What are Vertical Gravity Separators?

Cleanawater on 2 June 2015

Industries such as manufacturing, mining, automotive, oil and gas produce large amounts of oily water. If this water is discarded without any treatment, it eventually joins rivers and oceans and is a serious threat to animals and vegetation.

A large scale example of the toxicity of oil is the 2010 Gulf of Mexico oil spill. Over the course of this disaster 11 people and over 750 animals were killed, and criminal charges and fines were laid for those found responsible.

Water Regulatory Authorities determine how businesses are allowed to release trade waste water into local sewerage. For example, a business located in Geelong is subject to the regulation imposed by Barwon Water, whilst a business in Box Hill is subject to Yarra Valley water regulations.

cleanawater vgs range

To treat oily water in accordance to these regulations, an oil water separator is necessary. A cheap and efficient way to treat oily water and ensure your business is following the law is a Vertical Gravity Separator (VGS).

A VGS oil separator works by forcing the oil in water to collect and form bigger droplets. These oil droplets will then float to the top of the tank to be separated.

Benefits for Australian Business

A VGS is a cost effective, compact and efficient solution to water and oil separation.

  • Avoid costly oily water disposal fees
  • Reuse water and save money by combining with a Cleanawater recycling system
  • Ensure environmentally friendly disposal of oily water
  • Compact and cost effective
  • Easy to install, run and maintain
  • Can be customised to suit flow rates of up to 3000 litres per hour

Find out more about Cleanawater's Oil Separator systems.

Business Applications and Solutions

Example 1: Manufacturing Compliance

A medium sized workshop produces oily water during the daily wash down of vehicles and equipment. The business is looking for a Water Authority compliant system that is small, low cost and low maintenance.


Cleanawater's VGS separator is ideal as it is compact, cost effective, low maintenance and ensures the business is treating oily water in accordance with the local Water Authority's regulation.

 cleaning industrial equipment2

Example 2: Industrial water treatment and recycling

A refueling facility regularly produces oily water and is unsure how to properly dispose of this water. The facility wants to ensure Water Authority compliance but has limited space to install the separator. They would also like to reuse this water to wash down trucks and equipment to reduce their mains water costs.


A VGS oil water separator combined with a water recycling system is an ideal solution for this business. The VGS will separate the oil, then the treated water will flow to the water recycling system so it can be reused for the wash-down bay.

How VGS oil separators work

Key Features

  • Capable of handling up to 3000 L/hour
  • Filtering SPAK material can be changed according to requirements
  • Ideal for small spaces and automatic operation
  • Water Authority compliant
  • Solutions can include non-emulsifying pumps, high quality stainless steel equipment, controllers and float switches


A VGS accelerates the naturally occurring separation of oil and sediments from water. When untreated water settles in a tank, oil will float to the top and solids will sink to the bottom.

VGS oil separators speed up this natural process by providing a large surface area where oil droplets can join together and form larger droplets. These larger oil droplets form layers of oil that easily float to the top of the tank making the separation process faster and more effective.

A VGS forces the formation of larger oil droplets using a series of cones inside the tank. These cones are made of a material that actively attracts oil droplets and provide a surface for oil droplets to merge.

This process increases the speed of separating oil and water, as well as allowing a constant flow of oily water to be treated.

A Technical Guide to VGS operation

tall oil water separator vgs

Entering the tank

The way oily water is fed into the tank is crucial for the successful operation of a VGS. When oily water is pumped using a high speed pump such as centrifugal or submersible pumps, emulsification can occur. As the pump moves water at high speeds, it disrupts the chemical bond of oil and water particles, which can lead to the two mixing and becoming an emulsion.

An oil and water emulsion is difficult to separate therefore an appropriate low speed pump must be used. These are known as non-emulsifying pumps. Non-emulsifying pumps gently transport water without creating turbulence or excessively disrupting the fluid.

Two of the most cost effective non-emulsifying pumps are Diaphragm pumps and Progressive Cavity Pumps. These pumps operate at low speed and are able to handle thick fluids and large solid sediment in the fluid.

oil water separation

Oil and water separation

Fast and adequate oil and water separation is possible thanks to a truncated conical spiral pack (SPAK). A SPAK is a series of filtering cones along the tank that provide a surface where oil can adhere, and water is forced to cascade down the tank.

The SPAK is made out of polypropylene material (PP) which has oleophilic, or ‘oil attracting’, properties. The conical shape of the SPAK provides the largest surface area possible for oil droplets to combine. The larger the oil droplets, the faster they will float to the top of the tank.

Oily water enters the VGS through a bottom inlet leg and flows to the top of the tank. As oily water is released into the tank, the SPAK begins to attract oil. For water to sink to the bottom of the tank, it must travel down the slope of the cones and cascade down onto the next filter.

This forced movement down the gradient of the filter allows small and less buoyant oil droplets a chance to adhere to the cones. If the surface area of the filtering mean was smaller, these small droplets would be carried away with “clean” water, resulting in a higher concentration of oil in the treated water.

Exiting the tank

vgs sludge

Sediment particles that are heavier than water will sink to the bottom of the tank and form sludge that can be easily drained through an outlet pipe.

Clean water is discharged through a hose located slightly below half way of the tank and oil exits from the top of the oil water separator tank.



A VGS is a compact and efficient solution to oil water separation for industrial and commercial applications.

Water treated by a VGS is Water Authority compliant and can be safely discharged to a sewer, leach drain or in some circumstances, to stormwater.

VGSs are a fantastic technology to reduce costly water disposal fees. VGSs can also combine with other Cleanawater systems so that treated water can be recycled for irrigation, wash down bays, or used as an alternative to mains water.

Cleanawater offers highly technical expertise, excellent quality equipment and a personalised approach to your business' needs.

Ensure your business is water compliant and drastically reduce business costs by implementing a water treatment system.

Call Cleanawater on 1800 353 788 to discuss how to get your business water authority compliant and reduce your water disposal fees.

Further reading