The control of the oil tension while in the lock-up clutch is completed via two valves: the relay valve and the sign valve. In this kind of arrangement the signal valve controls the force on 1 side of the relay valve, which controls the tension while in the lock-up clutch. https://torqueconverterclutch19528.dm-blog.com/34268485/torque-converter-clutch-no-further-a-mystery