How coalescing removes tramp oils from spent fluid | PRAB
PRAB > News & Knowledge > Blog > Coalescing for the effective removal of tramp oils from spent fluid

Coalescing for the effective removal of tramp oils from spent fluid

Tramp Oils Coalescing in Water

Tramp oil that floats on the surface of water based cutting fluid in the machine sump is problematic in a variety of ways. Separating and removing this oil should be a priority to eliminate its negative effects and maximize coolant effectiveness. By removing tramp oil from the sump with a fluid recycling system, metalworking operations can cut costs and reap many other benefits including the following:

Reduce or Eliminate


Removing tramp oils can be done using many different processes. However, the most effective method is coalescing. As part of the metalworking fluid recycling process, coalescing is a technique used to remove free-floating and mechanically dispersed tramp oils from spent cutting fluid using coalescing media. This media, located inside the recycling unit, attracts small droplets of oil until they come together (coalesce) forming larger droplets. Those drops rise to the next droplet and the droplet becomes even larger, rising to the top of a separator where they are removed by oil weirs.

Media basket full of tellerettes and pall rings
Media basket full of tellerettes and pall rings inside the Cross Flow Separator, the smallest model tramp oil separator.
Tramp oil separator full of spent fluid
Tramp oil separator at work with bubbling for airsparging

When choosing the right coalescing system for the shop floor, there are differences in efficiency and time savings depending on the supplier, but for the most part many suppliers offer both machine side and centralized systems. Here are just a few of things to look at when choosing a coalescer (fluid recycling system):

  • What type of media is used?
  • What type of maintenance will the system require?
  • Is the system self-cleaning?
  • Is the system proven to be efficient at other metalworking operations?
  • What is the proven payback time on the system?

PRAB’s Guardian™ Coolant Recycling System and Tramp Oil Separator use unique tellerettes and pall rings as the coalescing media which are in a media basket in a compartment of their filtration systems. The media in the Guardian and tramp oil separator is automatically cleaned daily using air sparging to eliminate manual cleaning—significantly reducing maintenance labor. In air sparging, small air bubbles are released under the media basket to scrub it clean and remove any oil-soaked solids that may have collected on the media.

Air Sparging Diagram
In air sparging, small air bubbles are released under the media basket—cleaning the media and removing any oil-soaked solids
Guardian with Bubbles from Air Sparging
PRAB Centralized Guardian Coolant Recycling System at work

Unlike PRAB, some fluid recycling equipment suppliers use stainless steel plates (coalescing plate packs) or other types of coalescing media which have a lower affinity for oil and therefore are not as efficient. They may claim that steel plates will not plug like PRAB’s media coalescers. However, a wide spacing is put between the plates to prevent plugging and that wide space allows larger oil droplets to pass between the plates which are then carried over into the coolant—decreasing efficiency. In addition, when the plate pack becomes plugged with solids they must be manually removed and cleaned. Because PRAB’s media is automatically self-cleaning daily, it eliminates the need to remove and manually clean the coalescing media.

To talk with a PRAB Fluid Recycling Expert about a tramp oil removal solution for your plant, contact us today.