Vacuum demand flow valve

摘要

A valve is disclosed for dispensing a flowable material. The valve has a first chamber (40) at a first pressure wherein said first chamber (40) defines an outlet (28) in communication with said first chamber (40). A second chamber (42) is at a second pressure. The valve has a stop (18) indexed against a third pressure, operating to selectively place the first chamber (40) into communication with the second chamber (42). The stop (18) is operative to connect the second chamber (42) to said first chamber (40) when the first pressure is less than the third pressure. The valve includes a vent (520) for venting the second chamber (42) when flowable material is removed.