Restoration of a Duo-Art Expression system for Skyp Harmon
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1) The first five photos in this layout are simply pictures
of the mechanism as it arrived at the shop.
2) This mechanism goes in a Steck grand piano. The owner is simply having the
reproducing mechanism rebuilt in my shop.
3) The pump is not in these photos as the owner has opted to attempt rebuilding that
himself.
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4) Since this is a relatively small project, I will be doing
it fairly immediately rather than putting it at the end of the rebuilding queue.
5) When finished, these parts will be mailed back to the owner who lives in Ohio.
6) Now the work of rebuilding this system begins. This is the valve box which
controls the expression settings of the accordion pneumatics on the expression regulator.
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7) The valve box has been torn down here. As I take
parts off, I clean them up, repaint them and reseal them before I take off the next item.
All the nipples, screws, and support brackets on this system which are either
nickel plated or brass will be buffed to a high polish. Although the pouches look
like they may be in good shape, they are typical of the condition of these pouches in
other, similar, instruments. It is all an illusion. The leather is rotten
enough that it is impossible to get it to seal properly. So, although you might be
tempted to reuse them since they look solid and feel strong, they really can't be reused.
8) All the inside seats throughout the mechanism will be pulled, cleaned and
resealed with burnt shellac for all valves having round seats. All the cross shaped
valve seats will be pulled and discarded. I will replace those with round valve
seats which will be seated into burnt shellac. All air channels and pouch wells get
a fresh coat of sealer as well.
9) Replacing the valve leather. The leather on these valves looks pretty good
but it really isn't. Careful examination reveals that it is starting to rot even
though the gray original stuff looks pretty good at first.
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10) The finished control valve box.
11) This control valve was photographed before work began but, somehow, the camera
corrupted the photo and it was lost. The valve has been taken apart, all new valve
seats are ready to go in, all air channels are resealed, new valve leathers installed as
well as new pouch leather. All pouch leather throughout the system will be sealed
with Dow 111 instead of rubber cement. The Dow doesn't leave the pouches looking
lightly dusted like the rubber used to because its silicone base doesn't require dusting
off with talc. The Dow 111 will seal the pouches better and stay put as well as
protective for a longer period than the rubber cement could do.
12) All the separate components have been restored and the valve can now be
reassembled. While the pouch sealer and glues dry, I'll move onto releathering the
stack manifolds.
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13) The manifolds before I restored them.
14) The gasket surfaces have been cleaned and trued up and the external surfaces
have been repainted.
15) The valve from #11-12 is mostly back together and the manifolds have been
releathered. I like to use medium weight bellows cloth to recover all the control
valves and stack tiers in Duo-Arts. The lighter weight pneumatic cloth that was
often used at the factory doesn't hold up. It is usually crumbling long before the
pouches and valves need to be redone. The heavier cloth ensure that the valve will
remain air tight and free from any needs for service for a much longer time this way.
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16) The finished control valve.
17) The play/rewind control valve before work began.
18) Play/rewind taken apart and some of the restoration done.
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19) The restoration is done and it is almost ready to put
back together. I just need to let the pouch sealant dry a few more minutes first.
20) The finished play/rewind valve assembly.
21) The action cut out control device before work began. The "T"
nipple is pot metal. However, it still has plenty of strength left in the metal.
To reinforce it and prevent any further deterioration, the inside of the nipple
will be sealed with thick shellac and the exterior will be polished with steel wool and
then coated heavily with lacquer.
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22) The valve all taken apart and restoration well underway.
23) The finished valve after it was reassembled.
24) This assembly contains the tracker pneumatic, expression cut out block and a
complex control valve assembly.
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25) Here is the expression cut out before work began on it.
26) Here it is taken apart. It wasn't in bad shape but it will get the works
anyhow. The cover boards have been resealed with lacquer. The old pouch
leather will be replaced to ensure that I can get it to seal well.
27) I have a technique for these expression cut out blocks. They were
originally sealed shut with an external strip of light pneumatic cloth about 3/8"
wide. This seal cloth dies long before the expression's pouch leather does. To
make it easier to service and eliminate this problem, I increase the amount of pouch
leather to cover the entire valve block. The leather then serves as a gasket as well
as a cut out valve assembly. There are enough screws in these that they will seal
very well this way provided you made sure everything is trued up well.
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28) The pouch leather has been sealed with Dow 111 and all
the nipples (which had been removed and polished) have been sealed back into the block
with a bead of burnt shellac.
29) The mounting bracket has been polished and screwed back onto the expression cut
out block using burnt shellac as a glue to reinforce the connection between the metal
bracket and the wood block.
30) This control valve assembly signals the theme pouches in the expression system
as well as actuating the hammer lift pneumatic which is attached to the action right
behind the spool box.