Now we come to a rather important unit called the governor.
The unit in my piano actually comprises a governor, accelerator, tempo control, and reroll bypass…here’s what it looks like!
(These are the “before” pictures)
So what’s a governor? What does it do?
A governor is essentially a pairing of a spring-loaded pneumatic and a knife valve. Its purpose is to regulate suction flow to the motor, so that the motor turns evenly at a given tempo.
Because the action of a person pumping the pedals is not always perfectly smooth, there needs to be a way to compensate for this roughness and the governor’s job to do so. Like other aspects of the player action it utilizes a simple yet elegant design. The flow is routed through the knife valve, which is open a certain amount (let’s say halfway, for the purposes of this explanation) under normal pumping.
If the pumper slacks off, slightly (too much slacking will make the music stop!), the governor compensates by sensing the flow pressure differential inside the unit, and opens the valve to allow more access to the main trunk, where there is extra suction stored in the reservoir.
If the pumper gets excited and starts pumping extra hard, again the differential is sensed and the suction pulls the pneumatic (and the valve) more closed, so that it doesn’t make the motor rush.
This all happens behind the scenes with no direct intervention from the user, it’s all automatic.
Without the governor, the motor (and therefore the playback of the music) would be completely at the mercy of the pumping technique of the user. In many cases, this would mean a bad performance!
The tempo control is commonly paired with (or in close proximity to) the governor. Every pianola has a tempo control lever, which is adjusted by the user. The lever is connected to a slide valve in the unit, which moves in a linear way over an inline port to the motor.
Essentially, when you move the lever to a higher tempo, you are opening the valve to let more suction reach the motor. When the lever is moved downtempo, the valve gets closer to closing, effectively choking the motor and slowing the music.
The accelerator is very much the same idea as the tempo, except in my piano it is meant to be used in “real time”, as opposed to the tempo control which is supposed to be set at the beginning of the roll. The accelerator is also spring loaded to default to a neutral position; whether you press the lever to “accel” or “ritard”, it will spring back upon relase.
Finally, there is a bypass valve, for reroll. When the roll finishes, the “play” lever is flipped to “reroll”, and a couple of things happen as a consequence. Firstly, the direction of the transmission is reversed, so that the roll rewinds. In addition, the suction to the stack is cut off, so that no notes are triggered upon reroll. We wouldn’t want to hear the music playing backwards!
The rotary valve is switched off (this valve is pictured back in the pedal pneumatic post); the signal to the pedal pneumatic is cut off, so that the damper lift is not triggered constantly as the roll rewinds.
Finally, the bypass valve in the governor unit is opened, so that the motor gets maximum suction and operates at full speed on rewind. Otherwise, it would take as long to rewind a roll as it would to listen to the song – and unacceptably long delay!
Even though the construction of the unit is fairly straightforward, it’s important not to overlook anything and to get it all right.
Make sure the knife valve is still mated well, and lubricate with graphite. Recover the slide valves if necessary, and lubricate those too (lightly). Recover the pneumatic and make sure it’s tight, before remounting on the unit. Ensure the various port channels and compartments are sealed, so that there is no inadvertent leakage when the valves are closed.
There really isn’t an obvious way (to my knowledge) of testing the governor’s function independently, outside the piano. So you won’t know what you’ve got until everything is back in place and connected up… but, if you have done diligent work, you should be fine!