Pipe Construction and Flap Valves

by Bruce Thompson

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As a professional organ builder I have been interested in the John Smith Busker organ for some time.  I have just completed my first organ but would like to suggest some modifications which I feel improve the organ and simplify the manufacture.

Pipe construction
I made the pipes in the traditional way with solid block and upper lip chiselled into the face of the pipe. Make a knife cut on the inside of the face equal to the cut up and when chiselling the slope for the mouth the cut gives a clean edge for the upper lip, slight rounding off of this will give a smooth tone.  The cut up should not exceed 1/3 the width of the mouth.

Flap valves
The valves in the bellows are too complicated on the John Smith plans.  The feeders need only four 16mm holes drilled in a square and a piece of leather glued over, at each corner.  It can be pinned if desired.  No backing is needed for this and these valves are what was used in the feeders of large pipe organs that were hand blown.  The same for the air inlet valve in the reservoir.  The overblow valve on my organ is on the inside of the top and is just a piece of plywood (5mm) covered with leather, the tail being glued to the underside of the top, and held in place with a small flat spring.  A hole is drilled into the flap and a nylon cord is looped round a staple driven into the bottom and passed through the hole in the overblow valve.

The height of the bellows is set and a small tapered plug is forced into the hole to hold the nylon secure. When the bellows reaches its limit, the nylon pulls the valve open and allows the pressure to escape.  This keeps the top of the reservoir clear and the two upper notes of the bass pipes can be fastened to this. In addition I drilled a hole directly into the top of the bellows at the hinge end, and used a flexible hose to convey the wind directly to the pressure box.

Bruce Thompson & Associates, Pipe Organ Builders

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