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"Tips and Tricks"

Understanding the Pouch in a Player Piano


Reference Materials

   Ian noticed these felt washers in one of the devices he's rebuilding and wanted to know why they were there. However, prior to asking me about them, he decided to replace the valve facings and leave out the waskers. He found that the device worked without them, which prompted him to write to me. Here's what he said:

   On a couple of these smaller valve boxes (for the Theme boost, and cutout boost as well), there are primary poppets that had cloth washers between the bottom facing and bottom of valve (picture). These cloth washers were not present in the motor box or general primary chest, but these little valve boxes are laid out in a slightly different way - they have a larger internal cavity, which means there is more gap between the bottom of the poppet and the pouch. So I am wondering about the need to keep the washers, if they will make an important difference in reaction time with the pouch. I tested one box with new facings, but no cloth washers, they still do seem to work, but...maybe something I am not considering?

   Here is my reply.

   I feel like I've probably said this before.... "Replicate the original"!

   There have been perhaps hundreds of times in my career when I didn't fully understand why the manufacturer did something. There are still times when I scratch my head and say to myself, 'Why did they do that'? Regardless of what I may or may not know, I have never assumed that I was smarter than the people who designed and built these machines. On occasion, I've encountered cheaply made units, and in such cases I will try to make improvements if I can prove that my way is superior to the original.

   In this particular instance, the answer to your question is fairly obvious. The felt washers are spacers. I don't want to get into the theory of operation of a pouch, but all you need to look at are the numerous pictures of the orientation of the pouch and the valve button to see that during normal operation, the pouch will rarely (if ever) extend beyond the level of the wood onto which the pouch is mounted. There's a reason for that. Primarily, it has to do with the natural tendency of the leather to hold its shape. Ideally, the pouch will always have a concave shape. That way, it has a natural tendency to return to the concave position when the atmosphere that causes it to inflate is gone.

   You have to remember that the pouch NEVER gets 'sucked' back to the 'down' position. NEVER! Once the atmosphere that inflates the pouch is gone, there's an equal amount (level) of vacuum on both sides of the pouch. So, what's going to happen? The answer is NOTHING! There is no 'applied force' working on the membrane to cause it to move in any particular direction. So, why does the pouch want to return to the 'down' (or concave) position? It's because of the natural tendency of the leather to return to its former (or at rest) position. If that position isn't positively concave, the leather will have a tendency to hold the valve 'up' or open. While this might not be a problem with new leather that doesn't yet have a memory (or a set), it will, over time, become a problem.

   Lastly, have you ever asked yourself, "Why is it important to 'dish' the pouch?" Now you should have a clearer understanding of the reason.

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This page was last revised July 12, 2017 by John A. Tuttle, who Assumes No Liability
For The Accuracy or Validity of the Statements and/or Opinions
Expressed within the Pages of the Player-Care Domain.
Cartoon Graphics by E7 Style Graphics (Eric Styles)


Since "Player-Care" is an internet business, I prefer that we correspond via E-Mail (click here to fill out the 'Request Form'). However, if I'm not in the middle of some other activity, you can reach me at 732-840-8787. But please understand that during the hours from 8AM-5PM EST (Mon-Sat), I'm generally quite busy. So, I probably won't answer the phone. If you get the answering machine, please leave a detailed message stating the reason for your call. Also, repeat your name and phone number clearly and distinctly. By necessity, I prioritize everything in my life. And, if you call and just leave your name and number, and ask me to call you back, it might be a day or two before I return your call. Why? Because I don't know why you want me to call and I might not be prepared to assist you in an effective and efficient manner. If you leave me an E-Mail address (which I prefer), spell it out phonetically. The more you do to help me, the more I can help you in return. Don't rush. You have four minutes to record your message.



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