Shear valve includes a hollow valve body having inlet and outlet flow passages thereto, a flat faced seal plate at the inner end of each flow passage having a port therethrough communicating with the flow passage and a closure comprising stem means reciprocable in the valve body transversely to the flow passage axes, a cage carried by the stem means having a bearing opening extending therethrough, the axis of the bearing opening being generally parallel to the axes of the flow passages, and a pair of seals in the form of flat end faced tubes reciprocably coaxially mounted in the cage in sealing relationship therewith and spring and fluid pressure biased apart into sealing engagement with the flat faces of the seal plates. Improvement according to the invention includes means mounting the cage to be rockable relative to the stem means to allow the seals to lie flat against the seal plates and sealingly engage therewith. Three forms of rockable mounting are disclosed, i.e. double tapered support opening in a spool type stem means, elastomer Oring mounting cage in support opening of a spool type stem means, and a stem means comprising two coaxial rods rockably engaging diametrically opposed sockets in the cage.