When a deep hole drilling machine sits idle for weeks or months, the coolant system does not simply wait — it changes. Water evaporates, concentration drifts, bacteria grow in stagnant coolant, seals dry and shrink, and debris settles at every low point. A systematic restart procedure prevents the problems that develop during idle periods from damaging the system when it starts again.
Pre-Restart Inspection
Visual Inspection
| Check Point | What to Look For | Action |
|---|
| Coolant level in tank | Low (evaporation) | Fill to operating level |
| Coolant appearance | Cloudy, separated, oily layer, mold | Assess — may need replacement |
| Coolant odor | Rotten eggs, sour, rancid | Bacteria present — flush system |
| Tank interior | Sludge, sediment, mold | Clean tank |
| Exposed metal surfaces | Rust on machine ways, fixtures | Clean, apply rust preventive |
| Hoses and seals | Cracks from drying, leakage | Replace damaged hoses and seals |
| Wipers (way) | Hardened from coolant drying | Replace if hardened |
| Chip conveyor | Chips dried and packed | Clean chip conveyor |
Coolant Condition Assessment
| Test | Result | Action |
|---|
| Concentration | > 5% and < 12% | Adjust to target |
| Concentration | < 5% | Add concentrate (check pH and bacteria first) |
| pH | < 8.0 | Bacteria likely — flush system recommended |
| pH | 8.0–9.5 | Acceptable — can be adjusted |
| Bacteria (dip slide) | > 10^5 CFU/mL | Sanitize or flush system |
| Tramp oil | > 5% | Remove oil, flush if heavy |
| Visual clarity | Cloudy or separated | Flush system — replace coolant |
Flush Decision Guide
| Condition | Action |
|---|
| Shutdown < 2 weeks, coolant OK | No flush needed — check concentration and start |
| Shutdown 2–4 weeks, coolant looks OK | Test pH and bacteria — flush if marginal |
| Shutdown 2–4 weeks, coolant questionable | Flush recommended |
| Shutdown > 4 weeks | Flush recommended — regardless of appearance |
| Shutdown > 8 weeks | Flush required — drain and replace coolant |
| Any bacterial contamination | Flush + sanitize required |
System Flushing Procedure
Full System Flush
| Step | Action | Detail |
|---|
| 1 | Drain old coolant completely | Pump out, open all drain plugs |
| 2 | Remove and clean filter elements | Replace disposable filters |
| 3 | Clean tank interior | Remove sludge, pressure wash |
| 4 | Fill with clean water | Treated water preferred |
| 5 | Add flushing detergent | Per manufacturer recommendation |
| 6 | Run circulation pump for 30 minutes | Full system circulation |
| 7 | Open all drain points briefly | Flush low points |
| 8 | Continue circulation for 15 more minutes | — |
| 9 | Drain flush water completely | — |
| 10 | Refill with fresh coolant | At operating concentration |
| 11 | Run circulation for 15 minutes | Check for leaks |
| 12 | Verify coolant concentration and pH | Adjust if needed |
Component Checks
Pump Check
| Check | Method | Acceptable | Action if Failed |
|---|
| Shaft rotation | Turn by hand | Free rotation — no binding | If seized, pump may be frozen or corroded |
| Seal condition | Visual | No cracks, no leakage | Replace seal |
| Priming | Fill pump housing with coolant | Primed | Open vent, fill before starting |
| Coupling alignment | Visual and feel | No misalignment | Align coupling |
| Mounting bolts | Wrench check | Tight | Tighten |
Seal and Gasket Check
| Component | Effect of Shutdown | Action |
|---|
| Rotary union seal | Dries and shrinks — leaks on startup | Replace if > 1 year old or leak is detected |
| Coolant collar seals (BTA) | Dries and hardens | Replace if hard or cracked |
| Pump shaft seal | May leak on first startup | Run 30 minutes — if still leaking, replace |
| Valve stem seals | May shrink | Check for leaks during startup |
| Hose O-rings at fittings | May shrink | Check for leaks during startup |
| Tank cover gasket | Usually OK | Visual check |
Filter Check
| Filter Type | Shutdown Effect | Action |
|---|
| Cartridge filter | Usually OK — may have dried debris | Replace if > 3 months old |
| Bag filter | May have dried contaminants | Replace |
| Suction strainer | Debris may have settled and dried | Clean before startup |
| Magnetic separator | OK | Clean magnet surface |
Heat Exchanger Check
| Check | Method | Action |
|---|
| Pressure test (both sides) | Close valves, observe pressure | Replace if leaking |
| Cleanliness | Compare pressure drop to baseline | Clean if pressure drop > 25% above baseline |
| Chiller water | Check water/glycol level and concentration | Top up, check freeze protection |
Startup Sequence
Initial Startup
| Step | Action | Check |
|---|
| 1 | Verify all drain plugs are closed | — |
| 2 | Fill coolant to normal level | At operating concentration |
| 3 | Prime pump (if not self-priming) | Fill pump housing, open vent |
| 4 | Jog pump motor — 2 seconds on, 10 seconds off | Listen for smooth operation |
| 5 | Run pump at low speed (if variable speed) | 5 minutes at 50% speed |
