Slab Gate Valves also named "Through Conduit Gate Valves" are very useful in transportation pipe lines for gas, crude oil and oil products.
The through conduit gate valve is designed and manufactured with a rising spindle for the floating motion of the valve. During operation, the pipe fluid fills the bore cavity. The fluid pressure in the bore cavity generates a vertical force on the stem that pushes the trim from bottom to top. In an emergency, this force is used to help the actuator spring to bring the valve door into the required failure mode position.
The standard operating design means that the valve is closed with the valve stem down and is common for a fail open configuration because the "stem ejection force" helps the actuator spring to open the valve.
The reverse operating design means that the valve is closed with the valve stem up and is common for a fail close configuration, because the "stem ejection force" helps the actuator spring to close the valve.
Slab valve construction includes spring-loaded floating seats that provide positive seating on both sides regardless of upstream or downstream pressure conditions.
The seat seals are spring loaded to ensure sealing under low pressure. As line pressure increases, the contact pressure between the seat and port increases accordingly for a positive seal. Since both seats are separately energized by the pressure differential across the seat itself, the valve cavity can be vented when the upstream and/or downstream side is pressurized.
The valve exhibits identical performance regardless of flow direction and/or direction of pressure differential. Several solutions are available for seat-to-body gaskets, depending on the type of operating fluid, pressure and temperature.