It's not a non-return valve per say, rather a check valve or pressure relief valve. If the oil filter becomes clogged, the oil pump will keep pumping pressurised oil through it. If the filter doesn't have a valve fitted, the pressure can't vent.
__________________
1996 850 T5 - Sold
2003 S40 1.9d - Sold
2004 S60 D5
|