Model of a Steam Engine Cylinder

Model (scale 1:4) of a Steam Engine Cylinder fitted with McNaught patent 1908 "Drop Piston Valves" on wooden base

This arrangement of steam engine valves, for reducing cylinder clearance to a minimum, was patented by Mr. W. McNaught in 1908. There are four separate piston valves arranged at right angles to the axis of the cylinder and working in perforated liners fitted across the steam and exhaust passages, which are cast along the top and bottom of the cylinder. When the valves are moved outward they uncover the perforations and allow the steam to enter or leave the cylinder. The piston, which is made longer than usual, is allowed to approach as nearly as possible to the cylinder covers, and the valves have conical inner ends which project beyond the cylinder wall and are accommodated by notches formed in the piston and the cylinder covers. Holes are drilled through the valves to balance the steam pressure on their ends. The inlet valves are fitted with dashpots and are arranged to be operated by a trip gear; the exhaust valves may be worked by any ordinary gear.