Windchest Renovation
Windchests are basically pressurized boxes with holes upon which the pipes sit. A valve inside the chest opens to allow the air to flow into the pipe and make the pipe speak.
The windchests in our possession originally had a two-stage electropneumatic action that was amazingly complicated for the simple purpose of opening a valve to let pressurized air into a pipe. Basically, a solenoid opened a valve which exhausted the pressure inside a small bellows. The bellows then collapsed, pulling open another valve that exhausted the pressure inside a "pouch" upon which a leather pad was mounted that kept the pipe hole closed. Air pressure inside the windchest then collapsed the pouch and opend the valve so the pipe could speak. (That was a rather simplified version of how the beastie actually worked. Hopefully I'll have a complete explanation, with appropriate diagrams, in the not too distant future. In the meantime, there is a moderately good explanation of electropnuematic windchests, with animated graphics, here.)
Given the complexity of the electropneumatic action, and the facts that the leather in many of the bellows was cracked and the lead (yep, pure lead) tubes connecting the bellows to the solenoids were corroded, cracked, and bent, we decided to convert the chests to direct electric action. (The purists out there will probably cringe, but this is a student project with limited expertise and resources, and restoring the original mechanisms would have been a daunting task.)
With direct electric action, the valve that opens the hole to the pipe is directly connected to a solenoid. The solenoid is activated, and the valve opens - MUCH simpler. For larger pipes, direct electric action does not provide proper intonation (which I do not really understand), thus these will be refitted with direct electropneumatic actions that combine the pouch and exhaust solenoid all in one unit that mounts directly over the pipe hole.
Below are a few pictures of the refit of one of the windchests.
M. Sprague installing the direct electric valves. The board on top of the windchest is part of the original electropneumatic action. The box with the orange clamps at top right is destined to be a speaker enclosure.
The end of the windchest with direct electric valves installed. The large hole in the end is where the ductf rom the blower attaches to provide wind pressure to the chest.
One of the direct electric valves in place. Wires still have to be run to the relays. The debris will need to be cleaned out before closing the chest to prevent bits of wood from causing leaks past the valve pad.
The diode soldered to the two terminals is there to dissipate the current generated when the valve is turned off and the magnetic field collapses. (It is a fact of nature that when a conductor is placed in a changing magnetic field, a current is induced in the conductor. Without a means to dissipate (as heat in this case) the energy stored in the magnetic field and converted to electric current as the field collapses, sparks would fly somewhere - a bad idea.)
The keying cable in place, awaiting clamps to hold it in place. (The tape will be removed.)
The ground return still needs to be added, and a through-chest connector installed to connect the internal cable to the cable that will eventually come from the console.
Also, there are still various holes in the chest associated with the original action that will have to be sealed.
This page last updated at
CHORD site maintained by Dr. William Park. Please address comments or suggestions to parkw@ces.clemson.edu
