How can I avoid Foaming in my cutting fluid tank? (attached drawing for reference)

[kunalv]

Hi guys, facing a bit of a problem here. Please see the system layout here :


I've connected an eductor to the coolant pump in my machine. This eductor sucks the leaked cutting fluid from a tray underneath the machine I.e coolant passes through the venturi(let's call it motive) and returns to the tank and in this process a vacuum is developed which is used to suck up the oil from the tray which travels with the motive and enters my tank.

Now the problem I'm facing here is once all the leakage oil has been sucked up the device keeps sucking air which is then effectively injected into the coolant sump thereby causing a lot of foam.

How can I prevent air from entering the tank? I cannot use any timers or solenoids to turn off the system. Need a simple mechanical suggestion please. Currently the pipe is inserted into the coolant to ensure it does not spray coolant all over the place. Will clamping this pipe above the coolant level help?

 

[kunalv]

How do I know the foaming is caused by the Eductor? Well I have given a ball valve just before the Eductor and the eductor is on a bypass line. So when the valve is closed, there is no fluid going through the eductor thereby the suction of fluid from the tray stops and so does the foaming.

 

[jack action]

How about adding a line from the pump outlet (or directly from the tank, if gravity is your friend) to the tray with a float valve monitoring the coolant level in the tray? They can be as simple as this:

​

 

[Flyboy]

Hi guys, facing a bit of a problem here. Please see the system layout here :


I've connected an eductor to the coolant pump in my machine. This eductor sucks the leaked cutting fluid from a tray underneath the machine I.e coolant passes through the venturi(let's call it motive) and returns to the tank and in this process a vacuum is developed which is used to suck up the oil from the tray which travels with the motive and enters my tank.

Now the problem I'm facing here is once all the leakage oil has been sucked up the device keeps sucking air which is then effectively injected into the coolant sump thereby causing a lot of foam.

How can I prevent air from entering the tank? I cannot use any timers or solenoids to turn off the system. Need a simple mechanical suggestion please. Currently the pipe is inserted into the coolant to ensure it does not spray coolant all over the place. Will clamping this pipe above the coolant level help?

A fine mesh screen downstream of the venturi will cause the foam to stop and only allow liquid through, but it needs relatively low pressure differential across it.

It also has the benefit of acting as a debris filter, so you will want it to be accessible for regular inspection and cleaning.

 

[marcusl]

What if you place the tube above the surface of the oil in the tank instead of immersing it? Then the air won’t be injected into the oil.

 

[kunalv]

What if you place the tube above the surface of the oil in the tank instead of immersing it? Then the air won’t be injected into the oil.

This is what I am planning to try. The only problem with this is the pressure with which the liquid comes out of the pipe. Will have to make a simple clamp to hold it down.

 

[kunalv]

A fine mesh screen downstream of the venturi will cause the foam to stop and only allow liquid through, but it needs relatively low pressure differential across it.

It also has the benefit of acting as a debris filter, so you will want it to be accessible for regular inspection and cleaning.

The foam occurs when the liquid(and air) is injected into the liquid in the tank, and NOT when the liquid is flowing through the pipe

 

[sophiecentaur]

Would it be possible to arrange it so that all the pressures are positive? No air would be drawn in if the pump were below the liquid level in the drain tray. Does that make sense?
Alternatively use a level switch to turn off the pump when the level in the tray drops. if the unit serves more than one machine then the switch could operate a two way valve to recirculate from the main reservoir and not suck when a tray is empty.

 

[Ranger Mike]

Very good answers here. This is similar to running a dry sump oil system on a race car. The reservoir tank must has a vent t o atmosphere to prevent a vacuum. Do not permit the return oil line to be submersed or you will never eliminate air pockets in the return oil. Make it exit so it goes thru an oil separator permit the oil to drip to the tank after being separated from the air bubbles. In this case a fine mesh screen works wonders. The way it is most effective is to have the return oil splash on a sheet metal surface ( red disc in attached pic) and have the oil flow over the plate for a few inches to scrub of the air bubbles then it exits thru holes located on the side opposite the splash point. Super simple, effective, cheap. No valves, no switches, no levers to break, plain old physics. And it works!

