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Machine Coolant Sump Cleaning

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Machine Coolant Sump Cleaning

(This is a cleaning method for cleaning machine coolant sumps running water based machine coolants.  This is, perhaps, overkill in many cases but how much of this to do is your decision.  Filtering Your machine coolant will reduce the amount of work you may have to do when cleaning the sumps.  Take a look at some of the Machine Coolant Articles to find ways to keep coolant clean, or recycle and dispose of it once it is "used up".)

The main enemy of machine coolant is bacteria. Get rid of the breeding grounds for bacteria properly and you simplify your problems. The machine coolant should be filtered and recycled regularly. The machines also should drained and completely cleaned once each year.   This is the traditional figure.  With really good machine coolant management this may not be necessary.   

Collecting dirty machine coolant from the sump is made much easier and requires much less time when a sump vacuum or the filter system pump is used. The cleaning is also made more effective if the sump has rounded corners, with nowhere for microbes to hide, and is made of sheet metal construction. To prevent weekend growth of anaerobic bacteria be the machine coolant can be agitated and aerated to prevent anaerobic conditions from forming. 


1.   Treat the sump for bio‑contamination using a biocide / fungicide and following the manufacturer's procedures and recommendations.

2.   The old fluid with the biocide should be run for a minimum of 48 to 72 hours.

3.   The mixture should be dumped and disposed of safely and according to local, state and federal regulations. 


4.   Pump the sump out.

5.   Shovel out all swarf, fines and chips. 

6.   Clean any oily residues that remains on any surface.

7.   Clean as much as you can at this point.

All areas must be cleaned no matter how hard they are to reach.  Uncleaned areas provide a source of bacteria that rapidly attack the fluid used to refill the sump after cleaning.

8.   Add your cleaner.

9.   Always put water in first and add cleaner last to prevent foaming.

10.   Cleaner should be hot water mixed with a good alkaline machine cleaner.

  a.) Compatible with the metalworking fluid (in case some cleaner remains in the system after rinsing);

  b.) Low‑foaming to prevent pump cavitation, which is the sudden formation and collapse of low‑pressure bubbles induced by the pump's mechanical forces;

  c.) Resistant to short‑term rusting between cleanout and recharge.

11.  Circulate several hours to loosen and remove any hardened deposits, oily films, or gummy residues. The cleaner should run through the system just like the machine coolant for up to 3 hours.

12.   Hose down throughout the whole inside.

13.   While the cleaning solution is circulating, leaking equipment should be repaired.

14.   Clean the outside of the machine.

15.   Wipe down the outside with the same cleaner using a spritzer container at the same dilution ratio

16.   If possible, troublesome areas should be steam cleaned.

17.   Once this step has been completed the cleaner should be dumped. 


18.  Once the machine has been thoroughly cleaned and inspected, any residual cleaning solution must be rinsed from the equipment. Fresh water should be circulated through the system at least twice to rinse off any remaining cleaner.

19.  Wipe cleaning solution residues from the sump.

20.  Do the first rinse.

21.  To protect against flash rusting, a small amount of fluid concentrate (0.5% to 1.0%) should be added to the rinse water. This is done to prevent any flash rust.

22.  Wipe off cleaned surfaces that are not contacted by the rinse water cycling through the system.

23.  Do the second rinse.

Rinse water should then be placed in the system along with a 4.0 to 50:1 ratio of machine coolant to rinse the cleaning agent out.

24.  This should run for approximately 15 minutes.

25.  The interior of the machine should also be rinsed down with this solution. 

26.  The rinse water should also be disposed of properly. 


27.  During the rinsing you should mix up your machine coolant at the manufacturer's suggested ratio and have it ready to place into the system immediately after pumping out the rinsing agent.  You can also add another dose of biocide to start off.

28.   After it is completely drained of the rinse solution, the system can be charged with fresh fluid.

29.   The machine should then be turned on and run for about 30 minutes so as to get the machine coolant well dispersed on all parts of the exposed portions of the machining area.

30.   The fluid should then be circulated for at least 15 minutes prior to production. 

After One Week

31.   After running the machine for one (1) week, dump the machine coolant.

32.   Replace the machine coolant again at the manufacturer's recommendation