Visited Weston Zoyland Pumping Station Museum [near that village, on the Somerset Levels], with a group of fellow-engineering friends.
The Museum had an Open Day with engines in steam, and despite the cold, drizzly weather it attracted a lot of visitors.
Well worth an "Engineers' Day Out", to quote a well-known phrase, and one characteristic I like is that this mid-19C land-draining installation has not been pickled in gloss, as so many of the big professional museums have become. It also has good information boards…. other museums, please note. (Yes, NRM, I do mean you too!)
The central exhibit is its Easton, Amos & Sons pump, a balanced-flow centrifugal unit driven by a twin-cylinder vertical engine above the cylindrical tank holding the pump itself; and in its original position and building.
The engine's slide-valves have the complication of a forerunner to Meyer expansion-gear, with a separate main and cut-off valve each having its eccentric at 90º apart. The latter can be lifted away from the main valve by a lever on the end of the valve-chest – but I do not understand what that achieves. This is a surprising feature for an engine designed to work in one direction only, at more or less constant load so fairly self-governing. Still, it is a modern machine, built in the 1860s to replace the 1831 beam-engine original! I did ask but the volunteer staff admit being as puzzled by this apparently needless complexity as I was.
So, back home, I turned to my copy of Hutton, 1911. He describes with two drawings on p290-291, Expansion-valves; of adjustable, and fixed, cut-off. The former uses screw-adjusters on the valve-spindles. The latter's cut-off is adjusted by altering the eccentric's position on the shaft. Aha! That latter matches so far. This engine's eccentrics clearly have angle-adjustment slots. Now, why? An expansion-valve can give shorter cut-off than with just the lap, where required. Another – I quote:
An expansion-valve prevents expeditious starting or reversing of an engine.
Expeditious starting seems unlikely here, unless perhaps the valve-lifters allow greater safety if an engine in steam in its working days needed unexpected attention. Can a twin-simple engine with ordinary slide-valves driven by plain eccentrics, start in reverse? That seems against all I have learnt about steam-engines, but I defer to Messrs Eaton and Amos; and an engine driving a centrifugal pump must always run in only one direction.
The connecting-rods are linked by parallel-motion rather than crossheads, to the crankshaft whose flywheel I judged about 8ft diameter, is also a bevel-gear whose apple-wood "cogs" (to borrow mill terminology) engage the cast-iron pinion on the top end of the pump shaft. This combination, used in flour-mills to reduce fire risk, gives smooth, very quiet running.
By "balanced flow" I mean the pump has a twin-sided impellor, in the horizontal plane, with inlets above and below. This reduces axial load on the vertical shaft to its own weight, apparently as plain thrust-bearings were still problematical at the time.
Believed the oldest pumping-engine still in working order and original location, the water it pumps is simply circulated as subsequent civil-engineering on the river has raised the levees several feet above the machine's original outlet.
The Museum also has a display of various small plant steam-engines, most in a separate building; and a short narrow-gauge railway giving free rides on open carriages behind a Simplex diesel.
The boiler is not the early-20C Lancashire shown in representative form in the pump-house, but a large Robey portable in a semi-open shed, and fuelled with scrap timber. It cannot supply all the engines at once so the Eaton & Amos takes turns with the others, being run for perhaps quarter of an hour at hourly intervals while the small exhibits rest. The Robey itself is set to run gently and continuously, for its own feed-pump.
£8 standard admission when the engines are in steam, free on non-steam days. The modern tea-shop was selling only hot drinks and cakes but on a cold, drizzly New Years' Day it is a welcome oasis! Tea taking its natural course…. Two up-to-date loos, single-sex and fitted for disability use and with baby-changing shelves.
The modern brother to the pumping-station is alongside, not open to the public, with diesel-driven machines.
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We had every sympathy for one of today's visitors, now having an UN-Happy New Year thanks to reversing a VW Transporter into a branch stump on a heavily-pruned tree next to the car-park. It had badly dented the tail-gate and shattered the window.