Moody-First UMC, Galveston.  Schantz Organ, 1997

Flue Pipe Construction

Metal Flue Introduction | Metal Flue Bodies | Metal Flue Mouths
Wooden Flue Introduction | Wooden Flue Bodies | Wooden Flue Mouths

Metal Flue Pipes: Introduction

Parts of a Flue Pipe Flue pipes (usually called simply "flues") have no moving parts. Their sound is produced when a stream of air is focused onto a sharp edge - - the upper lip of a flue pipe. As the wind strikes the lip, its smooth flow is disturbed. In the resulting disturbance, a vibration is set up in the air column contained in the pipe body, producing an audible sound wave. A similar structure and result can be seen in the mouth of a recorder, which produces its sounds in the same way.

Flue pipes have two primary parts, the foot and the body. Although these names are used for both metal and wooden flues, there are other differences in their construction, according to the material being used. These differences are examined in detail below.

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Metal Flue Introduction | Metal Flue Bodies | Metal Flue Mouths
Wooden Flue Introduction Wooden Flue Bodies Wooden Flue Mouths

Metal Flue Pipes: Bodies

The body of metal flues is typically circular in horizontal cross section, and it may be either cylindrical or conical in shape. The top of the body may be either open, closed or partially closed.

Coned Principal PhotoWhen the pipe is open, the end may be treated in one of several ways. The first method is to cut the pipe to the correct length to obtain the desired pitch. Because changes in temperature and the density of the surrounding air can have an effect on pitch, these pipes may be altered slightly by having the edges turned slightly out, or slightly in to modify the pitch. This approach to pitch modification is called coning or cone tuning, and must be done very carefully. The photograph shows two pipes from a 2' Principal that have been coned in opposite ways.11

Tuning Collar PhotoThe second treatment for the top of a flue pipe is to fit the open end with a movable sleeve or collar of metal. The collar is not fastened to the body of the pipe, but is held tightly in place by tension, leaving it free to be moved up or down to affect pitch changes. Even when the pipe is made of spotted metal, a thinner, less malleable sheet of metal is used for the collar, as seen in this photograph. 12

Tuning Scroll PhotoFinally, open pipes may have two small cuts made into the material of the body at the open end. The metal between the cuts may be rolled down to shorten the effective length of the body, as seen in the photograph to the right. 13 The resulting curl of metal is usually called the "scroll," and the process of tuning a pipe in this manner is referred to as "scroll tuning" or "scrolling." Alternately a separate, movable piece of metal can be fastened to the body of the pipe. This can then be moved up or down to make a similar change.

Metal Gedeckt PhotoWhen a metal pipe is closed at the top, it is usually fitted with a cap, which is slightly larger in diameter than the pipe and fits over the end. The inner rim of the cap is usually lined with felt, so that air pressure will not cause a rattle, and the felt is often folded over the outer rim of the cap and is visible. Closed metal pipes can often be recognized by the presence of a felt band marking the end of the cap, as seen in this photograph. 14

Chimney Flute PhotoTwo types of partially closed metal pipes are common. In the form seen at the right, an opening in the cap is extended by a smaller metal cylinder. 16 In some cases the cylinder is extended downwards into the body of the pipe. Pipes made like this are called in different languages Chimney flute, Rohrflöte, or Flûte à cheminée in description of their appearance.

Koppelflote PhotoAlternately, the cap itself may be made in a conical shape with an opening at the smaller end of the cone. The photograph to the left shows the conical cap of a Koppelflöte with the opening visible in its top. 17 A Spillflöte has a cap with a similar, more elongated shape.

Mitered Gemshorn PhotoAlthough most flues - - whether the bodies are made of wood or metal, or whether they are cylindrical or conical - - are straight, their bodies may in fact be mitered, or bent at one or more angles. These changes in the shape of the body are made only when space or other limitations must be considered. Mitering a pipe has only a small effect on the quality of the sound, but the change of direction in an open pipe can cause the projection of the sound to be different. In metal pipes, like the one in the photograph to the right, mitering can lead to instability in the body. If a soft metal is used (one with high lead content, for example), extra support must be provided or the pipe can be pulled apart by its own weight. The pipe in the photograph is made of zinc and is stable. 15

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Metal Flue Introduction | Metal Flue Bodies | Metal Flue Mouths
Wooden Flue Introduction | Wooden Flue Bodies | Wooden Flue Mouths

Metal Flue Pipes: Mouths

Flue Mouth Photo In metal pipes the foot is usually conical and expands from a small base to the point at which it joins the body. An inset plane around the joint between foot and body is called the face, and an opening into the pipe - - the mouth - - is cut into the pipe on that plane above the languid, an internal horizontal plate that almost completely closes off the foot from the body.

