Hi All
Cylinder drains are operated via the 'ALT' + 'D' key command, however at this time it only turns particle effects on/off, it does not effect performance.
Not all locomotives take advantage of this, however, some either don't have any at all, or have automatic effects, or have them on all the time. The alt+d command was added in Trainz Classics 3, so any locos created for earlier versions will not use this. Most (if not all) of the Settle and Carlisle pack's locomotives use the ALT+D function, since they were originally designed for Trainz Classics 3.
For any content creators who may see this, to take advantage of this function, the attachment points for the cylinder drain effects need to be named 'a.drain#' (where '#' is the number of the attachment point, e.g. a.drain0, a.drain1, etc). You can have quite a few drain effects (see my F class 2-4-2T, under the username 'S301', which has at least 8 cylinder drain effects, which are also timed to the wheel animation).
Regards