Sandfields Pumping Station - cataract

Image: © Chris Allen Taken: 28 Feb 2020

This is part of the underfloor workings of the 1873 Cornish beam pumping engine preserved at this site. The device bottom right in a square tank is one of the two cataracts on this engine (the other is discernible behind it). The cataract is a device that adjusts the pause between strokes on a Cornish beam engine. The cam on the shaft above it raises a pump plunger that draws in water from the tank. Gravity then pulls the plunger down at a rate dictated by a valve with an adjustable orifice. As the plunger descends it trips the engine's valve gear to start a stroke. This cataract trips the equilibrium valve to start the outdoor stroke (piston rising in the steam cylinder). The other, disconnected, cataract tripped the exhaust and steam valves (in that order) to commence the indoor stroke (piston descending in the steam cylinder). Various other bits of mechanism are included in the view but are only likely to be of interest to the cognoscenti. Visitors are welcome on a Friday morning but overalls are recommended for those wanting to access the less accessible underfloor locations.

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