Tracing and Curing Air Leaks

by John Smith

The first and biggest problem is to locate the source of any leaks, with so many parts this can be a bit baffling.  It is my experience that leaks are either quite obvious or a complete mystery, so how do we solve these mysterious ones?  One very useful piece of equipment is a piece of flexible tubing, say 1/4 inch diameter.  One end is held in the ear, the other moved around inside the organ, the smallest leak would be amplified and become obvious. The bellows not only provide the wind, but with their moving parts are also likely to be a source of leaks.

Before starting any remedial work, run a check on and note just how the wind supply is performing.  Tape up the tracker bar, then turn the organ at normal speed, if the reservoir fills up then fine.  Slowly reduce the cranking speed until the reservoir just starts to drop.  Maintain this speed, noting the number of revs per minute needed.  Any improvements you make to the non-playing organ will reflect in this.  If there is a problem and you suspect the bellows then it is best if they can be isolated. Disconnect any pipes from the bellows, and seal the openings with Plasticene.  Repeat the slow cranking test, note when turning whether the bellows are all giving the same pressuire on the handle.  In this way, a particular feeder section can be isolated.  All feeders should feel the same, check the spill valve for possible leaks.  If the bellows have to be removed then it is most important to be aware of the dangers from the spring.  Remove and replace this very carefully.  Make no attempt to re-crank the organ until it is properly positioned.  Most problems with bellows will be seen at the corners and gussets where the most flexing takes place.  Pieces of thin soft sheepskin leather can be glued over any holes that occur.  With the bellows out of the organ it is possible to pump each feeder by hand and feel the air transferring into the reservoir, this can be likened to the brake pedal on the car.  If it feels soft and spongy then something is wrong.  If the external leaks do not sort out the bellows, then internal faults may be the problem, but to deal with those is beyond the scope of this article, and probably best left to an expert. A good set of bellows should pump up evenly from its feeders, and sustain pressure in the reservoir for at least 10 seconds, with only about 6 revs per minute to maintain it. One way not to test bellows is to put them in the bath and watch for bubbles!  I actually saw the result of this once, not a pretty sight.

With the bellows working properly, reconnect the hoses one at a time and repeat the slow crank test, there should only be the slightest change. If the windchest seems to leak, check for any cyphers.  If there are any then give the organ a good shaking!  If this does not work then very carefully wiggle the valve stems, which may dislodge any foreign bodies in the seals, do not be tempted to twist or readjust anything.  Finally uncover the tracker ber and play through the test roll.  Listen to the individual notes, if any pipes are loose you may hear air escaping as well as the note.  Repeat notes should sound positive, not merging into one another.  Blocked up bleed holes can cause the organ to use a lot more air than normal.

Practical Modification
If you have an organ that has always been short of wind, or some particular roll that just has too many holes in why not try my simple modification.  This can be easily fitted to most instruments, without interfering with the original works.  What is needed is an extra coil spring or even rubber bands, a piece of string (or better still wire) and a couple of curtain wire screw-in eyes.  The idea is to relieve the pressure in the reservoir as it starts to empty, many reservoirs actually increase their pressure as they fall.  The string and spring assembly is fitted so that with the reservoir fully open it has no effect, but starts to stretch when the reservoir drops perhaps half way.  The effect is an organ which, instead of suddenly running out of wind, gradually becomes softer, a much better effect.  It is even easy to vary the effect by having more than one fixing point for the string!

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