The coolant pump in a deep hole drilling machine is the single most critical component of the coolant system — and the most common source of performance problems. A pump that is incorrectly sized, poorly installed, or operated outside its design range will cavitate, vibrate, wear rapidly, and deliver inconsistent coolant to the drill. Selecting the right pump type and installing it correctly is the foundation of a reliable coolant system.
Pump Types
Pump Design Comparison
| Pump Type | Pressure Range | Flow Range | Efficiency | Solids Handling | Best For | Limitations |
|---|
| Centrifugal — end suction | Up to 20 bar | 50–500 L/min | 60–80% | Limited — clean coolant recommended | General coolant transfer — low-pressure systems — central systems | Low pressure — limited solids handling |
| Centrifugal — multistage | Up to 100 bar | 20–200 L/min | 65–80% | Limited — clean coolant required | High-pressure coolant — single machine — moderate flow | Higher cost — complex — sensitive to debris |
| Vertical turbine pump | Up to 50 bar | 50–1000 L/min | 70–85% | Moderate — submerged design handles some solids | Deep tanks — limited floor space — submerged installation | Long lead time — difficult to service — shaft alignment critical |
| Screw pump (progressive cavity) | Up to 50 bar | 5–200 L/min | 50–70% | Excellent — handles high solids — viscous fluids | Sludge transfer — chip-laden coolant — tramp oil removal | Lower efficiency — stator wears — pulsating flow at low speed |
| Piston pump (plunger) | Up to 500+ bar | 2–50 L/min | 80–90% | Limited — clean coolant only | Ultra-high-pressure coolant — precision drilling — small diameter drills | Pulsating flow (requires damper) — expensive — high maintenance |
| Diaphragm pump | Up to 20 bar | 5–100 L/min | 40–60% | Excellent — handles solids — can run dry | Transfer service — sludge pumping — temporary coolant circulation | Pulsating flow — low efficiency — limited pressure |
Recommended Pump by Application
| Application | Recommended Pump Type | Reason |
|---|
| Low-pressure coolant (5–15 bar) — single machine | End suction centrifugal | Simple — reliable — low cost — adequate pressure for low-pressure systems |
| Medium-pressure coolant (15–50 bar) — single machine | Multistage centrifugal | Provides required pressure — smooth flow — good efficiency |
| High-pressure coolant (50–200 bar) — single machine | Multistage centrifugal — or piston pump | Multistage for moderate high-pressure — piston for ultra-high-pressure and precision |
| Central coolant system — multiple machines | End suction centrifugal (large) + pressure booster for high-pressure machines | Large centrifugal handles total flow — booster provides high pressure where needed |
| Coolant transfer — tank filling — sludge removal | Screw pump — diaphragm pump | Handles solids — can run dry — self-priming capability |
| High-solids coolant — chip-laden fluid | Screw pump — vertical turbine (submerged) | Open flow path — solids pass through without jamming |
Sizing Calculations
Total Dynamic Head (TDH)
| Component | Description | Calculation Method | Example (m) |
|---|
| Static suction head | Vertical distance from liquid level to pump centerline | Measure — positive if liquid level is above pump, negative (suction lift) if below | +0.5 m (flooded suction) |
| Static discharge head | Vertical distance from pump centerline to highest discharge point | Measure vertical rise from pump to highest point in discharge piping | +5.0 m |
| Friction loss — suction piping | Pressure loss in suction pipe, fittings, strainer | Calculate per pipe size, length, fittings — use friction loss tables | +0.5 m |
| Friction loss — discharge piping | Pressure loss in discharge pipe, fittings, valves, hoses, coolant union, drill | Calculate total equivalent length — use friction loss tables | +15.0 m |
| Pressure required at drill | Backpressure required for drilling operation | From drill manufacturer — typically 20–200 bar | +200 m (for 20 bar) |
| Velocity head | Kinetic energy in discharge | V²/2g — usually negligible | +0.5 m |
| Total Dynamic Head | Sum of all components | Add all above | ~221.5 m |
NPSH Available (NPSHa)
| Parameter | Symbol | Value | Notes |
|---|
| Atmospheric pressure | Patm | 10.3 m (at sea level) | Reduces with altitude — 1 m per 1000 m elevation |
| Liquid surface pressure | Pvapor | 0.3 m (coolant at 30°C) | Increases with temperature — higher temperature = higher vapor pressure |
| Static suction head | Hs | +0.5 m | Positive if liquid level above pump centerline |
| Suction friction loss | Hf | 0.5 m | Pipe, fittings, strainer losses |
| NPSHa | Patm + Hs − Hf − Pvapor | 10.3 + 0.5 − 0.5 − 0.3 = 10.0 m | Must exceed NPSHr by minimum 1.0 m |
Power Requirement
| Formula | Variable | Description | Units |
|---|
| P = (Q × H × SG) / (367 × η) | Q | Flow rate | m³/h |
| H | Total dynamic head | m |
| SG | Specific gravity | dimensionless (coolant ≈ 1.0) |
| η | Pump efficiency | decimal (0.65 = 65%) |
Example: Q = 10 m³/h (166 L/min), H = 220 m, η = 0.70: P = (10 × 220 × 1.0) / (367 × 0.70) = 8.6 kW — select 11 kW motor minimum.
