The term “trunnion-mounted” describes a ball valve design where the ball is fixed in the plane of the axis of rotation and where the seats are free to move laterally towards the ball sealing surface to effect a leak tight seal. The movement of the seats is by a combination of flow forces, of pressure loads and of other mechanical loads such as springs or similar mechanism. The load exerted by the thrust spring or similar mechanism at the seats provides the sealing loads to effect the seat to ball sealing at low pressare conditions. The loading at the seat to ball interface is assisted by pressure loading as the line pressure increases. The bearings at each trunnion and the sizing of the stem shaft diameters are designed to withstand operational and pressare loads as specified by application, pressure class, differential pressure conditions and as may be required for the gear or motor operation of the valve.