Another Shay Steam Brake Valve
I was not happy with the valve described in the brake valve section Shay Steam Brake Valve because the passages were too small. The valve worked OK on compressed air but sometimes would not pass steam, especially under lower pressure such as less than 50 psi. I modified the the valve by drilling the passages larger. This fixed the blockage problem but the clearances were reduced with the larger passages and the valve developed a small leak. One solution was to make a new valve designed with larger passages. A valve with 3/32" passages would be satisfactory and this size passage could probably be achieved reliably with a 3/8" valve plug.
I had recently finished building an air compressor/pump that used O-Ring seals and was very happy with the O-Rings. I had also made a blowdown valve using an O-Ring seal and was happy with that design. With these successes I decided to try to make a brake valve using O-Rings. The O-rings will seal against a rotating disk just like the blowdown valve. Recall that the valve must make two connections at once: the steam input to one end of the cylinder and the other end of the cylinder to the exhaust. The passages connecting the between valve inputs and outputs will be within the rotating disk. (This was the view in January 2004).
Update 2/26/2006: I made the O-Ring valve and it worked fine for a few weeks and then started to leak after one of the O-Rings tore on the disk. I replaced the O-Ring and then another tore in a week or so. It turned out this design didn't work very well. After two summers with seldom working brakes I decided to design a new valve using a rotating disk on a thin sheet of Teflon. The disk is spring loaded and the entire valve is pressurized and sealed. This valve uses some of the concepts of a brake valve sold by LocoParts. The LocoParts valve is an excellent value and I recommend it. Unfortunately that valve controls only one end of the brake cylinder and is not applicable to the double ended cylinders used on the early Shays. I deleted the description of the O-Ring based valve from this page and replaced it with the description of the disk-Teflon seal valve which really works.
Photo above shows the finished valve installed on the shelf over the rear cylinder. The cab was off when the photo was taken.