Installation Requirements
Foundation and Baseplate
| Requirement | Specification | Reason |
|---|
| Foundation mass | 3–5× pump and motor mass | Absorbs vibration — prevents movement — maintains alignment |
| Foundation material | Concrete — minimum 28-day cure before pump installation | Stable base — no settling after installation |
| Foundation bolts | Embedded — sized per pump vendor drawing | Secures baseplate — prevents shifting |
| Baseplate | Grouted to foundation — not shimmed only | Full grout support prevents baseplate distortion |
| Grouting | Non-shrink grout — full contact under baseplate | Even load distribution — prevents baseplate from bending |
| Leveling | Baseplate level within 0.2 mm/m | Maintains pump and motor alignment |
| Anchor bolt torque | Per bolt size and grade — torque wrench | Even clamping — prevents vibration loosening |
Suction Piping Design
| Guideline | Recommendation | Consequence of Non-Compliance |
|---|
| Suction pipe diameter | One to two sizes larger than pump suction nozzle | Undersized suction causes cavitation — limits flow |
| Suction pipe length | Minimum 5× pipe diameter of straight pipe before pump inlet | Turbulence at pump inlet causes cavitation — reduces pump life |
| Suction strainer | 3–5 mm perforations — 3–5× pump suction area | Undersized strainer causes cavitation — no strainer allows debris to damage pump |
| Suction isolation valve | Full-port gate or ball valve — never use globe or needle on suction | Restrictive valve on suction causes cavitation |
| Suction elbows | Minimum 5× pipe diameter radius — no elbows at pump inlet if possible | Flow disturbance at impeller eye causes cavitation — reduces pump performance |
| Suction slope | Continuous upward slope from tank to pump (flooded suction) | Air pockets in suction line cause cavitation |
| Tank connection | Above tank bottom — not at bottom | Prevents sediment from entering pump suction |
| Air vent | At high point of suction line | Air trapped in suction prevents pump from priming |
Discharge Piping Design
| Guideline | Recommendation | Reason |
|---|
| Discharge pipe diameter | Same size as pump discharge nozzle — or one size larger | Undersized discharge increases velocity — increases friction loss |
| Check valve | Installed between pump discharge and isolation valve | Prevents backflow when pump stops — prevents reverse rotation |
| Isolation valve | Gate valve or ball valve on discharge | Allows pump service without draining system |
| Pressure gauge | Installed at pump discharge — between pump and check valve | Measures actual pump discharge pressure — before check valve |
| Flow meter | Installed downstream of all valves — in straight pipe | Accurate flow measurement — requires straight pipe upstream |
| Piping supports | Support pipe independently — do not hang on pump nozzles | Pipe weight on pump causes misalignment — stresses casing |
| Thermal expansion | Allow for expansion in long pipe runs — use expansion joints | Rigid piping expands when coolant is hot — stresses connections |
| Relief valve | If discharge can be blocked with pump running | Protects pump and piping from overpressure |
Alignment and Coupling
| Step | Action | Tolerance | Method |
|---|
| 1 | Rough alignment — after baseplate grouted | ±0.5 mm | Straightedge across coupling |
| 2 | Fine alignment — after piping connected | Angular: ±0.05 mm/mm — Parallel: ±0.05 mm | Dial indicator on coupling halves |
| 3 | Thermal growth check | Account for motor thermal expansion | Offset alignment opposite to expected growth |
| 4 | Final alignment — after pump reaches operating temperature | Angular: ±0.05 mm/mm — Parallel: ±0.05 mm | Hot alignment check — recheck after 1 week of operation |
| 5 | Coupling installation | Per manufacturer specification | Lubricate if required — verify gap |
Startup and Commissioning
| Step | Action | Detail |
|---|
| 1 | Verify pump rotation | Bump motor — check rotation arrow on pump casing — correct if wrong |
| 2 | Verify suction piping complete | Tank full — suction valve fully open — no air leaks |
| 3 | Verify discharge piping complete | Discharge valve partially open (20%) — check valve installed correctly |
| 4 | Prime pump | Flood suction — open vent at pump casing — close when coolant flows steady |
| 5 | Start pump | Start motor — immediately check pressure builds — if no pressure within 5 seconds, stop and re-prime |
| 6 | Open discharge valve gradually | To 100% — check pump pressure at each step — listen for cavitation (rattling) |
| 7 | Check for leaks | All connections — pump shaft seal — piping joints |
| 8 | Check pump operation | Pressure — flow — motor current — vibration — noise — all within spec |
| 9 | Run at full flow for 30 minutes | Monitor pump temperature — bearing temperature — seal condition |
