These valve performs an on/off or modulating function. Its name is derived from the flow-controlling ball valve located within the body of the valve. A hole through the center of the ball along one axis connects the inlet and outlet ports of the body. The ball itself is held in place by, and rotates 90º within, PTFE seats. These provide permanent lubrication, and keep the valve "bubble-tight." They are backed by elastomeric cushions, which provide pressure against the ball and, at the same time, compensate for wear. Elastomer O-rings are used for stem and carrier seals to prevent leakage to the atmosphere. In the open position, the flow is straight-through, and there is minimal pressure drop when the porting through the ball is the same size as the inside diameter of the pipe.