Non-return valve · Due to the valve operation, the camshaft

911 Engine 1 1_07_02 Non-return valve Due to the valve operation, the camshaft requires a high drive torque at times, at other times the camshaft runs independently (changer-over torque). If a non-return valve is operated in the P-line and the 4-way valve is energised (adjustment in advanced valve timing direction), the adjuster, with the camshaft running on, independently draws oil via the feed line, the 4-way proportioning valve and the non-return valve. If the camshaft then stays behind due to the high drive torque, the non-return valve closes and the oil 1_04_02 cannot escape. During this period, the cam- 1 - Adjustment direction, retardshaft is taken over the oil cushion by the 2 - Adjustment direction, advancechain sprockets, as when free-wheeling. The 3 - Camshaft adjusteradvancing and retarding of the camshaft 4 - 4-way valverepeats itself, so that the camshaft 5 - Non-return valveindependently moves progressively towards 6 - Oil pumpadvanced valve timing. As the above 7 - Oil sumpdescribed principle only functions on very leak-tight adjustment systems and low- friction valve gears, oil pressure is required. To avoid the necessity of an extremely large oil pump, the above described principle is exploited, with a hot engine and low engine speed i.e. with low oil pressure, through the use of the non-return valve. The non-return valve is used to increase the adjustment speed at low oil pressures. 2002 Service Information 1 - 11