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.