The coolant pump is the heart of a deep hole drilling system. Without adequate coolant pressure and flow, chip evacuation stops, tool life drops, and hole quality degrades. Choosing the right pump type is one of the most consequential decisions in deep hole drilling machine design and retrofitting.
Pump Type Overview
Comparison Table
| Characteristic | Screw Pump (Progressive Cavity) | Piston Pump (Axial or Radial) | Centrifugal Pump |
|---|
| Pressure range | 10–100 bar (low to moderate) | 50–350 bar (moderate to very high) | 2–30 bar (low) |
| Flow range | 10–500 L/min (moderate) | 5–200 L/min (low to moderate) | 50–5,000 L/min (high) |
| Pressure/flow characteristic | Flat — pressure independent of speed | Flat — pressure controlled by valve | Steep — pressure depends on flow |
| Efficiency | 60–80% | 80–92% | 50–75% (at best point) |
| Particle tolerance | Good — handles moderate fines | Poor — clean coolant required | Excellent — handles heavy contamination |
| Pulsation | Low — continuous flow | Moderate to high — depends on piston count | None — continuous flow |
| Maintenance interval | 2,000–4,000 hours | 1,000–3,000 hours | 5,000–10,000 hours |
| Cost per unit pressure | Moderate | High | Low |
| Noise level | Moderate | High (requires enclosure) | Low |
Screw Pumps (Progressive Cavity)
Operating Principle
| Feature | Description |
|---|
| Mechanism | Single helical rotor turns inside a double-helix stator — creates progressive cavities that move fluid axially |
| Flow characteristic | Positive displacement — flow is proportional to speed, nearly independent of pressure |
| Self-priming | Yes — good suction lift capability |
| Particle handling | Good — flexible stator accommodates moderate particulate loads |
Application in Deep Hole Drilling
| Application | Suitability | Why |
|---|
| Gun drilling (low pressure) | Excellent | 30–80 bar typical, handles coolant contamination well |
| BTA drilling (moderate depth) | Good | Adequate for moderate pressure BTA (50–80 bar) |
| BTA drilling (high pressure) | Poor | Limited to ~100 bar maximum |
| Coolant circulation (chip tank) | Good | Handles high particulate load, continuous duty |
Maintenance Requirements
| Component | Service Life | Maintenance | Indicator of Wear |
|---|
| Stator (elastomer) | 2,000–4,000 hours | Replace when flow drops | Flow decreases, pressure may fluctuate |
| Rotor (hardened steel) | 4,000–8,000 hours | Replace with stator or independently | Wear pattern on surface |
| Universal joint | 2,000–4,000 hours | Lubrication, seal replacement | Noise, vibration |
| Shaft seals | 1,000–3,000 hours | Replace | Leakage at shaft |
Piston Pumps
Types
| Pump Type | Mechanism | Pressure Range | Typical Application |
|---|
| Axial piston (swash plate) | Pistons arranged parallel to shaft, reciprocated by angled plate | 50–350 bar | High-pressure BTA drilling, deep hole gun drilling |
| Radial piston | Pistons arranged radially around eccentric shaft | 100–700 bar | Ultra-high-pressure applications (rare in standard DHD) |
| Bent-axis piston | Pistons arranged at angle to shaft | 100–400 bar | Mobile equipment, some high-pressure DHD systems |
Application in Deep Hole Drilling
| Application | Suitability | Why |
|---|
| Gun drilling (standard) | Good | 50–100 bar, efficient, reliable |
| Gun drilling (deep, > 100×D) | Excellent | 100–200 bar capability — needed for deep holes |
| BTA drilling (standard) | Excellent | 50–150 bar — ideal for BTA pressure requirements |
| BTA drilling (deep, counterpressure) | Excellent | 150–300 bar — counterpressure applications |
| Coolant circulation (chip tank) | Poor | Cannot tolerate particulate contamination |
Maintenance Requirements
| Component | Service Life | Maintenance | Indicator of Wear |
|---|
| Piston and slipper | 2,000–5,000 hours | Replace worn pistons | Pressure drop, increased case drain flow |
| Valve plate | 3,000–6,000 hours | Resurface or replace | Noise, pressure ripple |
| Cylinder block | 4,000–8,000 hours | Replace | Wear at piston bore |
| Shaft seal | 1,000–3,000 hours | Replace | Leakage at shaft |
| Control valve | 2,000–5,000 hours | Clean or replace | Pressure control instability |
Centrifugal Pumps
Operating Principle
| Feature | Description |
|---|
| Mechanism | Impeller rotates inside volute — centrifugal force accelerates fluid, converted to pressure in volute |
| Flow characteristic | Non-positive displacement — flow varies inversely with pressure |
| Self-priming | No (must be primed) |
| Particle handling | Excellent — large clearances tolerate fines and small chips |
Application in Deep Hole Drilling
| Application | Suitability | Why |
|---|
| Primary coolant pump (gun drilling) | Poor — low pressure | Cannot achieve required pressure for gun drilling |
| Primary coolant pump (BTA) | Poor — low pressure | Cannot achieve required pressure for BTA |
| Coolant return pump | Excellent | High flow, low pressure, handles contamination |
| Chip tank circulation | Excellent | Moving large volumes, tolerant of debris |
| Pre-filter / booster pump | Good | Feed pump for high-pressure piston pump |
| Skimmer pump | Excellent | Low pressure, continuous duty |
Selection Criteria
Pressure and Flow Requirements by Drilling Method
| Drilling Method | Hole Diameter | Coolant Pressure | Coolant Flow | Recommended Pump Type |
