< Piston Valves >
The picture shows section of my piston-valve cylinder. I designed it as simple as possible so as to make the construction easier than the original slide-valve cylinder.
1) The valve has no piston ring.
2) The steam chest liner is not press-fitted but close-fitted with a sealant.
3) The valve is made from ground rod.
4) The valve bore is finished with a parallel reamer.
The steam-chest liners are made from gunmetal rod.
It is turned down to a close fit in the steam-chest bore, and drilled slightly smaller than the final inner diameter.
Grooves for steam-port are turned with a parting tool.
The groove-to-groove distance is controlled by lead screw of the lathe.
The upper and lower slots are cut with a metal saw.
Width of the slots should be exactly the same as the grooves.
The steam inlet and outlets are cut in the same position as those of the cylinder block.
With a boring tool, the bore is opened out to a shade undersize, and finally finished with a parallel-reamer.
The piston valves are made of ground stainless steel bar.
The center part is reduced with parting-tool and roundnose-tool, while the both ends are left as the ground diameter.
The valve is reversed and finished to a final length in a home-made brass corret.
The bore is drilled slightly oversize of the valve spindle.
The valve will be fixed onto the spindle with E-rings.
The position of grooves for E-rings are determined from actual job.
Finished liners and valves.
The liner is fit to the cylinder-block with Loctite 510 (anaerobic sealant with heat resistance) and secured with screws.
The sealant is immediately cured in the absence of air, so the assembly should be completed within a second. Overflow sealant in each port is removed with cotton swab.
I did a steam test for the cylinders with Aster's gauge 1 locomotive.
I boosted the power of this little engine with an electric blower on her chimney. Once the cylinder was warmed up and dried, the piston moved smoothly according to the position of the valve.
The side covers for the cylinder block are made from brass sheet. The sheet is bent to "U" shape and divided in two covers. A pair of round bar and angle is useful for such a bending work.