CPI is one kind of high efficient oil-water gravity separator, now is widely used in oily wastewater treatment to remove bulk oil from water.

Gravity separation is the most straightforward method of wastewater treatment and is, therefore, utilized widely in industry for separation of settling and/or floatable impurities from a carrier liquid.

An enlarged separating surface can be achieved by placing various smaller planes on top of each other in the tank. If these planes are subsequently inclined in a tilted position, material separated between the plates is removed by the gravitational force. This is the principle on which the CPI corrugated plate pack is based.