Neway parallel slide gate valves are designed with positional seal, using the line pressure as a sealing force. The compressed spring between the two closure members provides an initial seal during low pressure conditions. The increasing line pressure will push the closure members with higer forces aginst each other which creates the primary seal. The higher the medium pressure, the better the sealing performance. Therefore this valve type is widely used in high pressure and high temperature services such as steam and feedwater.