Pitman Windchests Explained

The key channel is an enclosed conduit built into the walls of the chest, and it serves all the pipes belonging to one key; the stop channel runs perpendicular to it, with one stop channel for each stop and one pitman for each note. Picture the key channels as one set of parallel bores and the stop channels as a second set crossing them, so that every place where a key channel meets a stop channel corresponds to exactly one pipe. Because the stop channels are built into the chest for a fixed number of stops, the chest’s internal division is settled when it is made, and the pouches and pallets sit above the crossings, directly beneath the toe holes in the topboard.

Above each crossing, a pallet held by a leather pouch seals a hole in the topboard, the drilled surface on which the pipes stand with their toe holes aligned to the board’s openings. The pouch is a flexible leather membrane that is pressed down when the wind beneath it is exhausted, and when the key channel behind it is emptied the pressure difference collapses the pouch, the pallet comes off its seat, and wind enters the pipe foot. Nothing about the pouch knows which stop it belongs to; it responds only to whether wind has been let out of the space beneath it, and the pitman is what decides whether that exhaust ever reaches it. The pallet page covers the valve itself as a component across chest families.

The pitman is a small metal cylinder with a leather pad attached, and it is the stop-selection element: it decides whether wind admitted for a given key reaches a given rank. Each stop channel carries one pitman for each note or key that can sound a pipe on that chest, so a chest built for a given number of stops carries that many pitmans for every note, one in each stop channel. The stop magnet governs the stop channel, and the state of that channel sets the pitmans along it. James H. Cook’s 1998 description, hosted by the Organ Historical Society, puts the condition plainly: a pipe sounds only when the selected stop has raised the corresponding pitman and the played key has exhausted the key channel.

The action is a two-condition gate: R. E. Coleberd describes it as an x, y switch in which both x for the stop and y for the key must be on before the pipes will speak. Neither signal alone does anything audible. A drawn stop with no key pressed sounds nothing, a pressed key with no stop drawn sounds nothing, and only the pipe at the crossing of an active key channel and an active stop channel receives wind, while every other pipe on the chest that shares that key or that stop stays silent. This property is what gives the chest its behavior, and it is what the later sections of this page trace into layout and into fault patterns.

The electromagnet does not move the pipe valve. In an electro-pneumatic chest the electrical side only controls the access of organ wind to the moving parts, and the pneumatic side does the work of admitting wind to the pipes. Energizing the magnet moves an armature, in the classic form a horseshoe electromagnet attracting a small armature disc, and that armature vents a small channel. The pressure difference the vent creates is what collapses a leather pouch, in that description about two inches across, or a small rectangular bellows, and that collapse is what opens the pipe valve. The magnet’s own contribution is only the vent; the wind does the work.

The primary is the small pneumatic that the magnet’s vent acts on first, and the secondary is the larger motor that opens the pipe valve. In the ready-made form catalogued for the trade, a replacement primary is a small pneumatic on a wooden block, covered in thin pneumatic leather, with a valve wire on one side and a gasketed port on the other, which is the shape of its job: a small leather motor carrying a valve that controls a larger channel. In a pitman chest that larger channel is the key channel, and supplier literature treats one primary as serving that key channel across the stops on the chest, up to a stated limit. The sequence, then, runs magnet, vent, primary, key channel, pouch, pallet, with the pitmans deciding along the way which pouches are permitted to respond.

Alan Jackson, writing on servicing Casavant organs for the Journal of American Organbuilding, describes the Casavant distributor action of the 1920s as built from removable blocks, each containing a primary and a secondary pneumatic, and observes that the eggshell-type lambskin used in them has about double the life of the pouchboard leather. That is one named technician’s field observation about one builder’s action of one decade, given without measured figures in an undated article, and it is quoted here because it shows the two stages as physically distinct parts rather than as a way of speaking.