|---|
| Gun drilling | 3–10 mm | 80–150 bar | 10–40 L/min | Piston pump |
| Gun drilling | 10–30 mm | 50–100 bar | 20–100 L/min | Piston or screw pump |
| Gun drilling | 30–60 mm | 30–80 bar | 40–200 L/min | Screw pump |
| BTA drilling | 20–40 mm | 80–150 bar | 100–300 L/min | Piston pump |
| BTA drilling | 40–80 mm | 50–120 bar | 200–600 L/min | Piston pump (multiple) |
| BTA drilling | 80–200 mm | 30–80 bar | 300–1,500 L/min | Screw or centrifugal (multiple) |
Selection Decision Matrix
| Priority | Screw Pump | Piston Pump | Centrifugal Pump |
|---|
| Highest pressure | No | Best | No |
| Highest flow | No | Moderate | Best |
| Contamination tolerance | Good | Poor | Best |
| Energy efficiency | Good | Best | Moderate |
| Quiet operation | Best | Poor | Good |
| Longest maintenance interval | Moderate | Shorter | Best |
| Lowest initial cost | Moderate | Higher | Lowest |
| Simple installation | Moderate | Complex | Simple |
Installation Considerations
Common Installation Issues
| Issue | Symptom | Root Cause | Corrective Action |
|---|
| Cavitation | Noise, pressure fluctuation | Suction restriction, undersized line, high coolant temperature | Increase suction line diameter, check tank level, reduce temperature |
| Air entrainment | Pressure drops, foaming | Leak on suction side, vortex at tank outlet | Check suction fittings, install baffles, submerge suction |
| Overheating | Oil/coolant temperature > 60°C | Pressure relief valve set too high, excess flow bypassed | Adjust relief valve, check system pressure match |
| Vibration | Noise, pipe movement | Misalignment, loose mounting, worn coupling | Align pump and motor, tighten mounts, replace coupling |
| Seal failure | Leakage at shaft | Dry running, contamination, incorrect seal material | Verify priming, check coolant compatibility, upgrade seal |
Piping and Filtration Requirements
| Pump Type | Suction Line Size | Inlet Filtration | Return Filtration | Pressure Line Filter |
|---|
| Screw pump | 1.5–2× pump inlet | 200–500 µm | 50–100 µm | Optional — 50 µm |
| Piston pump | 1.5–2× pump inlet | 100–200 µm | 25–50 µm | Required — 10–25 µm |
| Centrifugal pump | 2–3× pump inlet | 500–1,000 µm | 100–500 µm | Not typically required |
FAQ
What type of coolant pump is best for deep hole drilling?
Piston pumps (axial piston) are the most common choice for deep hole drilling because they provide the high pressure (50–350 bar) needed for chip evacuation while maintaining good efficiency. Screw pumps (progressive cavity) are a good alternative for moderate pressure applications (30–80 bar) and offer better particle tolerance and quieter operation. Centrifugal pumps are not suitable as primary coolant pumps for deep hole drilling — they cannot achieve the required pressure — but are used for circulation and return.
Why is high coolant pressure needed for deep hole drilling?
High coolant pressure is required to: force coolant through the narrow clearance between the drill and the hole wall (typical clearance is 0.010–0.030 mm per side for gun drilling), overcome the back pressure created by the chip column in the drill flute or chip tube, push chips out of the hole at the same rate they are generated, and maintain velocity sufficient for chip transport. Insufficient pressure causes chip packing, which leads to chip jamming and drill breakage.
What is the difference between a screw pump and a piston pump for coolant?
A screw pump uses a helical rotor turning inside an elastomer stator — it produces continuous, non-pulsating flow and tolerates moderate contamination. A piston pump uses reciprocating pistons — it produces higher pressure with better efficiency but requires clean coolant and produces pressure pulsations. Screw pumps are simpler to maintain but limited to ~100 bar. Piston pumps are more complex but capable of 300+ bar.
How do I select the right coolant pump for my deep hole drilling machine?
Determine required pressure and flow based on drilling method, hole diameter, and depth. For gun drilling under 30 mm diameter: piston pump (50–150 bar). For gun drilling 30–60 mm: screw pump (30–80 bar) or piston pump. For BTA drilling under 80 mm: piston pump (50–150 bar). For large-diameter BTA: multiple pumps or screw/centrifugal combination. Match pump maximum pressure to 120% of required drilling pressure to allow margin for filter clogging.
How often should coolant pump maintenance be performed?
Screw pump: inspect stator every 2,000 hours, replace at 2,000–4,000 hours. Piston pump: check case drain flow every 1,000 hours (increasing flow indicates wear), major overhaul at 3,000–6,000 hours. Centrifugal pump: replace bearings at 5,000–8,000 hours, replace shaft seal at 3,000–5,000 hours. In all cases, follow the pump manufacturer's specific maintenance schedule and monitor trend data (pressure, flow, temperature, noise) to adjust intervals.
The coolant pump is the most power-intensive system on a deep hole drilling machine and the most critical for process reliability. Selecting the right type — piston for high pressure, screw for moderate pressure with contamination tolerance, centrifugal for circulation — and maintaining it properly ensures consistent chip evacuation and hole quality. This article reflects industry practice as of 2026.