| 10 | Final alignment check | Recheck coupling alignment — tighten foundation bolts — check for soft foot |
| 11 | Record baseline data | Flow — pressure — motor amps — vibration level — date — for future comparison |
Troubleshooting
| Problem | Symptom | Likely Cause | Corrective Action |
|---|
| No flow — pump runs | Pressure zero — no coolant at drill | Pump not primed — suction blocked — rotation wrong | Prime pump — check suction strainer — verify rotation direction |
| Low flow — pressure low | Flow below spec — pressure below spec | Worn impeller — air leak on suction — partial suction blockage | Check impeller clearance — check suction line for air leaks — clean strainer |
| Low flow — pressure normal | Flow below spec — pressure at spec | Discharge restriction — clogged drill — valve partially closed | Check discharge piping — check drill — verify valve position |
| Pump cavitation | Rattling noise — pressure fluctuation | NPSH insufficient — suction strainer blocked — tank level low | Clean strainer — raise tank level — verify NPSHa > NPSHr |
| Pump vibration | Excessive vibration — noise | Misalignment — imbalance — bearing wear — cavitation | Check alignment — balance coupling — replace bearings — fix cavitation |
| Pump shaft seal leak | Coolant drip at shaft | Seal wear — shaft surface worn — incorrect seal for coolant | Replace seal — check shaft surface — verify seal material compatibility |
| Bearing overheating | Bearing housing hot — > 80°C | Over-lubrication — under-lubrication — misalignment — bearing failure | Check lubrication — verify alignment — replace bearing if noisy |
| Motor overload | Motor trips on overcurrent | Pump running beyond design point — coolant too viscous — misalignment | Check valve position — verify specific gravity — align pump and motor |
FAQ
What type of coolant pump is best for deep hole drilling?
The best coolant pump type for deep hole drilling depends on the required pressure and flow: for low-pressure systems (5–15 bar), an end suction centrifugal pump is the best choice — it is simple, reliable, low cost, and widely available. For medium-pressure systems (15–50 bar), a multistage centrifugal pump is the standard choice — it provides the required pressure with smooth, non-pulsating flow and good efficiency. For high-pressure systems (50–200+ bar), a multistage centrifugal pump is the most common choice for flows above 20 L/min — for very high pressure (200+ bar) or low flow (under 20 L/min), a piston pump may be specified but requires a pulsation damper. The multistage centrifugal pump is the most commonly used pump in deep hole drilling coolant systems because it offers the best combination of pressure capability, flow range, efficiency, and smooth flow. Key selection factors: the pump must handle the required pressure and flow simultaneously (check the pump curve — not just maximum pressure and maximum flow separately — the pump must deliver the required flow at the required pressure). The pump must be compatible with water-based coolant (316 stainless steel or bronze internals — carbon ceramic seals). The pump must have adequate NPSH margin (NPSHa must exceed NPSHr by at least 1.0 m — this is often the limiting factor in pump selection for coolant applications).
How do I calculate the correct coolant pump size for my deep hole drilling machine?
To calculate the correct coolant pump size: determine the required flow rate (drill diameter × 0.5–1.5 L/min per mm — for a 20 mm drill, 10–30 L/min — confirm with drill manufacturer). Determine the required pressure at the drill (from drill manufacturer — typically 20–100 bar for gun drilling — 10–50 bar for BTA drilling). Calculate the total dynamic head (TDH) — the sum of: static head (vertical lift from pump to drill — typically 2–5 m), friction loss in piping (suction and discharge piping, valves, fittings — typically 5–20 m depending on pipe length and size), pressure required at the drill (the major component — 20 bar = 200 m head, 50 bar = 500 m head, 100 bar = 1000 m head). Select a pump whose curve shows the required flow at the TDH. For example: required flow 25 L/min at 50 bar (500 m head) — look for a multistage centrifugal pump with a curve that delivers at least 25 L/min at 500 m. Check NPSHr (required NPSH) from the pump curve at the operating point — verify NPSHa (available NPSH) exceeds NPSHr by at least 1.0 m. Calculate power: P (kW) = (Q × H × SG) / (367 × η) — select a motor with 10–15% margin above calculated power. The most common sizing error is selecting the pump based on maximum pressure only — without checking that the pump delivers the required flow at that pressure. A pump's maximum pressure (at zero flow) is not the same as its pressure at the required flow — always check the pump curve at the operating point.
