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MMD > Archives > May 1998 > 1998.05.26 > 08Prev  Next


Autopiano Secondary Valve Problem
By Sam Harris

Tonight I have a mess.  I'm restoring the secondary valves of an
Autopiano stack and I need some serious advice.  Here is a list of what
I have done.

01.  I have already replaced all pouches and sealed them with 50/50
     rubber cement.
02.  Replaced both valve facings.
03.  To keep adequate wobble I used a .016 feeler gage and tapped the
     force-fit collar tight then removed gage.
04.  Set valve travel to 1/16" per Reblitz book for valves with felt.
05.  Reinstalled the valves shellacking as I went.
06.  Adjusted the valve button clearance.
07.  Spring clamped the valve chest together and set vacuum at 7".
08.  Masked off input channels and clamped manifold to valve chest.
09.  Listened to all valves and there was NO leakage in the off position.
10.  Used the supply channel opposite manifold connection as a
     testing point and had 7".
11.  Set out to test each valve and trouble was found.
12.  Appears as though there is not ENOUGH valve travel.
13.  At 7" the valve operates and measures about 6"
14.  Some valves screech.
15.  When the pneumatic feed channel is blocked with my finger I can
     feel the valve turn on, but when I remove my finger the valve
     shuts off again.

It appears that the leather is being pulled to the inside seat.  When
the test was done at 12" vacuum the valves did not turn on at all until
I blocked the pneumatic feed channels with a finger.

Here are what I consider possible causes.

01.  Not enough valve travel.   Surely you do not need more that 1/16"
travel.  This is what the valves measured before any work

02.  Insufficient pouch depth.   Probably not because the atmosphere
side seats very well with no indication that more movement is needed,
and the pouches just touch bottom as did the originals.

03.  Too much wobble.   Action taken: disassembled 4 valves and used
a .010 feeler gage and tapped the collars tight then removed gage.
Results: No significant change.

04.  Too much clearance between pouch and valve button.   Action taken.
Tried to force the valve up by grasping stem and pulling.  No change in
vacuum test results.  The outside seats work great.  If there was too
much clearance making the throw short the outside valves would not seat
and nice as they do.

05.  Wrong type leather.   In my thinking I'm afraid this may be the
answer.  Although the leather measures the proper thickens it in no way
resembles the texture of the old valve leather which was somewhat
stiff.

This leather is not stiff at all.  It is very very pliable and in fact
this may be why I'm having problems because it appears that there is
not enough "stiffness" to the leather to allow it to be pulled away
from the inside seat, meaning that the pressure is forcing the limber
leather to bend around the metal backing plates and thus partially seal
off the supply to the pneumatics.

The leather used was the white valve leather supplied from "The Leather
House".  I am in no way blaming them here, they simply sent me what I
ordered.  I wish I had sent a sample of what I needed and let them
match it.  This leather is working fine for the atmosphere side but
apparently I need a stiffer grade for the inside facings.

What are your thoughts?  I am new at this and I really didn't know if
this was the texture the leather was originally, apparently not.  I am
not going to do a half way job on this piano.  I'm already late on the
return date but I'm not going to let it go until it is right.  Man,
I wish some of you were here in town so I could show this to you.

Also, since we are on the subject: Do any of you use a feeler gage
to keep consistent wobble and if you do, or if you were going to,
what thickness would you use?

_Very, very frustrated_

Sam Harris - Greenville, North Carolina
http://www.geocities.com/Heartland/Ranch/9374


(Message sent Tue 26 May 1998, 04:57:53 GMT, from time zone GMT-0400.)

Key Words in Subject:  Autopiano, Problem, Secondary, Valve

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