I didn't realize that there was any history with a tapered plug type throttle. I was obviously wrong.Bill Shields wrote: ↑Tue Jan 01, 2019 10:43 pm I use a tapered plug 'pull' throttle in several of my locos and find them very easy to operate...
You can also consider having a small orifice I the throttle to keep response under control.
My 1-1/2 camelback has a 3/16" hole from the throttle to the 2" diameter cylinders and 9" drivers...the tip of the throttle is a 1/8" nose that clears the orifice after you have the throttle about 1/2 way open.
It is very easy to start and you REALLY HAVE TO TRY to get the wheels to slip....as in whack pull the throttle COMPLETELY OPEN and be on wet rail.
,
You could start with a 1/4" orifice and put a tapered plug with a 3/16" (or so) nose on the end.
The advantage to this type of setup is that you can easily pull the throttle plug out of the back of the boiler and change the dimensions without ripping anything apart to play with dimensions.
I can send pictures / drawings if you like, but it doesn't take a rocket scientist to figure it out.
Of course, I designed everything around this setup...and if you already have a boiler without the back head fitting(s) to allow this, you may not be able to travel this road.
Do I understand correctly that you were feeding a pair of 2" diameter cylinders through a 3/16" diameter hole at full throttle? I must say that sounds awful small. Obviously low speed control must have been very good. BUT, did you experience any speed or load resrictions, particularly any speed restrictions under a heavy load or long hill. My first live steamer project was a Little Engines 0-6-0 with a 2 1/4" bore and 7" drivers. The throttle was a 3/8" NPT ball valve. It was a full port vavle with I'd estimate a 3/8" bore. With that throttle wide open the cylinders would have limited speed/power on a long hill with a heavy load. None the less the tapered plug type of throttle has promise and I think I can squeeze one into my steam dome.
Dave