How important is suction piping design for coolant pump reliability?
Suction piping design is the most critical factor in coolant pump reliability — more important than pump brand or quality. The most common cause of pump failure in coolant systems is cavitation caused by poor suction piping design. Key suction piping rules: the suction pipe must be one to two sizes larger than the pump suction nozzle (reduces velocity — reduces friction loss — reduces cavitation risk). The suction pipe must have at least 5 pipe diameters of straight pipe before the pump inlet (elbows or tees at the pump inlet cause turbulent flow into the impeller — turbulence causes cavitation — the straight pipe allows the flow to stabilize). The suction strainer must have 3–5× the pump suction area (an undersized strainer creates high friction loss — especially as it loads with debris — this reduces NPSHa and causes cavitation). The suction line must have a continuous upward slope from the tank to the pump (any high point traps air — air in the suction line causes cavitation and prevents priming). The pump must have flooded suction (coolant level above pump centerline) if possible — suction lift (pump above tank) significantly increases cavitation risk. The suction isolation valve must be a full-port gate or ball valve (any restriction in the suction line reduces NPSHa — globe valves and needle valves are too restrictive for suction service). If these rules are followed, most cavitation problems are eliminated before the pump ever starts.
Why does my coolant pump lose prime and how do I fix it?
A coolant pump loses prime when air enters the suction line or the pump casing — the pump can no longer create the vacuum needed to draw coolant from the tank. Common causes: suction line air leak (loose flange — cracked pipe — damaged O-ring at pump suction — air is drawn into the suction line and replaces coolant in the pump casing). Low tank level (the coolant level in the tank drops below the suction pipe inlet — air enters the suction line — the pump loses prime). Vortexing at the tank outlet (the pump draws coolant faster than the tank can supply — a vortex forms at the suction pipe inlet — air is drawn into the suction). Leaking pump shaft seal (the shaft seal is the most common air leak point on a pump — a worn seal allows air to enter the pump casing — the air replaces coolant and the pump loses prime). To fix a pump that has lost prime: stop the pump — fill the pump casing with coolant through the vent port (re-priming) — start the pump — if it builds pressure and flow, the pump is primed. If it loses prime again: check the tank level and fill if needed — check the suction line for air leaks (look for wet spots, drips, or bubbles at connections) — check the pump shaft seal for leakage (coolant drip is obvious — air ingestion is not visible but causes repeated loss of prime) — check for vortexing at the tank outlet (install a vortex breaker or increase tank level). If the pump repeatedly loses prime, the most likely cause is a suction line air leak — pressurize the suction line and check all connections with soap solution (bubbles indicate the leak) or submerge the suction line and look for bubble streams.
How do I maintain a deep hole drilling coolant pump?
Coolant pump preventive maintenance: daily — check pump pressure and flow (compare to baseline — a gradual decrease indicates wear or filter loading). Check for unusual noise or vibration (changes in sound indicate developing problems — cavitation noise, bearing noise, coupling noise). Check shaft seal for leaks (some seepage is normal with mechanical seals — a steady drip indicates seal wear). Weekly — check and clean the suction strainer (a partially blocked strainer causes cavitation — clean at least weekly — more often if coolant has high debris content). Check coupling alignment (misalignment causes vibration and coupling wear — recheck after any piping work). Check motor current (compare to nameplate rating — high current indicates pump running beyond design point). Monthly — lubricate pump bearings per manufacturer's schedule (use correct grease type and quantity — over-lubrication is as harmful as under-lubrication). Check and tighten foundation bolts (vibration can loosen bolts over time). Check and clean pump cooling passages (if pump has water-cooled bearing housing). Annually — replace pump shaft seal (preventive replacement before failure — seal wear accelerates after 12–18 months). Replace coupling element (elastomer couplings wear — replace annually regardless of appearance). Check impeller clearance (wear rings — measure clearance to OEM spec — replace if clearance exceeds limit). Inspect pump internals (impeller, wear rings, diffusers — replace worn components). Check alignment (hot alignment — with pump at operating temperature). Record all maintenance data (pressure, flow, motor amps, vibration — trend data identifies developing problems before they cause failure).
The coolant sump pump is the heart of the deep hole drilling coolant system. Select the correct pump type for the pressure and flow requirements — multistage centrifugal for most applications. Size the pump using total dynamic head — not just pressure rating. Design the suction piping with care — flooded suction, oversized pipe, straight runs, properly sized strainer. Install on a grouted baseplate with correct alignment. Start up with proper priming and verification. Maintain with regular seal checks, strainer cleaning, and annual component inspection. A properly selected and installed coolant pump delivers years of reliable service — the foundation of consistent deep hole drilling performance. This article reflects industry practice as of 2026.