Languid and Lips Photo Wind enters the pipe through the toe, appropriately located at the base of the foot, and exits the foot through the flue, a narrow opening between the languid and the lower lip. These two parts focus the wind onto a relatively sharp edge called the upper lip.

A pipe mouth may have two additions made externally.

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Metal Flues | Metal Flues | Metal Flues
Wooden Flue Introduction | Wooden Flue Bodies | Wooden Flue Mouths

Wooden Flue Pipes: Introduction

Wooden Flute PhotoThe choice of materials has an effect on the shape a pipe assumes, and wooden pipes are most often square or rectangular in horizontal cross section. As the photograph to the left shows, even wooden pipes usually have a cylindrical extension at their base, and that extension will often terminate in a lead tip which allows the toe hole to be opened or closed without damage to the wood. 25

Two exceptions to wooden pipes having a rectangular shape are noteworthy:


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Metal Flue Introduction | Metal Flue Bodies | Metal Flue Mouths
Wooden Flue Introduction | Wooden Flue Bodies | Wooden Flue Mouths

Wooden Flue Pipes: Bodies

The body of a wooden flue may be either open, closed or partially closed, but the construction of the upper end of wooden pipe bodies is different from that found in metal pipes.

Open Wood PhotoOpen wooden bodies cannot be cone tuned, as can metal ones, because wood cannot be flared or coned inward to effect a pitch change without destroying the material. Sliding tuning collars are also not found on wooden pipes. They are instead fitted with a slot and a movable wooden slide that can be used to change the effective resonating length of the body. 26

Wooden Gedeckt PhotoClosed wooden bodies are usually fitted with a stopper made of wood and padded with leather. The stopper is made to fit inside the body and usually has a handle, or even a cord, attached to its top so that its depth can be adjusted. The photograph shows a typical stopped pipe with a stopper from another pipe beside it. 27

Wooden Flute: Scrolled TopPartially closed wooden pipes are made in several different ways. The most common way is found when a piece of metal is attached to one side of the top of a wooden body. The flap of metal is then rolled back, or scrolled, to partially uncover the top of the pipe. 28

A less common means of partially closing a wooden pipe is found in the case of wooden Chimney flutes. In these pipes, which are much less common than metal Chimney flutes, a hole is bored through the wooden handle of the stopper. The wooden Rohrflöte shown in the photograph to the left has been made by fitting a new wooden Gedeckt with stoppers from an older pipe. 29

Mitered Wooden Flue PhotoThe body of a wooden pipe by be mitered, or turned at an angle. Particularly in the case of stopped pipes, there is no change in the projection of sound, because the mouth, through which the sound is heard in a stopped pipe, can have the same placement as unmitered pipes in the same rank. If a miter is extensive, a wooden pipe can become unstable without support, as can a metal pipe. The photograph to the right shows one way of building a wooden mitered pipe so that there is little possibility for instability. The side of the pipe uses one piece of wood for both sections of the miter. A blue line shows the internal wall that separates the two sections, so that the body consists of one resonating space that has been folded over and covered with one piece of wood. 30

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Metal Flue Introduction | Metal Flue Bodies | Metal Flue Mouths
Wooden Flue Introduction | Wooden Flue Bodies | Wooden Flue Mouths

Wooden Flue Pipes: Mouths

The mouths of wooden pipes are generally built as a part of the body. The languid is replaced by the block, a piece of wood that is as wide as the interior dimension of the pipe body. This block of wood has a cylindrical hole drilled in its lower surface, through which the cylindrical foot is attached. Another hole is bored from the front of the block, intersecting the space made be the first hole. A small plate of wood, called the face, is attached to the front of the block. The face has a small amount of material removed from the side that will be in contact with the block. The small space fits over the hole so that wind can enter it. The wind then moves through the space between block and face and exits through the flue formed by the top of the face and the block.

Wooden Gedeckt, Block OpenThe photograph at the left shows two views of the mouth of a wooden pipe. In the first view, the mouth appears as it normally does in a working pipe. In the second, the face has been removed and turned over to show its back side. The shallow cut, which covers most of the area of the plate, is visible on the face. 31

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Metal Flue Introduction | Metal Flue Bodies | Metal Flue Mouths
Wooden Flue Introduction | Wooden Flue Bodies | Wooden Flue Mouths



© 1998, James H. Cook