Principle Oily water is pumped through a non-return valve in the inlet to the separator; It enters the outer annular space and flows vertically upwards towards the primary collection zone where the larger globules of oil, which separate easily by gravity, collect The water then flows downwards through the inner annular space into the bottom of the separator, through ports into the coalescing bed at a very low speed when the oil adheres to the granular material in the bed and forms, in effect, a climbing film which moves upwards through the bed at a slower speed than the water The top of the bed is covered by a perforated plate. When the oil reaches the underside of this plate it flows through the perforations and due to its viscosity and surface tension, begins to form globules which increase in size until they have sufficient buoyancy to float upwards at a faster rate than the water and collect in the secondary zone while the water flows through the water screen and into the outlet pipePrinciple • Oily water is pumped through a non-return valve in the inlet to the separator; it enters the outer annular space and flows vertically upwards towards the primary collection zone where the larger globules of oil, which separate easily by gravity, collect. • The water then flows downwards through the inner annular space into the bottom of the separator, through ports into the coalescing bed at a very low speed when the oil adheres to the granular material in the bed and forms, in effect, a climbing film which moves upwards through the bed at a slower speed than the water. • The top of the bed is covered by a perforated plate. When the oil reaches the underside of this plate it flows through the perforations and due to its viscosity and surface tension, begins to form globules which increase in size until they have sufficient buoyancy to float upwards at a faster rate than the water and collect in the secondary zone while the water flows through the water screen and into the outlet pipe