How did the air-pressure of the church organs in 1600 work?

Answer 1

Organs of the period had what is now known as low wind pressure, typically between 2 and 3 1/2 inches on a water column. Some a bit lower and some a bit higher. Wind was raised by a man or men working bellows much like a common fireplace bellows but quite a bit larger. They were either pumped with the hands or feet. Sometimes several men were used to operate an array of bellows on large organs. The wind was conducted in rectangular wooden pipes to a reservoir or several reservoirs in large organs. These reservoirs held a reserve of wind for when many stops were pulled and large chords were played thus using more wind. From the reservoir(s) the wind then entered the wind chests upon which the sets of pipes were placed (in racks). The windchests contained a valve for each note on the keyboard. Individual sets of pipes were brought into play by moving long, narrow, thin, wooden strips called sliders. Each set of pipes had it's own individual slider. These sliders had one hole for each note / pipe and were sandwiched between channels, which had a valve for each note on the bottom, and boards upon which the pipes rested on the top (toeboard). The toeboards had holes bored into them to admit wind into the base of each pipe. When the sliders were moved so that their holes lined up with the holes in the toeboard, that set of pipes played. When it was moved so that their holes did not line up with the holes in the toeboard that set of pipes would not play - it was stopped from playing, thus the term "stop." The sliders were connected via levers and linkages to knobs mounted on the case next to the keyboard(s). Some modern organs still use this arrangement.