Abstract: A seal for use in a cylindrical groove in a cylindrical item positioned in a cylinder such as a rotary valve where the seal is subjected to reciprocating forces as the item and the cylinder rotate with respect to each other. The seal has two adjacent pairs of outer sealing rings with each pair being backed up by a pair of backup rings which are positioned to bear outwardly on the sealing rings. A spring is positioned to push the pairs of sealing rings and the associated backup rings to the opposite sides of the groove to form the side seals and hydraulic pressure is provided underneath the rings to urge them outwardly to form the outward seal.