Friday, 13 January 2012

Driving 'Lion'

'Lion' (minus its tender) being prepared for display in the Museum of Liverpool. The whistle is visible at the top, with its steam cock handle. The regulator handle is at 10 o'clock - the fully open position. The reverser can just be seen on the right of the firebox.

It's over twenty years since 'Lion' steamed but, before that, I had a few opportunities to actually drive 'Lion'. A correspondent asked whether driving 'Lion' was very different from driving 'Modern' locomotives. The answer is "not very". The basic principles of the steam locomotive haven't changed a great deal since the early days but, clearly, all sorts of refinements have been attempted (with varying degrees of success) over the years.

To move a steam locomotive, the driver has to decide which way he wants to move, forwards or backwards, and set the reverser (a lever in 'Lion') accordingly. The driver has to ensure that the hand brake is released (the hand brake will become important when it's time to stop). The driver will then open a steam valve to allow steam to flow from the boiler to the cylinders (there are at least two cylinders, as in 'Lion', but sometimes more) to make it go.

The steam is used to push a piston from end to end of a steam-tight cylinder. The piston is attached to a piston rod which sticks out of one end of the cyclinder and it's the reciprocating motion of the piston rod which extracts useful work. Usually, that reciprocating motion is converted to rotary motion of the driving axle by connecting rods pulling and pushing either a cranked axle (as in 'Lion') or outside cranks (if the cylinders are outside the frames). The driving axle may share its turning torque with one or more other axles via horizontal Coupling Rods. 'Lion' has two coupled axles, coupled via 'Flycranks' mounted outside the outside framing and coupling rods, giving the locomotive an antique, attractive appearance which is quite hypnotic when the engine's moving.

The clever stuff is performed by various bits of moving 'old iron', collectively called the 'Valve Motion' (or 'Valve Gear'), which automatically move a Steam Valve to cut off steam to one end of the cylinder when the piston completes its travel and admit steam to the other end of the cylinder to push the piston back again. Setting the reverser alters the geometry of the Valve Motion to determine which end of the cylinder first receives steam and hence which way the engine moves. There are lots of pictures of 'Lion' and this 'old iron' here.

'Lion' is fitted with an early form of valve motion called 'Gab' which only allows the driver to select direction. Other forms of valve gear (such as the Link Motion) allow the driver to cut off steam earlier in the piston's travel for better efficiency. For instance, the '1400' tank engine shown in 'The Titfield Thunderbolt' has Link Motion controlled not from a reversing lever but from a reversing screw.

The steam whistle gives character to an engine. It's usually sounded before starting as a warning to people in the vicinity but may also be used just to express exuberance. 'Lion' has a single whistle operated by a rotary steam cock. The handle is 'parked' at 6 o'clock - moving it left or right sounds the whistle. I could manage the 'cock-a-doodle-doo' whistle commonly used on railways (called a 'crow') but "On Ikla Moor Baht 'at" requires a two-tone whistle such as provided on Great Western engines (like the '1400' mentioned above).

'Lion' has a lever (or 'pole') reverser standing waist high on the right hand side of the footplate because (in common with most early locomotives) 'Lion' is right hand drive. The Great Western stuck with right hand drive to the very end (the '1400' is right hand drive) but, because railways 'drive on the left' in England, most railways changed to left hand drive to give the driver better visibility of signals which are usually mounted on the left. There's one peculiarity on 'Lion'. Lever reversers normally stand upright when the engine is not moving (this is called 'Mid Gear') and are pushed forwards to go forwards ('Fore Gear') and pulled backwards to go backwards ('Back Gear'). All very intuitive. But, on 'Lion', you pull the reverser back to go forwards and push it forward to go backwards. This was a peculiarity of the partnership who built 'Lion' (Todd, Kitson and Laird) and continued by their successors (Kitson and Company) for a while. Whereas most lever reversers are latched in the selected position by a trigger handle a bit like an old motor car parking brake, LION's reverser has a 'T' handle where the right hand handle hinges to release or apply the latch.

The steam valve that allows the engine move is called the 'Regulator' (sometimes the 'Throttle'). It's a proportionate valve - the more you move it, the more steam flows to the cylinders. The valve itself is within the boiler (where the steam is), operated by rotating the regulator rod. The regulator on most engines (including 'Lion') is operated from a fairly long handle attached to the end of the regulator rod on the footplate to give the driver sufficient leverage to be able to adjust the valve against the pressure of steam inside the boiler. The driver moves this handle in an arc. In 'Lion', it's fully closed at about 2 o'clock and fully open at about 10 o'clock. Different classes of engine have different detailed regulator design and sweep through different arcs. For instance, most Great Western Engines move from 5 o'clock to 1 o'clock. The marvellous Great Eastern '1500' moves from 4 o'clock to 8 o'clock ('underarm'). Left hand drive engines have mirror-image regulator movements. Many L.N.E.R. engines and British Rail Standards have 'Pull-out' regulator handles moving fore-and-aft, where the handle is pulled towards the driver to open it. There's a little more about regulators (including LION'S regulator) here.

Once the train has been accelerated to the desired speed, it's usually possible to partially close the regulator and run under 'easy steam' or fully close the regulator and 'drift'. The regulator is always closed before attempting to brake.

I talk a bit about braking here. In the early days of steam locomotives, effort was concentrated on making machines powerful enough to pull a useful load and braking technology was rather neglected. The 'Lion' has no 'power brake' (usually steam-operated on later designs). There is merely a hand brake operating on the four tender wheels. Since the brake blocks of the period were wooden, this was more of a parking brake - any attempt at 'serious' braking was likely to set fire to the brake blocks!

When I worked on 'Lion' we were giving fairly short demonstration rides so braking wasn't too demanding. Having closed the regulator, we used the traditional technique developed on early railways called 'Counter-pressure braking'. That's the posh term for "shove it into opposite gear and hope it slows down". With steam cut off, selecting opposite gear causes the cylinders to act as air compressors, absorbing energy of motion and slowing the train. We'd usually combine this with judicious use of the tender hand brake to stop in exactly the right place. It's possible to enhance the counter-pressure effect by admitting a little steam - not too much or the wheels will simply spin in the wrong direction and the train will slide.

'Lion' on display at the Museum of Science & Industry in Manchester whilst the new Museum of Liverpool was under construction.

The Museum of Liverpool regard 'Lion' as one of their major exhibits and the locomotive now has pride of place in the Great Port Gallery of the new museum. 'Lion's' starring role in 'The Titfield Thunderbolt' is not forgotten and the Audio-Visual presentations interpreting the locomotive include a number of clips from the film. There's a report on 'Lion' in her new home here.

Since 1984, 'Lion' has her own supporters' club called the Old Locomotive Committee (OLCO) which forms a repository of knowledge about the history of the locomotive. 'Lionsmeet' is an annual meeting of live-steam working models of 'Lion' organised by OLCO. OLCO also has its own website here.

I've written a number of articles about 'Lion' and OLCO which you can find here.

If your interest is broader than just 'Lion', there's also a series of articles describing working on preserved railways and driving various steam locomotives. Most of these articles can be found here.