“What is the benefit of using a coalescer over a mechanical skimmer?”
A mechanical skimmer only removes tramp oil and needs regular maintenance to keep chips and other debris off the pickup mechanism and scrapers.
The Muscle Coalescer, when dedicated to a sump, will constantly remove the oil layer and keep the coolant sump in circulation when the machine is idle, helping to prevent bacterial contamination which degrades coolant. Little to no maintenance is required, except filter bag replacement on chip filtering models. If floor space is at a premium near a machine, a mechanical skimmer may be a better option to remove tramp oil, then an Oxygenator whenever the pump does not run to help keep bacteria at bay.
“How do I know a coalescer will effectively separate tramp oil from my coolant?”
Coalescer efficiency is all about how long it holds the coolant versus how much oil gravity separates from the coolant within this time.
When new, most coolants will reject tramp oil within a matter of minutes. This is the best time to start using a coalescer, preventing emulsification of tramp oils. But to prevent waste, you can determine if a coalescer will work well on a used coolant batch. In a clear container, such as a water bottle, take a small sample of the fluid. Cap the bottle, shake it well, and then wait 15 minutes (for the Muscle). Whatever oils are rejected within this time are those that the coalescer will separate. Let the sample sit longer to see if there is oil that takes longer to separate. If there is additional oil, this sump should be changed as soon as practical since the coalescer will only recirculate oil back to the sump.
Note that high-pressure coolant delivery systems, such as for through-spindle coolant, cause tramp oil to deeply emulsify into coolant because of pressurization. During the separation test, you may see a separated layer that looks like a milkshake or sponge. This layer is made of lots of tramp oil, a bit of coolant, and tons of air bubbles, and is what you can expect as a tramp oil layer.