Electro-pneumatic chest action uses two distinct pneumatic motor forms, and both work on a pressure difference across leather. The pouch collapses when the wind beneath it is exhausted; the small rectangular bellows, the other form, collapses when the wind inside it is exhausted while chest wind surrounds it. In the pitman chest, pouches hold the pallets above the toe holes and the primaries are leather pneumatics too, so the action is leather from the magnet’s vent to the pipe valve.

New chests built to order are still described this way: the wholesale supplier’s catalog page offers chests furnished as Pitman, Unit or Electro-Mechanical Unit, in poplar and voidless basswood plywood, with all pouches and primary pneumatics covered in pneumatic leather and Reisner magnets in the electro-pneumatic chests, as published on the page at the time it was read, with no statement of per-item stock.

The primary channelling can sit in more than one place in the chest, and its location is one of the ways pitman chests differ from one another. Organ Supply Industries, in a catalog section carrying a 2006 copyright and a 2014 revision, offered pitman chests in three design styles distinguished by exactly this: style 1 places the primary channelling in the bottom boards, style 2 in the toeboard, and style 3 in the top table. The logic of key and stop channels is the same in each; what changes is where the primaries and their channels live, and therefore where a technician reaches them. Skinner’s own revision, described under the design’s history below, moved the pouches onto a removable board directly under the toe holes, which is a decision of the same kind.

One pitman chest serves a bounded number of stops, and the bound comes from the primary. Organ Supply Industries specifies that a pitman chest primary will accommodate up to 10 stops and that two chests are required for 11 stops or more, which sets a physical limit on how many ranks one pitman chest can carry. That limit is one reason a division with more stops than that occupies more than one chest rather than one. The same catalog lists both pitman and unit chests as operating at wind pressures as low as 2 inches, and it recommends primaries on unit chests for toe holes above a stated size; those are supplier specifications from a section revised in 2014, not a statement about any particular instrument or about what the supplier stocks today.

Not every chest in an electro-pneumatic organ is a pitman chest. Offset chests carrying a single stop, and unified or duplexed chests, dispense with internal pitmans altogether and rely on relay switching instead, so a Möller of the pitman era will normally contain more than one chest type. Cook’s 1998 tutorial puts the rule generally: offset and unified chests use switching and relays for stop selection, and the internal pitman mechanism belongs where several stops share a chest. The pitman logic applies to the main chests where stops sit side by side; it does not apply to an offset chest carrying a single stop, or to a unit chest whose rank is drawn at several pitches.

One documented instrument shows how mixed this can be. A monograph on the 1924 Kimball KPO 6763, a Scottish Rite auditorium organ, records roughly 40 percent of the pipework on unit windchests, which permit the same rank at multiple pitches, and the remaining 60 percent on pitman windchests, which do not. That is one hybrid commission rather than a proportion to carry onto church work, and the monograph itself is an undated enthusiast document. How unit, duplex and offset chests do their switching belongs to the unit, duplex and offset chests page.

Whether a single fault affects one pipe, one note across several stops, or one stop across the compass is determined by the chest’s channel geometry. In a pitman chest the key channel serves all pipes belonging to one key, the stop channel runs across it with one pitman per note, and each pouch and valve belongs to a single pipe, so a fault in a key channel, a fault in a stop channel, and a fault at one valve produce three different audible patterns because each sits at a different level of the crossing.

The same logic runs the other way for a pipe that sounds when it should not. On a chest with a common tone channel, all the pipes on a given key cypher together, though some may be more sensitive than others; on a pitman chest an individual pipe can cypher from dirt under its own pipe valve, and only when all the pipes on the key cypher does the source lie in the key action.

What the geometry does not do is name the cause in a particular instrument. The pattern tells a listener which direction of the chest is implicated; establishing what has actually failed, whether leather, dirt or something else in the channel, requires access to the chest, and locating it is technician work outside the scope of this page. The pattern is still worth recording when it is heard, with the note, the stop and the manual, because it is the one observation that can be made without opening anything.

