Pitman Chests

Of the several applications to electro-pneumatic power to organ chests, the one that is used today by most organ builders is the pitman chest. The name "pitman" is occasionally capitalized, and when it it, the implication is made that the word derives from the proper name of the inventor. The word is older than organ actions, however, and originally was a mining term, referring to a man who worked in a pit. The word was then applied to a connecting rod which transferred action of mining tools to another level of a mine. Only later was it applied to organ actions by Ernest M. Skinner, according to a letter quoted by William H. Barnes. ⁷⁵

The graphic image below is a simplified diagram of the cross section of a pitman chest as built by the Schantz Organ Company. ⁷⁴ Different parts of the chest are shown in contrasting colors for clarity.

• The structural outlines of the chest are shown in black, and the break in the top boundary of the chest is a hole in the topboard that leads to a pipe.
• The blue areas are parts of the chest that contain the wind when no stop is drawn and no note is played.
• The yellow rectangle near the top is the pallet, a small disc that closes the hole in the topboard.. It is held in place by a flexible leather membrane, the pouch, represented by the yellow lines attached to the pallet.
• The rose colored shape below that is the pitman itself, a small cylinder or square rod with another disc attached to its lower end.
• The red shape at the bottom of the chest is a rod with two leather seals. It too is attached to the chest by a flexible leather membrane, represented by two red lines.
• The green inverted "U" shape is the magnet, which moves a small disc or armature immediately below it, also green in the diagram.

When wind is supplied to the chest, the pressurized air moves through a small opening between the arms of the magnet. From this point the wind enters the key channel, an enclosed portion of the chest that is basically a conduit built into the walls of the chest itself. The key channel eventually leads to all pipes controlled by a single key. When an electrical circuit is completed by pressing the key, it first energizes the electro-magnet, illustrated in the diagram to the left by a slight change of color. When the magnet is turned on, it raises a small disc-shaped armature that has been held in place both by gravity and by air pressure in the chest. As the armature is raised, wind in the key channel can then escape, as indicated by the blue arrow. The air in the key channel then remains at room pressure as long as the magnet holds the armature up, closing off access of wind to the channel. If the key is released, and the magnet is no longer holding the armature, wind in the chest pushes the armature down, and air in the channel is once again under higher pressure from the wind in the main part of the chest.

The key channel first leads to a small chamber within the main part of the chest. This chamber is separated from the main body of the chest by a flexible membrane that is in turn connected to a rod and two seals. In the diagram to the right, all three parts are shown in red. When the chamber above the membrane and rod is under the same pressure as the rest of the chest, gravity holds them in the lower position, and the seal at the base of the rod prevents the wind from leaving the chest. As the air from the first section of the key channel is exhausted, the small chamber that it leads to is left without pressure. The absence of pressure in the chamber allows the wind in the chest to raise the rod and seal assembly. As the rod is lifted by the wind pressure, the second portion of the key channel is opened, and its wind is then released to the room. As the two arrows imply, this opening is larger than that at the base of the magnet, and a greater quantity of air can leave the second channel than leaves the first.

It is easier to understand the next action in a chest of this type if the pitman itself is ignored. In the diagram to the left, the yellow rectangle is the pallet, a small disc of felt or similar material which is held against the bottom of the hole in the topboard by wind in the chamber below it. The pouch is attached to the upper walls of this chamber by a flexible membrane, the pouch, usually made of leather. When wind is exhausted by the action of both the magnet and the rod assembly, the pressure is reduced, allowing the pressure above the pouch to press it down. This pulls the pallet away from the hole in the topboard, open it to the wind in the chest. Wind can then enter the pipe, which rests above the chest with its toehole aligned with the hole in the topboard.

Electro-pneumatic chests of this type, in which there is no actual pitman, are used in two instances:

• When a chest is built to hold the pipes of only a single stop, a suitable arrangement of switches and relays can make an internal stop action - - which uses a pitman - - unnecessary. Such chests are sometimes built to hold larger pipes, particularly those in a pedal division, when placing them on a main chest would cause unnecessary crowding. Small single-stop chests of this type are called "offset chests."
• When unification or duplexing is used, each pipe is provided with a magnet and valve, and switching and relays again make the use of internal stop action unnecessary.

When several ranks controlled by different stops are present on one chest, however, the use of an internal mechanism is needed to direct wind to the desired stops. This mechanism is found in the stop channel, a wind passage that runs perpendicular to the key channels. One stop channel is made for each stop on a given windchest, and the function of each type of channel can be compared to the analogous parts of a slider and pallet chest.

• Wind is admitted to the pipes associated with a specific key
  • By the key channel in a pitman chest.
  • By the pallet in a pallet and slider chest.
• Wind is admitted to the pipes associated with a specific stop
  • By the stop channel and pitman in a pitman chest.
  • By the slider in a pallet and slider chest.

The diagram to the right illustrates the movement of the pouch when a pitman stop mechanism is present. In the diagram, the pitman is a rosy pink rectangle located at the base of the stop channel, a chamber located below the pouch (yellow in the diagram). In this view the stop channel is seen from the end, while the key channel is seen from the side, as in the diagram above. Both gravity and wind in the stop channel above the pitman hold it in the lower position, and it blocks any exit of wind through the key channel below it. When wind in the stop channel is exhausted - - through the action of another magnet, wind presses the pitman up, leaving a clear passage from the pouch to the key channel. When a second magnet opens the key channel, the pouch collapses as in the diagram above, and the hole in the topboard is opened.

The diagram below shows a cross section of a pitman chest with two stops. The light aqua rectangle through the hole in the topboard on the left is included to show that the key channel continues behind the hole to the second pitman. In the illustration,

1. a stop control exhausts wind from the stop channel on the right, and the pitman moves up. The pitman in the stop channel on the left does not move.
2. When the magnet is turned on by pressing a key, the movement of the armature and the rod and seal assembly exhausts the wind from the key channel.
3. Because the pitman blocks the exit of wind from the pouch on the left, it does not move, and that pipe will not sound.
4. The pitman on the right, however, has been raised, wind can exit the chamber below that pouch, and the pipe above it will sound.

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