I'm working on a steam motorcycle. I used a Stanley throttle, I would like to use a easier working throttle would a high pressure ball valve work?

The Stanley throttle with the correct throttle linkage leverage on it, works very smoothly on steam up to 450 pounds. With steam pressures at over 600 pounds, the throttle gets impossible to open without bending your throttle linkage. A ball valve works very well. I have seen them used for whistle valves using about 550 pounds pressure. The guys that have used them get about a year or two out of the ball valve before it wires through it's ball valve seats and the valve becomes unusable. Possibly there may be a better ball valve out there that would last longer. The White steamer throttle was designed to work with pressures up to around 1,000 pounds. There recently was a write up in the SACA, Inc bulletin about the White throttle design. The Doble throttle is even more complex than the White throttle, but the Doble's throttle works even better yet.

A quick look at McMaster shows "high-pressure steam bronze ball valve", rated for 250 psi steam at 406°F, max temp of 500°F. It has a carbon/graphite filled PTFE seals. I know these specs are conservative sometimes - would you say there's a good chance that this would survive service as a throttle?

Bill ,
I think a ball valve would be a good cheap choice, with a stainless ball and seat but keep in mind,it is a very non linear valve.
50% open will still allow 64% flow.
I would suggest to build a small CV valve with a taperd seat that will handle the pressure DP .
You might look at a Swageloc- WHitney valve, such as a model 60 Series Ball Valves
Steam Service
(S60P Series)
They have PEEK seats and are rated up to 2200PSI...you will just have to estimate the correct size based upon flow.