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MMD > Archives > June 1997 > 1997.06.06 > 08Prev  Next


Standard valve problem
By Craig Brougher

Sam Harris clarified his valve problem as two valves that only work at
low vacuum but not at high vacuum. There is only one thing that would
cause that-- When the primaries are mounted to the secondaries, those
two secondary valves, notes A and B-- are not actuated by their
primaries at higher vacuum.  Why? Because when those two primaries are
actuated, they do not send enough _air_ to their respective secondaries
to lift them at higher pressures.

This is one of those "iffy" situations that can be caused by a number of
marginal things.

   1) Too much play in the inside valve seat of the secondary valve.
      In other words, at low vacuum, it will work, but at high vacuum
      it "scoots" down the valve stem. So you have possibly too little
      valve travel and too much "flexibility" of the inside valve disk.

   2) Bad glueing of the secondary valve pouch. At low vacuum pressures,
      they are not stressed much so they stay sealed, but at high vacuum,
      they are stressed to stretch off the pouch board, and the resultant
      bleed leakage prevents the valve from operating. (my guess).

   3) Crazy things, caused by a comedy of errors, like what John Tuttle
      suggested-- Primaries that aren't lifting enough, plus secondary
      pouches that are sealed like cartridges will cause this.

Overall, you are dealing with marginal problems. If you have a leak
between the trackerbar and the primary, by which vacuum is allowed to
leak into the primary valve pouch, then when the vacuum is low, the
primary pops up and the secondary works. But when the vacuum is high,
the leak, which is a "flap" kind of leak (proportional) prevents the
primary from popping up, so the secondary doesn't work.

How to figure it out. Simple. Remove the player action to the bench and
watch the primary valve. Does it pop up? Check its next-door neighbor.
Given the same vacuum, does it pop up, too? Does it pop up as high? Is
it much higher?  What do you think about the lift of the primary valve?
(That can cause it, too).

Let's say that the primaries pass the test. Now you have isolated it to
either the channel to the secondaries, or the secondary valve. That won't
be hard to solve, after that.

Craig


(Message sent Fri 6 Jun 1997, 21:45:19 GMT, from time zone GMT.)

Key Words in Subject:  problem, Standard, valve

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