What is the best pump to use with an oil water separator?

Cleanawater on 27 June 2018

The performance of oil water separators can be severely compromised by a turbulent inlet flow. Pumps move liquid product along pipes from a holding tank to an oil water separator. During this process, the problem is that some pumps create a lot of mixing of the liquid, while others cause less churning by their action. When dealing with oil separators, the more the wastewater is agitated by pumping, the less effective the separator will be.

Agitating water containing oil causes the oil to break down into tiny droplets or to even form an emulsion. In these worst-case conditions, the oil cannot be separated from the water using a separator at all. The right pump causes a smooth flow of liquid into the oil water separator leaving the oil droplets as large as possible to enable easy separation.

So, what are the best types of oil water separator pumps?

Types of pumps

Pump typeCharacteristicsSuitable for Oil Water Separators?

Diaphragm

The diaphragm draws water into a chamber through an inlet valve then pushes it out through a discharge valve.

Very suitable due to limited agitation.

Helical Rotor

A helical rotor pump acts like a large screw. It pushes water along the thread from the suction to the discharge.

Very suitable due to limited agitation.

Submersible pumps

A submersible pump has a spinning rotor which looks like a fan blade. It sucks water up as it spins and then discharges it.

Very poor. Submersible pumps cut through the water, agitating the oil water mixture.

Pressure Pumps

Also known as centrifugal pumps, their veined impeller draws water in on the suction side and discharges it at a higher pressure.

Poor. Veined impellers cut through water agitating the oil water mixture.

How does a pump integrate with an oil water separator?

When selecting a pump for your oil water separator system, it is important to size the pump correctly. Sizing is based on the volume of water to be pumped, the distance between the holding tank and the separator, as well as differences in height (known as head) in the system. Even with a low agitation pump, a mismatch in sizing could cause turbulence in the water stream.

Pumps are normally automatically started and stopped using float switches in the holding tank. A build-up of sludge in the tank could cause the float switch to get stuck, thus affecting the pump performance. Automated systems can be configured with alarms to alert operators about problems with the system.

Running a pump dry is never recommended, although some pumps are better suited to handle these conditions than others. Dry-running will eventually shorten the pump's life and could result in seal leaks, which may spread into the environment. Some wastewater systems are specified with standby pumps to ensure that the system keeps working even if a pump fails.

If there is a large volume of oil in the trade waste, it may be necessary to use a floating skimmer in the tank as a first step before pumping the trade waste through an oil water separator. If the separator is far removed from the discharge sewer, a separate pump may be required to transfer the treated water. Agitation is not a major issue for the treated water because the oil has already been removed.

Maintaining a pump

oil water separator pumps

Diaphragm pumps are easy to maintain. The high wearing part is the diaphragm itself, which can be changed out in a simple maintenance procedure. This is an advantage due to the minimum downtime required to perform the task.

Helical rotor pumps have rotors and stators, which can wear due to abrasion. Once they are worn, they must be replaced, which is normally quite costly. For this reason, helical rotor pumps may not be suitable for trade waste streams containing solids. It is also important not to run these pumps dry because the liquid helps lubricate the seal between the rotor and the stator to prevent damage and leaks.

Contact us to talk about oil water separator pumps

Cleanawater has more than 20 years experience in trade waste systems including oil water separators. Our experts can help you design your separator system including tanks and pumps in order to ensure optimum performance and minimum interruption. We also provide maintenance and servicing to help keep your system running as per design.

Find out more at Cleanawater or call our expert team on 1800 353 788 today to arrange a consultation for your oil water separator and pump needs.