Importance of anti-drain back valve
The anti-drain back valve usually has the form of a rubber membrane adjacent to the inner side of the can type filter cover. The membrane covers the holes where the contaminated oil gets through to the filter and protects against the back flow after the engine stops. The anti-drain back valve reduces the duration time of the dry or semi-dry friction between the working parts of the engine because by preventing the oil flowing towards the oil pump it speeds up the oil stream getting to the working elements during the start of the engine, especially after a long stop. The application of the valve is conditioned by the position in which the filter has been screwed to the engine. If the filter is working in the „cover up” position, as shown in the picture below, the function of the valve is successfuly taken over by the gravitation. A valve is needed when the filter is screwed in from the side or from the top of the engine body.
Anti-drain back valve in the spin-on filter