How it works: Oil filter

Date:29 November 2012 Tags:, ,

Clean oil is essential for a healthy engine, making the oil filter an indispensable organ. Here we explore the various parts of  Fram Extra Guard oil filter intended for cars and trucks. By Andrew Del-Colle

1. Tapping plate

This serves as the entry and exit point for oil. Small holes around the edge facilitate the free flow of oil into the container. The threaded centre hole is where the oil flows out and also how the container attaches to the engine.

2. Aanti-drainback valve

Because the oil filter is typically located towards the middle or bottom of an engine, this rubber valve has a flap that blocks oil from draining back into the fi lter when the engine is off.

3. Filter medium

The porous filter medium consists primarily of microscopic cellulose fibres along with synthetic fibres such as glass and polyester, which increase filtering efficiency and durability. The medium is also saturated with resin to give it strength and stiffness. Higher-grade filters have more synthetic fibres.

4. Pleats

Folding the filter medium creates a greater total surface area. The number of pleats depends on the medium’s thickness.

5. Centre steel tube

The centre tube provides structure and lets filtered oil return to the engine. The number, size and position of the holes is key to ensuring that the oil flow is not restricted.

6. Relief valve

On a cold start-up, oil can be too thick to filter. To prevent the engine from starving, the relief valve opens when the pressure builds enough to force the calibrated spring downward, allowing unfiltered oil into the centre tube through the top.

7. End disc

To keep unfiltered oil from leaking into the centre tube, a fibre or metal end disc is bonded to each end of the filter medium. Some brands forgo discs and use a sealant to create solid ends.

8. Retainer

A thin bit of metal that acts as a leaf spring, the retainer keeps the filter medium and end disc tight against the tapping plate.

Gary Bilski, chief engineer at Fram Group: “When a vehicle’s idling, the oil filter receives anything from 4 to 8 litres a minute, but at 4 000 to 5 000 r/min, the fl ow can hit 20 to 40 litres.”

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