I am designing a liquid dispensing system for CNC machines that will top-up a mixed solution of coolant & water at the required concentration.

Present concentration in the machine sump will almost always be richer than required, so I need to 'dose' the makeup liquid at a concentration of 2-3% to balance the concentration in the sump.

Water will be supplied under gravity through the plant's service line while the coolant shall be pumped from a barrel. I don't know if infeed of coolant can be automated as well since I've been trying to work on this for a while now and have not been able to come up with any viable solutions.

I have done received some data from clients wherein I have concluded the following :-

  1. Daily top-up is done once in the morning (start of the first shift).
  2. Top-up volumes range from 20-50 Litres.

So a daily top-up of 20-50 Litres @ concentration of 2-3% is what is required. Water flowing under gravity has to be mixed in-line with the coolant and the mixed solution supplied to the tank through a hose. I cannot have an intermediate mixing tank as there is severe crux for space, so the mixing has to be done in the pipes.

Queries :-

  1. I have thought about using an Injection Quill to inject the coolant concentrate into the water pipe, but i am not sure if it will help.

  2. Also, a dosing pump will dose in pulses, while the water flow is continuous. Can I get the right mixing efficiency in such a case?

  3. Will Hall-Effect Turbine flow sensors be accurate enough for such an application to sense the flow-rate?

  4. Are there any compact motorized valves I can use to throttle the flow of water?

  5. I am planning to use a Capacitive Level Transmitter inserted into the tank to know the volume of liquid present and how much will be required.

  6. The present concentration in the tank shall be fed into the HMI by the user. The PLC will then actuate the process with these parameters viz. makeup volume and concentration.

If someone can guide me as to how I can incorporate all this into a workable solution, I'd be forever grateful.



  • $\begingroup$ Systems like this exist - check out the water treatment systems for boilers... used to treat the hardness... $\endgroup$
    – Solar Mike
    Sep 12 '19 at 8:49
  • $\begingroup$ Can you use a dosing pump for water as well? then you know the ratio. And how does the user know the present concentration? $\endgroup$
    – user253751
    Feb 10 '20 at 17:55

While it's possible to have a tank of coolant concentrate and mix inline if you have so much work to do that automation is practical and manual checking is impractical then you should consider a coolant recycling system.

As you have noticed, using inline mixing is still going to require checking the machines; either manually or automatically. What you end up with is coolant with slowly deteriorating properties until you flush out periodically and occasionally have entirely fresh and properly mixed coolant. As a point of interest, lots of places (most places?) do exactly that.

With a recycling system you can remove mechanically dispersed fines and tramp oils which wear and gum up the equipment. Using a refractometer the concentration of purified and properly mixed coolant can be maintained all the time, instead of a varying and deteriorating coolant you can always have good coolant.

A quote from a website offering equipment to recycle the coolant:

"The AC3 works exclusively in conjunction with the PRAB Guardian Central Coolant Recycling System. The Guardian uses a comprehensive coalescing filtration process, effectively removing mechanically dispersed tramp oils to 0.1% or less. The Guardian Coolant Recycling System has demonstrated a reduction in haul-away costs by 90%, and has lowered new coolant purchase up to 75%. Payback on equipment purchase is typically 6-9 months.

A different website, "FSI - CRS - Coolant Recycling System" offers a well explained breakdown of costs and savings: the cost of new coolant, hauling away used coolant, and disposal can be significant, let alone the wear and tear on the machines and slight variances that might result in the finished parts.

That second site has a photo of what a simple system might look like and also offers a block diagram. They claim an 8 month payback.

Coolant Recycling


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