Here you have treble keys,
and treble air valves
When a treble key is pressed, the keyboard mechanism activates a lever that opens the air valve for this particular note. The register mechanism controls two other valves beneath the upper visible valve, one for each set of reeds. Depending on which register button that is pressed, the air can flow through either hole 1 or 2 or through both. The holes are leading air through the reed blocks to the reeds.
On this picture I've removed the upper valve (I've put it beside the treble keys). You could see the two air holes, where one is open and one is closed - this is one of the three possibilities using a register mechanism with two sets of reeds. (It may also be possible to manouvre the mechanism in such a way that both holes are closed, although this would be meaningless)
On the other side of the valves are the reed blocks.
On this accordion there are three reed blocks on the treble side. Each reed block has two sets of reed plates for 14 notes each. There are 42 (3*14) possible notes on the treble side.
Alan Polivka (email@example.com), who very kindly has helped me checking the text, wanted me to point out that a 2-reed PA would only have 2 reed blocks in treble side, whereas this 2-reed chromatic has 3 blocks.
Here's one of the reed blocks.
The block could essentially produce 14 different notes. There are two air holes for each note and a set of reeds for each hole. The two sets of reeds may be combined in three different ways using the treble register buttons.
There are 14 reed plates on this side and another 14 on the other side.
Here's one of the reed plates.
There are two reeds on each reed plate, one for each direction of the air-flow depending on whether you're pushing or pulling. A skin is attached to each reed on one of the sides. The skin is attached in one end using shellack. The skin (could also be made of plastic) ensures that the air only flows through one of the reeds at the time. On the picture above, the right reed is covered by a skin. The left reed has its skin on the other side of the reed plate, inside the reed block. The reed plates are attached to the reed block using a special kind of wax. The wax ensures that there's no air leakage that would steal air that should be used to produce sound. Sound is produced when the air is allowed to flow through the gap between the reed and the reed plate, causing the reed to vibrate.
This is a free reed, the kind of reed that is used in accordions. The frequency is depending on the length and the thickness of the reed.
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Hans Palm 1997, firstname.lastname@example.org , snail address