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MMD > Archives > September 2001 > 2001.09.12 > 09Prev  Next


Duo-Art Cam-Operated Steamboat Pump
By Craig Brougher

One observation about the Duo-Art "Steamboat" pump thread that is
interesting, and something I had not read anywhere else, is how they
vary.  The main way that the pump itself varies is in the number of
flap valves (exhausters) used.  The earliest ones had 72 (count 'em)
flaps, all told.  That was 6 intake and 6 exhaust flaps in each of
the 6 bellows.

Later ones, but just as quiet, had 36 flap valves, or 3 and 3.  The
inside flaps all use leather flap seats.  I can't say that they had
models that didn't use leather seats all around, either, but I haven't
yet run into those.

That's a minimum of 108 leather strips for the old pump and 54 strips
for the later model.  It takes about two full skins of leather just to
recover them.

The bellows are poplar wood and the two halves are glued together
without gaskets after their full assembly.  These have to be ripped
apart to restore, and it's a cinch that many of these components will
have to be extensively repaired or remanufactured.  This is a very
difficult pump to restore completely, and I don't recommend it to
novices.  It's quiet, yes, but it has a ridiculous amount of overkill
bordering on the obscene.

The reason they are quiet is because they reciprocate so slowly.
However, one of the things that break down on these pumps is the
leather covered rollers sprung against the cast iron cams.  And when
these are rebuilt, you then understand the magnitude of the true
differences between leather tanned for industrial purposes, and leather
tanned for clothing.

You might not be able to look and tell the difference, but just skive
and taper, then wet, stretch, and glue new leather around those
rollers, and when they are completely dry again, see how long they last
under constant playing.  Those strips have to be tapered for an overlap
of about 3/4" to 1".  I recommend buckskin or heavy kangaroo leather.
But none of it is as good as the leather that was originally used,
because industrial leather is prestretched and staked during the
tanning process to permanently compress the collagen.

One last thing about these pumps is their pulley arrangement.  This
also changed with time.  You don't need 3 or 4 parallel belts anymore,
unless you want them.  But the old systems had 4/2 slot pot metal
pulleys; these must be replaced with iron.  Boston Gear sells the right
ones.

Today, with composition V-belt drives, it isn't necessary to use a
4-belt system because composition belting is far stronger and longer
lasting than leather, and you can't buy leather belts at all today.
So here is where I'd definitely make a change if you have to replace
a pot metal pulley.

You might notice that the bearings in this pump are graphite greased
wood with a pinch screw and oiling cups.  If there is any wear, notice
that most of the noticeable wear is in the shaft, rather than the
bearing -- just like in the old steamships.

One last comment is that after the bellows are returned to the manifold
and reglued, to remove them again will again destroy the pump and its
parts.  You will have to make new parts and maybe a new manifold.  So
you want to make sure that the bellows are flawless and that all flaps
seat perfectly before reassembly.  Do not expect the vacuum to seat
your flaps.  There are too many of them.

And the rollers have to contact the cams absolutely square.  That
means, you may have to shim to get this squareness, after you "clamp"
the roller to the cam to establish square.  Do not use paper.  Only
use veneer.

Also, the bellows cannot be reglued back to a gasket so that removal
will be easier, for two reasons.  First, there is a tremendous amount
of force required to open these pumps against the pressure of the air,
particularly when the Duo-Art is calling for maximum pressure.  That's
about 3-1/4 pounds per square inch of force divided by the lever length
to the center of the bellows.  An enormous amount of force!  And since
there is no place to put screws or bolts without seriously modifying
the design, how else are you going to test the pump the first time but
to glue it all up first?

These pumps, when restored completely, will test the best rebuilder.
It's just that I have never run into any others yet that have been
totally restored except my own, so I feel that there are many
rebuilders out there who have yet to do one all the way through.
Otherwise, we would have heard all about these things by now.  The
moaning and the groaning, you know?

It isn't too hard to recover one.  That's just a minor repair, not a
restoration.  But 72 or 36 flaps, half of which must hold the vacuum
and which are almost 100 years old including their seats, will not
last very long.

As far as quiet running, when the piano has been closed up, a good old
rotary pump that's been rebuilt is just about as quiet as these things
ever were, and it's unnecessary to try to get more quiet.  The keys
and the pedals themselves are noisier than either pump.

I really don't see any advantage to the steamboat pumps, except they
increase the work, hence the cost, of a reproducer by at least half
again as much.  They are an enormous amount of work, and no longer are
you going to get away with ignoring its inside flap valves, entombed
in a poplar wood.  Also, just because you have completely restored it
doesn't mean it won't develop a problem.  If it's the model with 72
flap valves, then what are your chances?  Until you've done one
completely, you have no idea of what you are in for.  Forewarned is
forearmed.

Craig Brougher


(Message sent Wed 12 Sep 2001, 14:17:16 GMT, from time zone GMT-0700.)

Key Words in Subject:  Cam-Operated, Duo-Art, Pump, Steamboat

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