Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

Cylinder drain cocks are always good, I would say yes for your size engine.  I have some "automatics" on a couple of my locomotives, where there is a free floating steel ball in a horizontal chamber. The idea is it will pass water, but the steam will push the ball shut against the seat.  I find the performance marginal, as they get gummed up from steam oil.  You can find plans to make these on line.  I much prefer manually operated valves. This is somewhat difficult on a locomotive as a linkage needs to be run to the rear of the engine, the last one I did was 4 ft. to the back of the engine.  Also used on locomotives are steam operated drain valves, also problematic in small scales.
I buy the manual drain valves specific to locomotive use where the handle is offset to 45 degrees, on ebay. On a stationary engine you could use any configuration of valve.