Back check valves allow flow in only one direction and are normally closed. They are installed in liquid filling connections on stationary storage tanks, bobtail delivery trucks, and liquid transfer lines. G100 Series are offered in two styles of seat construction: metal-to-metal or soft seat. The soft seated construction is for the filling connection on bobtail delivery trucks. Because the valve gives tight shutoff, piping on the bobtail can be depressurized for maintenance without leakage.