MIL-DTL-23953 Valves, Combined Vent-Check, For Submarine Mbt Blow Lines \(Sizes 2.00 And 2.50 Inches\)This specification covers the construction, testing, and operation of combined vent-check valves with a nominal pressure seating of 4,500 pounds per square inch gage \(psig\), for use in submarine main ballast tank \(MBT\) high-pressure air blow lines \(sizes 2.00 and 2.50 inches\).