 

[kunalv]

So, I tried keeping the return line a bit elevated to ensure it doesn't get submerged in the coolant, and it DID NOT help! The coolant still foams the moment all the oil from the tray has been transferred and my device starts sucking air.

I also thought I would try with a NRV above the Suction Cup in the tray, but even that wouldn't stop the air from going through (stupid of me to think it would work!)

 

[kunalv]

Very good answers here. This is similar to running a dry sump oil system on a race car. The reservoir tank must has a vent t o atmosphere to prevent a vacuum. Do not permit the return oil line to be submersed or you will never eliminate air pockets in the return oil. Make it exit so it goes thru an oil separator permit the oil to drip to the tank after being separated from the air bubbles. In this case a fine mesh screen works wonders. The way it is most effective is to have the return oil splash on a sheet metal surface ( red disc in attached pic) and have the oil flow over the plate for a few inches to scrub of the air bubbles then it exits thru holes located on the side opposite the splash point. Super simple, effective, cheap. No valves, no switches, no levers to break, plain old physics. And it works!

Could you share a photo of this fine mesh screen if possible? I don't think I could understand much from the illustration in your post.

Is it similar to those Oil Diffusers? Example -

 

[Ranger Mike]

https://www.triple-r-europe.com/product/quicktoron/

 

[pinball1970]

Hi guys, facing a bit of a problem here. Please see the system layout here :


I've connected an eductor to the coolant pump in my machine. This eductor sucks the leaked cutting fluid from a tray underneath the machine I.e coolant passes through the venturi(let's call it motive) and returns to the tank and in this process a vacuum is developed which is used to suck up the oil from the tray which travels with the motive and enters my tank.

Now the problem I'm facing here is once all the leakage oil has been sucked up the device keeps sucking air which is then effectively injected into the coolant sump thereby causing a lot of foam.

How can I prevent air from entering the tank? I cannot use any timers or solenoids to turn off the system. Need a simple mechanical suggestion please. Currently the pipe is inserted into the coolant to ensure it does not spray coolant all over the place. Will clamping this pipe above the coolant level help?

We used anti foaming agents/de-aerators in large dyeing vessels when this became an issue.

EDIT: These were water based liquors with organics in the suspension not oil based so surfactants would not work.

 

[Tom.G]

That triple-r separator is essentially a cyclone separator that requires a continuous and substantial oil flow to be effective.

I suggest using an additional small tank located above the main oil tank to act as a separator.

1) Have the recovered coolant drain into the small tank to de-gas.
2) In the small tank, install a float valve that drains into main tank only

when there is a substantial oil level.​

3) Position the float high enough to keep a significant oil level in the

small tank.​

4) You will need some deadband in the float valve, one approach

could be to use the height difference between the small & large tanks.​

4a) Run a hose or pipe from the small tank drain into the main tank so

that it is always submerged in the main tank.​

Hope this helps!
Tom

 

[Flyboy]

Could you share a photo of this fine mesh screen if possible? I don't think I could understand much from the illustration in your post.

Is it similar to those Oil Diffusers? Example - View attachment 351524

What size bubbles are you seeing in the foam? If they're in the 1mm or smaller range, that's the maximum mesh size you can use to get the desired effect.

You could seriously look at using a kitchen sink strainer to test the idea out and see how well it works. They're inexpensive, usually stainless steel and therefore should be compatible with your cutting fluid, and have a reasonably fine mesh to capture the foam.

Here's a sketch of how I'm envisioning the setup...

Take the output from the eductor venturi and feed it into the mesh screen in a large funnel at ambient conditions. Give yourself plenty of buffer space in the funnel above the screen, in case it backs up for whatever reason.

Ranger Mike is suggesting a system that does require constant flow and is more aimed at removing small amounts of air bubbles entrained in a system. Nothing against such a system, but it doesn't seem to be the right choice for this particular application.

 

[Ranger Mike]

I had to re-read original post. Can you turn down the suck rate to the point it lets an accumulation of fluid build up enuff so the suck pump does not start sucking air?