This is the foundation of the pneumatic stack, and is the operating unit, one of which actuates each section of the piano action. As shown in illustration No. 4, page 9, the pneumatics are arranged in three banks, each bank furnished with an interconnecting reduced-pressure chamber. All three chambers connect by a suction tube with each other and with the bellows system.
The unit consists of a pneumatic, or small bellows, contacting the piano action, on top of which is placed a valve block which, when it is pressed down (see upper illustration), shuts off the open air from the pneumatic and connects it with the reduced pressure chamber. When the valve block is up (see lower illustration) it shuts off the reduced-pressure chamber and allows air to enter the pneumatic. In the first case, the pneumatic collapses, because the pressure of the air outside its moving wall overbalances the reduced pressure of the air inside the pneumatic, said reduction taking place when the air in the pneumatic flows out into the reduced pressure chamber, until the pressures in the two places are balanced. It is understood in these explanations that the bellows are working, and that therefore the air is being sucked out from the reduced pressure chamber all the time.
It is the motion of the pneumatic's moving wall, in the process of closing, which operates the piano action (see illustration No. 4 again).
The valve block is caused to assume either the up or down position by the small "valve pneumatic." This is an exclusive Schulz feature and is considered superior to all forms of disk valve, owing to its greater flexibility of action and more rapid movements. It is caused to operate in the following manner:
Suppose the pneumatic at rest, as in the lower illustration opposite. The tracker duct is, therefore, sealed at the tracker end by the paper of the music roll. Note the little "vent," or small pierced cup, running into the interior of the valve pneumatic. When the bellows are being worked there is a partial vacuum; that is, a state of reduced air pressure (thin air) in the chamber. Therefore, the air in the tracker duct and interior of the valve pneumatic flows out into the chamber through the vent, till the ... [end of page 9]
Illustration 3 at high-resolution: mschulz3.gif
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