< Piston Valve >
The picture shows section of piston valve assembly. The center brown part shows center hole in valve body. Each valve seat consists of 2 of piston rings (2mm) and a guide ring (5mm). The guide rings contact with valve body in I.D. and slide along the steam chest in O.D. Each piston ring has a gap and extends up to the steam chest diameter. Piston rings and guide rings are secured in the valve body by screwed caps. The whole parts have 6mm dia.center holes.
I started with bodies. They are made from gunmetal round bar. Both ends of the bar are turned, drilled and tapped.
With a tailstock support, valve body waist is turned.
It is followed with taper turning.
Note the finished valve bodies have parallel faces for wrenching,
The screwed caps also made from gunmetal round bar. The photo shows cutting parallel faces for wrenching
Piston rings and guide rings are made from 'free-cutting phosphor bronze bar'. A blank for piston rings are turned in O.D.and I.D. Then the rings are parted one after another.
The photo shows jig to grind side faces of the rings.
Ring gaps are cut by a fine sanding disk. Note brass plates sandwich a pair of rings so as to prevent distortion.
Finished piston rings: I designed ring diameter and gap width to leave 0.1mm gap still in the steam chest.
The guide rings are made in the same manner as the piston rings but have no gap.
When assembly, the guide ring thickness is adjusted as that the piston rings spring freely but have no play in axis. In order to avoid slacking, the cap is tightened with Loctite 648 (heat resistant).
Valve spindle is made from free-cutting stainless steel bar. It is 5mm dia. while the valve center hole is 6mm dia. The piston valve is secured by snap rings at both ends. Note the adjusting ring between an e-ring and the valve. The adjusting ring thickness is also adjusted as that the valve moves freely in diameter but has no play in axle.