The control of the oil strain in the lock-up clutch is completed through two valves: the relay valve as well as signal valve. In this type of arrangement the sign valve controls the force on just one side on the relay valve, which controls the force within the lock-up clutch. https://lukashtvww.blogminds.com/the-smart-trick-of-torque-converter-clutch-that-nobody-is-discussing-31383684