Ball valves

[Kimball McGinley]

Ball valves make a poor throttle because they open too much too quickly. They are really intended for "shut-off" applications. There are some ball valves made that do not have a round hole in them; it is more of a teardrop to try to reduce the too open too fast issue. I studied all this for a work project.

[Fender]

Aren't gate valves also intended for on-off applications?

[Trainman4602]

yes

[Fender]

How about a fast-opening globe valve (i.e. "Whistle valve"). Globe valves are designed for throttling/restricting flow. Everything I've read says that gate valves are not intended for this.

[Trainman4602]

Dan I have been using them for 40 years with great success. The K4 Has one and I have never had trouble with it.

In fact Cagney locomotives have them for throttles.

[Soot n' Cinders]

How about a fast-opening globe valve (i.e. "Whistle valve"). Globe valves are designed for throttling/restricting flow. Everything I've read says that gate valves are not intended for this.

Gate valves aren't intended for throttling, just like ball valves. The flow characteristic curves are nearly identical. Meaning the % total flow to % total opening graphs are alike. Whereas a globe valve is much closer to linear than the curve ball/gate valves have. Not to say they won't work, there's too many locomotives out there with ball valves to say that. They're just not the ideal choice.
I'm going with the globe on my shay. Took a commercial solid bronze glove valve and machined the threads off the stem.
The locomotives in the Stillman-McCormick park in Arizona used this set up for their throttle too, and those are 5" scale 15" gauge.

And another thought, look at a prototype throttle valve. It's essentially a globe valve, and the early T boiler shays actually used globe valves as throttles.

[Fred_V]

My feeling about ball valves is that most of the ones in use are too big thus they open too fast. I had a 3/8" on my 3" bore engine and the opening curve was perfect. I have a 3/8" on the Hunslet 2 1/4" bore and it opens a bit quickly. A 1/4" ball valve would have been perfect and would pass the total flow needed. As it is with the 3/8" the engine will go WAY WAY too fast.

[Pontiacguy1]

It isn't just ball valves. The 4-4-0 that i reworked a couple of years ago had a sliding type valve on it with a round hole. The whole thing looked too big for an Allen loco throttle to me, but I put it back into the new boiler since that is what the locomotive came with. It would open up really quickly too, causing the locomotive to break loose and slip wildly if you didn't open it slowly. It would have been a lot better with a smaller hole in it, I think.

I've found that ball valves are quite controllable when properly sized. Maybe it's just that I've gotten used to them.

[FLSTEAM]

My 2 1/2" Shay 2 x 2 has a 3/8" stainless ball valve that has worked perfect for the last 5 years.

John B.

[Trainman4602]

Yes ball valve that are of quality will work but I don't like the 90 degree open to close.

[BClemens]

How about one of these?

[FLSTEAM]

quoteYes ball valve that are of quality will work but I don't like the 90 degree open to close

My throttle linkage adjusts for that. The throttle has more like 45 deg. throw.

John B.