Fig. 5. Tubular Pneumatic Action
The tubes, N, from each key are fixed to the hole connected to the small puffs P in the puff-board E. Air under pressure is admitted by the key action and conveyed by the tubes N which raises the corresponding button valves S1, lifting their spindles S and closing the apertures T2 in the bottom of the wind-chest A, and opening a similar aperture T in the bottom of the cover-board F, causing the compressed air to escape from the exhaust bellows M, which closes, raising the solid valve H in the cover-board F and closing the aperture J1 in the wind-chest A, shuts off the air from the bellows, which immediately closes, drawing down the pallet B, which admits air (or wind) to the pipes.
No tubular-pneumatic action is entirely satisfactory when the distance between the keys and the organ is great. This is often due to a law of nature rather than to imperfection of design or workmanship.
Pneumatic pulses travel slowly—at a speed which does not reach 1,100 feet per second. In large organs where necessarily some of the tubes are short and some have to be long, it is impossible to secure simultaneous speech from all departments of the instrument, and in addition to this the crisp feeling of direct connection with his pipes, which the old tracker action secured for the organist, is lost.
It is generally thought amongst the more advanced of the builders and organists qualified to judge, that the tubular-pneumatic action will sooner or later be entirely abandoned in favor of the electro-pneumatic action. Certain it is that the aid of electricity is now called in in practically every large instrument that is built in this country, and in an increasing proportion of those constructed abroad.