Abstract: A moisture barrier seal for use on a hopper car hatch opening that does not need to be removed before vacuum unloading of the hopper car due to the use of a grained plastic such as vertically drawn or cast polyethylene which will rupture as soon as the seal is subjected to the pressure differential across the seal created by the application of vacuum to the hopper car. The moisture barrier layer when combined with a filter layer forms a combination moisture barrier and filter seal.

Abstract: A moisture barrier seal for use on a hopper car hatch opening that does not need to be removed before vacuum unloading of the hopper car due to the use of a grained plastic such as vertically drawn or cast polyethylene which will rupture as soon as the seal is subjected to the pressure differential across the seal created by the application of vacuum to the hopper car. The moisture barrier layer when combined with a filter layer forms a combination moisture barrier and filter seal.

Abstract: A system for preventing contamination of particulate material in a railroad hopper car during transportation and unloading of the material from the car, comprising transporting the material in the railroad hopper car with a filter on each of the various inlet and outlet openings of the car, then upon reaching the point for unloading, applying a vacuum to draw the material out of the car through one spout with its filter removed, while leaving the filters in place on the other openings in the car to prevent contamination of the product from external sources during transportation and unloading. The preferred filter for the railroad car spouts has a frame, a conical filter bag, and a filter bag support ring for mounting on a spout on the car.