response to as a function of the measured breakout torque and or measured running torque when indexing the rotary valve the seating pressure may therefore be controlled in real time throughout the valve indexing in response to one or both of these torques according to a particular embodiment control of the seating or dome pressure is possible using a back pressure regulating device on a sealant fluid outlet from the dome on the first side of the seal sheet for example the side adjacent the rotor or rotor plate the seating or dome pressure is often controlled using a control system that maintains at least a minimum seating pressure the differential pressure across the seal sheet is the difference between the seating or dome pressure and the countering pressure exerted on the second side of the seal sheet for example from the stationary track plate of the stator the track plate is therefore typically on a second side of the seal sheet opposite the first side on which the seating pressure is controlled in order to ensure that a positive sealing force generally the seating pressure minus the track plate pressure is exhibited by the seal sheet onto the track plate the minimum seating pressure as a control setpoint is typically from about 2 psig 0 14 kg cm2 to about 20 psig 0 28 kg.