Coolant tank/reservoir of a machine tool (the sump the coolant lives in, and the clean-out that sets its life)
The coolant tank under a machine tool, built and kept so it can be cleaned out · where bacteria live in a sump, machine cleaner circulation times, rinse with water or a weak coolant, recharge without diluting, and what the tank needs to make that possible
A machine tool's coolant tank holds the working fluid, settles chips and feeds the pump. Its condition decides how long the coolant lasts: residue on the walls and in the plumbing carries bacteria that a fresh charge picks up again. Fluid suppliers publish clean-out procedures, and the tank and its plumbing have to allow them to be carried out.
Coolant tanks (sumps) of individual machine tools and their clean-out and recharge. The machine-side coolant system with filtration and flood supply is covered on the Coolant system for CNC machine tools: machine-side tank, filtration and flood-coolant supply unit page; central systems on the Central coolant management system for a machine-tool hall: one filter plant and supply header feeding a row of CNC machines, sized in litres page; portable filter carts on the Filter unit for machine tool coolant: a portable pump-and-bag cart that cleans each sump in turn page; skimmers on the Tramp oil skimmer for machine coolant page; storage tanks as a product family on the Storage tank page.
CNFX editorial research · Sources checked October 13, 2026 · 2 sources
Master Fluid Solutions' Technical Bulletin #052 states that "It has been estimated that at any given time less than 1% of the total microbiological load in a machine tool is actually circulating in the fluid"; the rest lives in residue on sump walls and bottoms and in the delivery plumbing, where biocides penetrate only a short distance. [1]
The bulletin separates this periodic cleaning from the quick pump-out at a fluid change. It treats the chip conveyor as part of the job: "Typically 100% of the fluid put up into the cutting zone passes through the conveyer before it reaches the sump", so a dirty conveyor reinoculates the fresh charge. It calls the cleaning "annual" as a planning number and says it "should be scheduled as often as necessary", depending on what is cut, use, sump design and maintenance. [1]
Before cleaning, DuBois asks for supplementary tanks to be inspected for "dead areas (cracks/open seams) which may lead to pockets of stagnant fluid", and for tramp oil to be skimmed before the tank is drained. [2]
Ask the machine or tank supplier how the sump is accessed for cleaning (removable covers, drain point at the low point, conveyor removal), and whether the tank has corners or seams where fluid stands.
02
Circulate cleaner, rinse, and recharge without diluting
Master Fluid Solutions describes a five- or seven-step process. For a dirty system it pumps out the old fluid, removes chips, charges the sump with machine cleaner and circulates it "for as long as possible (3 hours minimum)", washes down the machine, opens it up to clean conveyors and guarding, pumps out, rinses with fresh water through all plumbing, and recharges. [1]
Master Fluid Solutions warns that after the rinse "The cleaning process has stripped all the oil and rust protection off of the machine", so recharging follows quickly, and that the first few gallons from each coolant nozzle should be caught so they do not dilute the new charge. [1]
DuBois' procedure for individual machines adds cleaner at 2% and circulates it for 1–8 hours depending on the soils, then refills with a 1.0% coolant solution to flush out cleaner and debris before charging at the recommended concentration; for central systems it circulates a 3% cleaner for 2–4 hours. Its central-system text says "Following step 7" under a step numbered 4, so the step order there should be confirmed with DuBois. [2]
Agree the cleaner and its concentration with the coolant supplier, and confirm the tank drain, rinse volume and waste disposal route before the first clean-out.
03
Coolant tank details
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Compiled and source-reviewed by the CNFX editorial team.
Each manufacturer above links to the page on that company's own website where the product is listed, with the date we checked it. How we source and review
· Page last updated 13 October 2026
Buyer questions
Where do bacteria in a coolant system live?
Master Fluid Solutions estimates less than 1% circulate in the fluid; the rest live in residue on sump walls and plumbing. [1]
How long should machine cleaner circulate?
At least 3 hours per Master Fluid Solutions; DuBois gives 1–8 hours for individual machines, by soil level. [1][2]
Rinse with water or coolant?
Master Fluid Solutions rinses with fresh water; DuBois flushes with a 1.0% coolant solution. [1][2]
Why recharge quickly after rinsing?
The cleaning strips oil and rust protection from the machine, according to Master Fluid Solutions. [1]
Sources and what still needs a direct check
Sources checked 2026-10-13. Master Fluid Solutions publishes Technical Bulletin #052 on cleaning machine tool sumps; DuBois Chemicals publishes its sump clean-out procedures for metalworking systems.