| 6 | Check for leaks at all connections | Immediate — before pressure builds |
| 7 | Increase to operating speed | — |
| 8 | Check pressure builds normally | Compare to baseline |
| 9 | Check flow at return line | Normal return flow |
| 10 | Check heat exchanger operation | Temperature should stabilize |
Post-Startup Monitoring
| Check | Frequency After Restart | Acceptable |
|---|
| System pressure | Every 15 minutes for 1 hour | Stable at target |
| Leaks — all connections | Every 15 minutes for 1 hour | No leaks |
| Pump noise | Every 30 minutes for 2 hours | Normal — no cavitation |
| Coolant temperature | Every 30 minutes for 2 hours | Rising to normal, then stabilizing |
| Coolant concentration | After 1 hour of circulation | At target ± 0.5% |
| Coolant pH | After 2 hours | 8.5–9.5 |
| Filter ΔP | After 1 hour | Clean baseline |
Drilling Restart
| Step | Action | Reason |
|---|
| 1 | Run spindle warm-up (30 minutes) | Redistribute lubrication |
| 2 | Jog all axes full stroke | Check for binding from dried lubrication |
| 3 | Check way lubrication | Verify oil is flowing to all points |
| 4 | Drill one test hole at reduced parameters | Verify system function |
| 5 | Inspect test hole | Check diameter, surface finish, chip shape |
| 6 | Inspect chips | Verify normal chip form |
| 7 | Increase to normal parameters | If test hole is acceptable |
| 8 | Monitor first 5 production holes closely | Verify stability |
Common Restart Problems
| Problem | Likely Cause | Corrective Action |
|---|
| Pump cavitation | Air in suction line, low coolant level | Prime pump, check tank level, bleed air |
| Seal leak on startup | Seal dried and shrank during shutdown | Run 30 minutes — if leak continues, replace seal |
| Low pressure | Air in system, filter partially clogged | Bleed air, check filter |
| High pressure | Blocked line from settled debris | Flush lines |
| Coolant foaming | Degraded coolant, air entrainment from startup | Check concentration, check for air leaks |
| Bacteria odor | Bacterial growth during idle | Flush and sanitize system |
| Pressure fluctuations | Air in system, pump cavitation | Bleed air, check pump prime |
FAQ
How do I restart a deep hole drilling coolant system after a long shutdown?
Step 1: Inspect the coolant — check appearance, odor, pH, and bacteria. If shutdown exceeded 4 weeks, flush and replace coolant. Step 2: Clean the tank, replace filters, prime the pump. Step 3: Fill with fresh coolant, start the pump at low speed, check for leaks. Step 4: Increase to operating speed, verify pressure and flow. Step 5: Run spindle warm-up, jog axes, drill a test hole. Monitor the first few hours of operation closely.
What happens to coolant during an extended shutdown?
Water evaporates (concentration increases), bacteria grow in stagnant coolant (especially if coolant was marginal before shutdown), tramp oil separates and floats to the surface, fine particles settle in low points (tank bottom, pipe low points), pH drops from bacterial activity, and additives degrade. After 4+ weeks of idle time, the coolant is unlikely to be in good condition.
How do I check if coolant is still good after a shutdown?
Test four things: appearance (clear or cloudy, separation), odor (normal or rotten/sour), pH (acceptable range 8.0–9.5), and bacteria count (dip slide — acceptable < 10^4 CFU/mL). If any test fails, flush and replace coolant before restarting. The cost of a coolant change is far less than the cost of troubleshooting problems caused by degraded coolant.
Do I need to replace seals after an extended shutdown?
Inspect all seals — rotary union, pump shaft seal, coolant collar seals, hose O-rings — for cracks, hardening, or deformation. Seals that were marginal before shutdown will likely fail on restart as they shrink during the idle period. Replace any seal that shows signs of drying or cracking. Rotary union seals are the most critical — a rotary union leak on startup can flood the spindle bearings.
Why does my coolant foam after restarting?
Foaming after restart is caused by: degraded coolant (additives broke down during idle), air entrainment (air in the system from draining and refilling), contaminants (dried residue dissolving into new coolant), or coolant concentration too high (evaporation during idle increased concentration before shutdown). Run the system for 30–60 minutes to purge air, check concentration, and add anti-foam if needed. If foaming persists, the coolant may need replacement.
A systematic coolant system restart after extended shutdown prevents the problems that develop during idle periods — seal leaks, pump cavitation, bacteria contamination — from damaging the system when it starts again. Inspect before starting, flush if the coolant has been idle more than 4 weeks, and monitor closely for the first few hours of operation. This article reflects industry practice as of 2026.
