41. Six locomotives were equipped with superheating, bore cylinders and inside admission piston valves and were reclassified to Class 8BW. 42. Four locomotives were equipped with superheated boilers, bore cylinders and inside admission piston valves and reclassified to Class 8W. 43. Although they used the same type of boiler they carried a higher pressure and were fitted with piston valves . 44. Seven of the eleven were fitted with larger cylinders, Stephenson valve gear and piston valves , raising the weight to. 45. Early designs used the D slide valve but this has been largely superseded by Piston valve or Poppet valve designs. 46. Pistons and piston valves are made of aluminium and have hollow rods for to keep the weight in desirable limits. 47. The poppet valves were not a great success and they all reverted to piston valve engines between 1931 and 1934. 48. The cylinders were arranged outside the plate frames, with the piston valves above the cylinders and actuated by Walschaerts valve gear. 49. Modern piston valves were developed by Fran�ois P�rinet for the saxhorn family of instruments promoted by Adolphe Sax around the same time. 50. It involves the ceramic coating of automotive parts and components specificallycylinder head fire deck, piston crown or head, and piston valve base.
