Size: 4" steam cylinders, 2½" pumping cylinders with 10" stroke
This pump was manufactured by the Birmingham manufacturer of Tangye. It is numbered 41689 and of size 4x2½x10. It is actually called 'the special pump' and has the minimum of moving parts. It is based on the style of the Cornish Pump.
It runs on steam or air and the valve is actuated by the piston striking a small spring loaded plunger valve at the end of its stroke at each end of the cylinder. This allows steam to enter the valve chamber and push the shuttle valve along opening the main steam port directing mains pressure steam into the cylinder. At the end of its stroke the piston block strikes another plunger valve repeating the same procedure in the opposite direction.