d. The width of each piston ring must exceed the length of the large exhaust port by at least 1⁄4 inch.
This is to avoid the possibility of piston ring catching in the port.
14. Steam Slide Valves.
a. Slide valves must be machine fitted on all four of the outer edges, the exhaust port edges, and the surfaces in contact with rod connections.
b. The slide valve itself must have its steam and exhaust edges fitted up “line and line” with their respective steam and exhaust ports.
The adding of lap to these edges in lieu of lost motion is not acceptable further than a possible 1⁄32 of an inch to cover inaccuracies of edges.
c. The valves must be guided laterally by guide strips cast in steam chest, and these strips must be machine fitted. The lateral play at these surfaces should not exceed 1⁄16 inch. The height of these guide strips should not be less than 1⁄2 inch, measuring from valve seat.
The construction must be such as to absolutely preclude the possibility of the valve riding up on top of this guide strip.