Pallet and Slider Chests
|
Pallet and slider chests are most frequently found on organs with mechanical action linking the key to the chest. They may also be controlled through electrical connections which operate their mechanism through electromagnets. In either case pallet and slider chests have three sections, each of which serves a different purpose:
The pallet box is the lowest part of the chest, and wind is admitted to it from either a reservoir or a Schwimmer. The pallet box is fitted with a series of pallets, one for each note of the keyboard which controls the flow of wind from the pallet box. Each pallet is a small piece of wood, held in place by a spring. In its closed position, each pallet covers an opening into a separate key channel, which forms the intermediate section of a slider and pallet chest. A small wooden or metal rod, a tracker, is attached to each pallet.
When the tracker is pulled down, the pallet is pulled away from the opening, allowing wind to enter the key channel. When the tracker is released, the spring closes the pallet, and wind can no longer enter the key channel. In the alternate form of action used with these chests, the pallet is pulled open by an electromagnet, and when the current is released, the spring closes the pallet.
The diagram to the right
shows a cross section through a pallet box and a single key channel above it. The
brown
rectangle is a pallet, as seen from the side. The black arrow represents the
downward pull on the
pallet, which would be provided by a tracker or a magnet. As the pallet opens, wind
from the
pallet box (represented by the blue arrow) enters the key channel above. As the
force on the
tracker is released, the spring (red in the diagram) closes the pallet, and air can
no longer enter the
key channel.
The diagram above is only
a
cross section , showing one pallet in action. In practice, the pallet box is as long
as the chest of
which it
is a part, and it contains a separate pallet for each note on the chest. The
photograph to the left gives a view
of an open pallet box, with one pallet pulled down. The opening to the key channel
above the pallet can be seen above
the pallet itself. Pallet boxes have removable panels that allow access for
maintenance, and one panel
was opened when the photograph was made.
107 Without the panel in place, however, the
pallet
box is not airtight, and the chest cannot work properly.
The key channels run
perpendicular to the pallet box one level above it. They are separate from one
another, and each
one is connected to the pallet box by the opening controlled by the pallet. This
arrangement
means that playing one key from the keyboard allows wind to enter only those pipes
that are
above a single key channel. The diagram to the right shows a portion of a chest with
a view of
the pallet box and a row of key channels above it.
The first two sections of a pallet and slider chest - - the pallet box and the key channels - - allow control over which pitches will be sounded when a given key is played. The top section contains the slider mechanism, which allows control over which stops are sounded when that key plays. This topmost level itself has three layers:
The function of a slider is illustrated in the diagram to the left. The black strip
represents a
section of a topboard, with two holes represented by white circles. If nothing stops
it, wind in
the chest could exit through the holes. The green strip represents a slider, and it
first appears with
two holes that are not aligned with those in the top of the chest, stopping the wind.
As it
"slides" to the left, its holes gradually align with those in the top of the chest,
and they are once
again open - - now through the slider itself. In an actual chest, the topboard would
be in place
above the slider, but that part has been omitted from this diagram.
The diagram to the right shows a section through a similar slider mechanism as it
would be seen from
the front of a chest. The bottom and top parts
(black) are topboard and toeboard respectively, and they do not move. The middle
part (green)
is the slider and moves in the diagram from right to left. When it is to the right,
its openings do
not line up with those of the other two parts, and wind (the blue arrows) cannot pass
through.
When it is to the left, the openings are aligned, and wind can pass through all three
layers to the
pipes above.
The photograph to the left shows the slider mechanism
for a pedal chest on a small
organ built with pallet and slider chests.
105 The bright green A is placed at the
end of a row of sliders,
which are made of a thin synthetic material. The parts indicated by letters B
and C move the sliders
into position and are explained more fully on the "Mechanical Action" page.
106 It is important to realize that the slider
connected to the rod indicated by
the letter B is in the "on" position - - i.e., the slider has been moved to
the right as seen in this photograph.
The other sliders are in the "off" position, and they are not engaged.
When all three parts of a pallet and slider chest are in place, all pipes that are played by a single key are aligned over the corresponding key channel. In a line perpendicular to the key channel, all pipes of a given stop are in line with a slider that runs across all the key channels. Therefore, a pipe will sound only when both these conditions are met:
The diagram below illustrates a simplified chest that contains three ranks of pipes and 12 key channels. To avoid the appearance of a crowded forest of pipes, only the first three pipes in each rank are shown. The small green rectangle on the side is placed there as an indication that the slider for the second rank of pipes is in the open position. If the second key is played, the pipe that stands above both the second slider and the second key channel will play if the pallet below the key channel is opened. Both the second key channel and its corresponding pipe in the second rank are colored red for identification. Similarly, the third key channel and the corresponding pipe above it are both blue, so that pipe would sound if the pallet below the third key channel were open.
Two films of parts of a pallet and slider chest are available:
© 1998 James H. Cook
