< Whistles 2 >
The whistle valve is typical ball type. For delicate pressure control, I make the valve stroke reasonably long. As a result, there was no space for coil spring in the valve body. Therefore I added a round chamber for spring at the opposite side of the steam turret. Incidentally diameter of the valve chamber
I made a phosphor bronze 'inner push pin' against the ball valve. It is held in the coil spring and its tip has '+' section to let steam pass.
All of the whistle valve components.
Copper tube between the whistle and the valve should be arranged as short as possible. The tube goes through the running board without any contact.
The first steam test was done with propane cassette torch. I got well balanced three notes, however there were some problems.
1) With maximum steam pressure, the lowest note resonates in the third harmonic.
2) Pressure-controllability of the whistle valve isn't good.
3) It needs too much time to tuning each voice's pitch.
4) When it goes, hot water comes out through the valve pin.
5) Whistle valve lever becomes too hot to handle even with leather gloves.
To improve pressure controllability, I employed a needle valve instead of the ball valve. It was integrated with a straight shaft which is hold in the coil spring. It has 3 degree taper.
The needle was made of free-cutting stainless steel. After turning in the lathe, the taper part was burnished with emery cloth. The photo includes the outer push-pin. I made a groove around it and packed graphite yarn, so as to prevent steam leakage.
In order to ease tuning, I designed remote tuning method. A long screw from the bottom plug adjusts position of the half-round plate. As the plate isn't soldered permanently, you can tune it even after the loco is completed. The drawing shows lower whistle. Note a thin screw column holding rear end of the partition plate, and a small drain hole at the upper-left closed chamber to drain condensed water out.
So as to cut a stepped hole in the rear plug, it was chucked in the lathe three-jaw clamped onto the milling machine table. The center hole was reamed and the step was milled.
The adjusting screw was made of free-cutting stainless steel. It was fixed in the rear plug with E-ring.
For heat isolation of the valve lever, I employed a kind of heat-resisting plastics. It was turned in the lathe and fixed onto the original button by a set screw with epoxy adhesive.
Steam test was done again. After adjusting 'gaps', that of lower one note became 0.5mm, while those of higher two notes became 0.3mm. 'Remote tuning' works very well. For easier tuning, you can mute any note with a rag in the openings. After all of adjustments, the both plug were soft-soldered into the tube. But the remote tuning is still available.
I attached sound file here.
If you had never heard model-locomotive whistle voice, I guess it sounds cheap and imitate. So I present you the next - one octave lower voice of it.