Using compressed air through a venturi pump to suck oil?

[kunalv]

Hello, was wondering if I could pass compressed air through a venturi pump to pull floating oil from a tank? If yes, how do I control the eventual mixing of oil with the air from the outlet end?

The requirement is given to me by one of my clients who wants an easy, and low-cost solution to remove 'tramp' oil from their CNC machine coolant tanks. I've drawn a quick sketch to explain the application. Can this work? I am assuming the oil will mix with the air inside the venturi to form a kind of mist?

Any advice would be great. Thanks.

 

[Baluncore]

I expect the venturi will produce a hydroxide foam or sludge.

What type of coolant is used?
What is the source and type of oil you want to remove?

 

[kunalv]

I expect the venturi will produce a hydroxide foam or sludge.

What type of coolant is used?
What is the source and type of oil you want to remove?

Type of coolant : water-soluble cutting oils.

Source & Type of Oil : Tramp oil is a term that describes any unwanted hydrocarbon-based substance that contaminates machine coolant. This can be hydraulic oils from slideways in the machine or any other sources within the machine.

 

[Lnewqban]

Type of coolant : water-soluble cutting oils.

Welcome!
In that case, why the oil and water separation shown in the tank of your diagram?
Why not to use the built-in coolant pump of the machines?
The height at which you can lift with a ventury is limited.

 

[Baluncore]

Type of coolant : water-soluble cutting oils.
Source & Type of Oil : Tramp oil is a term that describes any unwanted hydrocarbon-based substance that contaminates machine coolant. This can be hydraulic oils from slideways in the machine or any other sources within the machine.

The ratio of water to soluble oil will be about 20:1. That forms a milky emulsion with a high density, that will wet and cool the cutter, and the surface of the material being cut. Slideway oil and some hydraulic oils are hydrophobic, with a lower density than water, so they float on the surface of the water based cutting fluid. I do wonder why removal of the tramp oil is necessary, so long as it remains separated on the surface, and the cutting fluid is drawn from below.

I have removed oil films from water by dropping a paper kitchen towel onto the surface. The oil is absorbed into the paper as the paper sinks into the surface, but floats on the water. Then I slide off the paper towel and dispose of it. For thicker oil I have thrown fine sawdust onto the surface, waited for a few minutes, then used a mesh strainer to remove the sawdust floating just below the surface with the attached oil.

I expect a surface skimmer of some type will be required to remove the surface oil film.
There are a couple of reasons why I would avoid using a pump to remove the surface oil.
Firstly; the pH of cutting fluid will probably be above 9. Energetic mixing of cutting fluid with the hydrophobic oil may produce hydroxides or soap in that environment.
Secondly; the oil will need to be localised before it is lifted. That might be done by floating an inverted funnel in the surface of the fluid. Tramp oil would rise, and move towards the rising neck of the funnel, from where it can be extracted.

 

[jrmichler]

I am assuming the oil will mix with the air inside the venturi to form a kind of mist?

This will definitely happen. If you still want to explore the venturi approach, search mist eliminator for ways to deal with the mist.