Feeder

Feeder bellows

Here is a simple outline drawing of the feeder assembly as located inside and above the bottom frame of the cabinet.

Lowest are two double acting feeder bellows, actuated by connecting rods to a crankshaft. The crankshaft is driven either by an electric motor or alternatively manually from its other end. Right now I have mounted a hand crank here, but I may complement that with some bicycle pedal assembly - it is quite heavy work to supply the some 100 watts of power with your arms for an extended amount of time.

The moving boards of the feeders are mounted on welded steel frames (red) that have rubber hinges at the extreme left side of the cabinet frame. That way the feeder bellows move more like a parallel motion than in a plain wedge bellows, an expedient to maximize bellows air displacement while keeping size down. - After disconnecting the screw joints on the feeder frame shafts I can easily lift the entire bellows and crankshaft assembly out of the cabinet for maintenance.

The following image sequence shows details of the primary air regulation machinery, as parts are successively removed.

	The reservoir bellows is compressed by two leaf springs, hinged on yokes at their ends, defining the raw 3 kPa pressure. There are three different sensors of reservoir lid position: 1. Far right a potentiometer controlling bellows motor speed at normal use. 2. Middle, a string pulling an input regulator valve when an external feeder fan is used. 3. Left, a string to a pallet valve, pneumatically controlling the reservoir input valves when the unit is hand cranked.
	The four reservoir input valves have little piggyback bellows. When hand cranking at too high speed (alt 3 above) these hold the valves open, such that air flows back into the feeder bellows.
	On top of the floor is a frame divided into several compartments. Here are eight round intake flap valves. At center is the regulator valve to control the inflow of air when an external fan is used for supply.
	Below this 'floor' are the feeder bellows. These alternately suck and blow air through the three round holes and one rectangular.

Through the four numbered holes in the floor the feeders alternately inhale and exhale air. The lower two feeder halves are channeled up to the floor using 75 mm plastic tubes (holes 3 and 4). The central frame above the floor holds most valves in the system, next drawing. On top of that frame is the reservoir bellows. It is a matter of unscrewing four bolts to take out the reservoir and this valve frame for service.

An external fan is an additional air supply alternative. There is an inlet and back check valve for that in the valve frame and that air will then enter the central compartment of the frame. From there is a passage up to the reservoir, central dashed hole in the drawing. This hole is covered by a bellows unloaded disk, connected with a string and spring to the reservoir lid, works as a pressure regulator.

The springs to press down the reservoir lid used to be a bit problematic. Earlier i have used a set of harmonium compass springs for the purpose, but they were tricky to balance in order to have the lid moving in parallel. Next I followed a conventional design using helical springs with extended arms, tied down with straps. Heated and shaped an old athlete's arm strengthener made from 6 mm steel wire. Now finally, a pair of leaf springs, resting at the center of the reservoir top board and with yokes at their ends. These work very well to keep the board moving in parallel. Each spring is a stack of four 1*50 mm spring steel bands of progressive length up to 500 mm, same as the length of the reservoir.

This picture shows how pressurized air is distributed in the organ. Basically the long distribution lines carry the higher 3 kPa raw pressure. The tubes toward chests are 50 mm diameter while those for the harp, drums, and register unit are 32 mm. The regulators for 2 kPa are located as close as possible to the wind chests.

Here is a total view of the bellows assembly, with the drum machine riding on its frame. The hand crank is resting on the floor. Left of the middle floor you see the joints of the feeder bellows arms. The blue thing at right, below the open accessories drawer, is the battery. On the shelf, between that drawer and the keyboard, is the RD-70 MIDI player. A red and a green patch locate its stop and start buttons. At the right end of the shelf is a small brass box. This is the water container for a pressure manometer tube running up the adjacent pillar.