A valve employing a coupling disk to rotate the valve member so that rotative force is applied to the valve member in a direction away from the seat during opening of the valve and/or in a direction toward the seat during closing of the valve. Closing force is provided by a spring in a dome chamber and a gas charge in the dome chamber. A float valve controls fluid entry into the dome chamber to trap the gas charge therein while permitting the introduction of liquid from a balance-closure assist line to increase the pressure of the gas charge and assist in closing the valve member.