The On-Line Magazine of Rideable Model Railroading
© October 31, 2012
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The "Gumz" Turret Valve Part 1
Written by Charles Reiter
The Gumz Turret Valve takes its name from its designer Dave Gumz. Dave was a life member of the Golden Gate Live Steamers and is one of the "good guys". One of those fellows that was always ready to help if ask but would not interfere by venturing the un-requested opinion. Dave was a meticulous builder whose career in scientific systems made him a very precise designer and machinist.
When Dave started building his first locomotive, a narrow gauge Mason 2-6-6, he need a turret valve. Working in the science discipline he was familiar with Hoke Teflon sealed valves and used a simplified version of the in a turret array. That 4 valve array was installed in 1981 and has not required any maintenance in the 6000 miles he put on the locomotive. He has retired from “hernia gauge” but is still ready to help with his great experience in steam engineering.
The design is very straight forward and can be made with normal shop tooling. Everyone’s shop has different capability so my method may not be right for you but by following the steps and careful work you will assure your success. I made enough parts for 4 valve clusters at the same time so I tried to optimize batch work. But my description is mostly focused doing all the operations on one part at a time rather than groups of parts.
The heart of the design is the valve body. I chose to make these of threaded brass rod, 3/8-24, rather than thread the 3/8 section. I cut blanks 1.25” long. Leave enough extra for cleanup if your cuts are rough or out of square. I recently added a precise miniature cutoff saw to my shop so that blanks can be cut to size with a finished surface and very little waste. This is a great method if you have enough work to justify the expense. I have a collet lathe, and for making fittings nothing is better but, you can get great performance out of a 3 jaw chuck by using a threaded split bushing. This is a straight bushing threaded and then split with a fine saw down the side so that it tightens when clamped in the chuck or in a collet. I used one for making the valve stems. Holding in 3 jaw chuck without a bushing has the liability of damaging the threads due to the higher pressure of the jaws line contact.
So now that you have a valve body in the lathe, turn it down to .248” for a length of .875”. The under 1/4” size is so that there will be room for the braze material in the manifold assembly. Then turn the blank around and turn down the other end to .312” for .125”length. Now on the same end center drill with a 1/4 inch diameter center drill until the diameter is just starting to raise an edge. This is to support the next operation. Grind a 1/4” drill for a flat bottom and be sure to dub the cutting edges to keep it from hogging in. Use this special drill to make a square bottom recess to a depth of .125”. Next use a #21 drill and drill .75” deep measured from the front surface. This is where the 10-32 threads go, but before threading drill the rest of the way through with a #36 drill. Then thread 10-32 down about .625”.
Now the valve seat is made by drilling to a depth of .813” from the front surface, with another modified drill bit. The drill is a #21 but the end is ground to make a flat bottom. It should just remove enough to create the flat surface or more importantly the square edge at the # 36 passageway we drilled earlier. You don’t want to go to deep and being a little shallower could be useful if you need to clean up a seat in the future. I put a sleeve over the drill so I could drill to the same depth reliably. This completes the valve body, excluding deburring. The front recess should have smooth surfaces at the edges and the remaining 38-24 threads should be clean with the start point softened. The 1/4” ends of the valve bodies are intended to get threaded or connected with compression fittings, and if you have it all figured out it may be easier to thread them in advance.
The valve seal is a piece of 1/4” Teflon rod 1/8” long with a 1/8” hole drilled through the center. Teflon is soft and deforms easily, so I drilled to a depth of only about 1” length at a time. I was concerned about the drill drifting off center in unsupported material. Then I used my little saw to cut the 1/8” pieces. The valve manifold is a 1/2 square brass rod that I chose to turn to round between the areas that hold the valve bodies. It can be left square as Dave did on the first one or even could be made of round stock. The square is easier to fixture. I made both 4 & 5 valve units and the layout for those is provided on the drawing. For turning the round areas I mounted the part in a collet, and supported the free end on a live center. I just turned to lines drawn on the part. The 4 valve unit was made to go vertically and was threaded 1/8 npt on the top. The 5 valve unit was fit to an existing 4 bolt flange. The unused ends are threaded 5/16-27 for a plug or additional valve position. The holes for the valve bodies are .25” and the passageway over the length was drilled .187”, so it would give a nice clean hole at the finish. Once the valve bodies are brazed in the part becomes difficult to clamp so the final cross hole was drilled 1/4” with a hand drill, the part being set it in a bench vise.
Once the bodies and manifold are done they can be brazed. The fit should be a good sliding fit so the braze material can get through. After fluxing everything I set the valve bodies in the manifold leaving them slightly away from the front surface so I could get a little braze material in there if there was any problem but the material ran through and the bodies would suck up to the surface. I used a 1/32” silver solder wire which makes it easier to control. Keep the heat on the big part and probably using propane is a good approach. I had sandblasted the manifold to see what it would look like but I taped everything and sand blasting it again to clean everything up after it was done. It gives it a nice almost casting look. Valve stems are made of stainless steel threaded rod. Mine were made of salvaged 10-32 bolts. 8-18, the generic stainless for screws, is a good grade of stainless for machining.You of course could use brass or threaded bronze rod if you like.
I used a threaded bushing to protect the threads mounting that in a collet. I cut the shaft size to 1/8 for .625” long. I decided this was a good time to drill and tap for the bolt that retains the handle. If I should break off a tap then I would not have a lot invested in the part yet. Maybe drilling and threading should be the first step. I then turned the valve stem around and cut the unthreaded section at .156 at leaving a .25 long threaded section. Next the 60 degree angle on the end. I got away with using an angled cutter rather than using the compound. I held it by the threaded portion in the bushing to keep it as stiff as possible.
Continued in Part 2
Written by Charles Reiter
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The On-Line Magazine of Ridable Model Railroading