Gum Rubber Compression.
In the past year, Milnor has started using gum rubber in lieu of water to fill the Single Stage Press diaphragm. As more knowledge of the behavior of the gum rubber has come to light, we now know that the gum rubber will compress over time and that at a certain point the user may have to add more rubber to the stack to properly fill the diaphragm. When the gum rubber stack height is less than the diaphragm side wall dimension, the sidewall and the heel of the diaphragm will take more pressure that the middle of the diaphragm. This added pressure will cause a side wall collapse. The force also may cause an excessive shearing force of the rubber that is bonded to the metal ring embedded in the diaphragm. This will try and force the rubber from the metal ring.

It is important to keep the diaphragm properly filled. An under-filled diaphragm will substantially shorten the diaphragm's life.