Abstract: A sliding gate valve mechanism for use in teeming molten metal is provided with apparatus for accurately setting seal pressure between the valve plates and for adjusting the seal pressure during periods of valve operation. The invention enables such adjustments to be made to rectify malfunctions in valve operation without need to terminate teeming and to dismantle the valve mechanism. The invention is particularly advantageous in that the role played by mechanical springs in imparting valve seal pressure is relegated to secondary importance as leakage of molten metal between the plates can be terminated regardless of the operability of the springs.