The design of the Dresser Style 175 Gas Service Valve utilizes two complementary sealing principles working together to assure a positive shut-off at all rated working pressures up to 150 psig. The oil-tempered steel spring exerts a constant force on the tapered plug and seal inserts, providing a seal against low line pressure. At higher pressures, this spring load is supplemented through a unique design, which employs line pressure to exert an additional positive sealing force. As line pressure is increased, greater sealing force on the elastomeric seals is produced causing the valve to remain gas tight at all working pressures within its recommended working range.