What would cause the material to back up in the controls, clog the moisture trap, and sometimes cause the pop-up to stick up?
When the blast pot is connected to a common air supply source upstream demand can drop the supply pressure resulting in reverse differential pressure. The higher pressure at the blast pot will back flow air to balance the pressure. The back flow will carry abrasive resulting in contamination of moisture separator and controls.
In pressure hold systems (TV) venting the compressed air at the source in lieu of shutting the blast pot inlet ball valve and depressurizing locally will result in back flow.
In back flow conditions abrasive is carried into the blast pot internal popup piping. The abrasive in the piping will jam the popup and not allow it to drop when the blast pot is depressurized.