Leather is the moving element of a pitman chest, not merely its seal. The pallets are held by leather pouches whose collapse under a pressure difference is what opens each pipe valve, so the leather is the consumable, working part of the action rather than a gasket around it; that is why releathering is the characteristic major work on a Möller windchest of this construction. The same holds for electro-pneumatic action generally: the pouch is the element the magnet controls, so the condition of the leather determines whether a note sounds at all, not only whether the organ leaks.

In a pitman chest that dependence is multiplied, because every note on every stop has its own pouch, and the primaries that serve the key channels are leather pneumatics too. The condition of the leather in any given chest is a matter for inspection; this page only explains why the question arises.

Pitman construction identifies a design, not a builder or a year. The word universal, for instance, is not exclusive to Austin: the pitman chest is itself described by other builders as a universal windchest, on the ground that admission of air to the pipes does not depend on switching the blowing supply on and off, so hearing an instrument called universal does not settle whether it has an Austin Universal Air Chest or a pitman chest. A general reference account adds that pitman windchests are less flexible in operation than direct electric action and that electro-pneumatic action using unit windchests works similarly to direct electric action, which is a comparison of behavior, not a dating tool.

Design generations are just as loose. A monograph on Kimball KPO 6763 states that all Kimball organs built after 1918 used electro-pneumatic chests similar to the pitman chest design; that is a single source, the phrase similar to is doing real work, and the same document records that the 1924 instrument mixes unit and pitman chests, so after 1918 does not mean pitman throughout. Which builder made a chest and when is a question for the instrument’s documentation and for people who can examine it, not for the chest type alone.

The combined key-and-stop channel predates the name. August Friedrich Herman Gern filed a British patent on 6 November 1883 for Improvements In Organs And Similar Wind Instruments describing a combined key and stop action channel, and R. E. Coleberd, writing in The Diapason in 2003, identifies this as the origin of what later became known as the pitman action. Ernest M. Skinner refined the principle by substituting a pouch valve for Gern’s piston valve. One historical account of the Skinner company dates Skinner’s pitman stop action to 1898 and describes it as an arrangement that let stops work as fast as notes, unlike the ventil system it replaced; the ventil windchest page explains that stop action, which works by switching the wind supply to a stop on and off.

The name has two documented explanations, and they are not the same story. Coleberd’s account has the name applied by Audsley from the image of a leather disc on a wooden stem moving in an orifice. The Organ Historical Society states that pitman derives from mining terminology for a connecting rod and credits Ernest M. Skinner with applying it to organ actions, citing a letter quoted by William H. Barnes. Both are documented attributions rather than a settled record, and this page reports them side by side.

The chest most people picture as a pitman chest is Skinner’s revised format. Beginning in 1909 Skinner revised the chest to eliminate the lever arm, moving the pouches onto a removable board directly under the toe holes with the pitman action attached below; the resulting format was the basic Skinner and Aeolian-Skinner chest as built until the late 1960s, according to the same historical account of the company. Other builders arrived by their own routes. Casavant Frères states that in 1895 it patented its first slider-less windchest, which it describes as the precursor of the Pitman-type windchest, and that its first use of a Pitman-type windchest was in 1914; that is the company’s own account of its history, given without patent numbers or filing dates.

Builder practice differs in detail. Alan Jackson’s article on servicing Casavant organs states that on Casavant pitman actions from after about 1930 the exhaust channels are in the topboards between the pipe holes, and that the stop action either runs up to the topboard and back down to the pouchboard or uses a short detachable flexible tube going directly to the bottom of each pouchboard. That describes Casavant’s own layout, in an undated article without drawings, and it is not a template for every builder’s chest; it is included because it shows how far a pitman chest can differ in construction while keeping the same crossed-channel logic.

Because the stop count, the placement of the primary channelling and the position of the pouches are fixed in a chest’s construction, they are the things worth recording when an instrument is documented: which chests are pitman chests, which are unit or offset, and how each is built. That record is the starting point for any inspection or project planning that will open them.