A gate valve (11) includes a body with a flow passage (17, 19) intersected by a gate cavity (15) and a gate (21) with an axis (20), the gate being axially movable in the gate cavity between a gate closed position and a gate open position. A lifting device (25) is in engagement with a stem (34) of the gate to move the gate to the gate open position. A port (57) extends from a first external surface (29) of the gate to a second external surface(53) of the gate. A seal member (59) is mechanically connected to the lifting device, the seal member being moveable in response to axial movement of the lifting device between a seal open position where fluids can flow through the port and a seal closed position where the seal member blocks fluids from flowing through the port.