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Organ Pipe PSI

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  • Organ Pipe PSI

    Hello all, I am new to the forum and was just wondering, what is the maximum pressure a flue pipe in general can use before it starts to overblow?


  • #2
    That depends upon a lot of factors. One is, how gentle is the attack? By that I mean, how gently does the air come up in the pipe? A quick attack will blow the pipe over on lower pressure than a slow attack. Because of this, a pipe voiced for a tracker chest can be voiced louder and brighter than one going on a chest with one valve per pipe, such as the average electro-pneumatic chest.

    It is a fact that you can put a pipe on a voicing machine, a pipe that is voiced for, say four inches, and then turn the pressure up considerably, which also increases the volume considerably, and that pipe will not overblow. But, if you tried to start the pipe on that pressure, it would certainly overblow immediately.

    Also, the languid position makes a difference. A pipe that has the languid placed for either a more octave sound (lower position) or a more "twelth" sound (higher position) will overblow sooner, the first obviously to the octave and the second one to the twelth.

    Finally, the size of the pipe makes a difference, with a larger pipe being able to handle far more air than a smaller one. Strings are notoriously susceptible to overblowing, thus the use of beards, rollers, etc in front of the mouths to keep them from exhibiting this behavior.

    My home organ is a Theatre III with an MDS II MIDI Expander.


    • #3
      As you are new to all this, I need to point out a couple of things to prevent further confusion:

      We measure the wind pressure on organs in inches or millimeters, not PSI. We use a device called a manometer. It consists of two verticle tubes, glass or clear plastic, connected by a U shaped tube on the bottom. A hose it connected to the top of one tube. We put the other end of the tube on a pipe hole or a hole in a wind line or bellows to measure the pressure.

      This pressure is very low. It would not even register on a tire pressure gauge. The highest pressure on any organ (100" at Atlantic City Convention Hall) would only be three or so PSI. Most organs are on less than six inches of pressure - most are on on three to four.

      Some types of organs use very low pressure - baroque and neo-baroque may be on less than two inches. Some types of organs are on high pressure - such as theater and orchestral organs where it is not uncommon to see an entire organ on six to eight inches with some stops on ten to twenty inches.

      Getting a pipe to overblow depends not only on what type of pipe it is, as Mike says, but what note. A pipe in a 4' rank an octave above middle C will overblow with less pressure than one in the lowest octave of a 16' rank.

      So, it is impossible to say which pressure is average. There is far to much variation. This is one of the great things about our instrument. The variety. NO twoare exactly the same.

      If you want to learn how the organ works, there are a couple of books which contain copious amounts of information and any large library should have them. William H. Barnes, The Contemporary American Organ and Stevens. Irwin, A Dictionary of Pipe Organ Stops.