, this meant fitting a new axle, bringing the angle of advance on the eccentrics back so that the two forward notches on the reverser gave a cut-off of 45% and 25% instead, much closer to a conventional figure, and effecting a terrific fuel saving.
Because of inherent flaws in the nature of the Fletcher’s Patent Valve Gear, second notch forward is selected as this is the gear in which the engine does 95% of its work. In all other notches, Dolgoch has two strong beats followed by two weaker beats. As such, care must be taken to prevent what old enginemen referred to as ‘boxing’ – setting up an uncomfortable oscillation between the engine and the train. This is exacerbated by the short cut-off, the sprung side buffers instead of a fixed central coupling, and because the balance weights on the wheels are insufficient to compensate for the extremely long outside rods.
An experienced driver will sense the engine and train are reaching their resonant frequency and quickly accelerate through that particular speed, so as to prevent the surging effect from getting worse. With full gear being 45%, there is a 10% chance that there is no valve port opening and so it is not unusual to find Dolgoch has centred and will not go forward, but must be reversed first.
As an 0-4-0 with a wheel in each corner, and on which cylinders overhang the front axle and water tanks overhang the rear, Dolgoch is extremely well balanced and adhesion simply could not be better. There are credible stories of the engine being driven a short way up the incline at Nant Gwernol after the rope had snapped, and when not enough empty wagons were available to meet the rope. The gradient at this point was approximately 1-in-5.
Dolgoch is so sure-footed that the sandbox has not been used since 1953.
One problem caused by the long wheelbase however is that Dolgoch has a tendency to ‘hunt’ when taking a curve too fast. Running down the line, Dolgoch will roll almost the entire distance with ease and will often start away from Abergynolwyn or Brynglas without the need to apply steam. Indeed, the only engine which rolls better is ex-Corris Railway No. 3 Sir Haydn, owing to its larger driving wheels.
OLD LADY
Running backwards with Dolgoch, without the constraint of a rear coupling, an uncomfortable vertical oscillation can be encountered at the back end, normally at around 15mph, the railway’s speed limit. Like its sister Talyllyn, an intimate knowledge of the track is required to obtain a smooth ride.
With an increase in maximum boiler pressure from 80lbs/sq in to 160lbs/sq in, the regulator is extremely sensitive, requiring only the lightest touch to open but a slightly firmer hand to close. In expert hands, Dolgoch works the Talyllyn service effortlessly, with small guiding taps of the regulator, and in her inimitable way the ‘Old Lady’ will respond in her own time and with remarkably little fuss from the chimney.
At the same time however, she remains extremely powerful; the big cylinders with generous ports and large valves remain capable of pulling a train at 40lbs/sq in or less, even if the valve gear no longer permits longer cut-offs.
When the occasion demands, she can really pull, her only equal for maximum permitted load being the railway’s newest engine, No. 7 ‘Tom Rolt’, rebuilt from a 3ft gauge locomotive.
Given a heavy train on a greasy rail, I would take Dolgoch every time, despite the lower weight, not having any sanding gear and the smaller boiler with lower pressure. The normal limit on its pulling power is the skill of the fireman and the driver’s ability to keep the water in the boiler and not prime. With oversized slide valves for the higher boiler pressure however, if either Dolgoch or Talyllyn are opened out, the valve friction becomes enormous putting a significant strain on the valve gear; it is best therefore not to use the power unless absolutely necessary.
Every day with Dolgoch is a great privilege; not only is Dolgoch the engine which started the railway preservation movement, she is one of the world’s oldest regularly working steam locomotives and perhaps the oldest with an unbroken service record, having never been stopped with an uncertain future.
A particular treat is to take her out with the original vintage carriages. Dolgoch with the original Talyllyn train is surely one of the crown jewels of preservation.
Dolgoch is so sure-footed that the sandbox, built into the splasher over the left leading wheel, has not been used since 1953