The coolant system is arguably the most important component of a deep hole drilling operation — more critical than the spindle or the controls. Without adequate coolant pressure, flow, and filtration, the process simply does not work. Chips clog, tools break, and holes fail inspection.
Yet the coolant system is often treated as an afterthought in machine purchasing decisions. This guide covers the three main pump technologies, filtration requirements, system configuration options, and total cost considerations.
1. Pump Technology Comparison
Three pump types dominate deep hole drilling coolant delivery: screw spindle pumps, centrifugal pumps, and seal-less diaphragm pumps (Hydra-Cell type). Each has distinct advantages depending on pressure requirements and operating conditions.
Screw Spindle Pumps
Positive displacement three-screw pumps that deliver smooth, constant flow proportional to shaft speed.
| Parameter | Typical Range |
|---|---|
| Maximum pressure | Up to 200 bar (2,900 PSI) |
| Maximum flow | Up to 878 L/min |
| Efficiency | 70–85% |
| Particle tolerance | Requires filtered coolant (< 50 μm) |
| Best for | Primary high-pressure delivery in BTA and gun drilling |
Sources: Brinkmann Pumps screw spindle series; Allweiler EMTEC-C; MMS Online “Three-Screw Pump Optimizes Coolant Delivery.”
Screw spindle pumps are the most common choice for dedicated deep hole drilling machines. They provide the high pressure and flow required for BTA drilling (20–100 bar, 200–400 L/min) and gun drilling (40–150 bar, 40–200 L/min). Their smooth, pulse-free flow is ideal for consistent chip evacuation.
Centrifugal / Multistage Pumps
Closed-impeller centrifugal pumps are limited to medium-pressure applications.
| Parameter | Typical Range |
|---|---|
| Maximum pressure | Up to 50 bar (725 PSI) |
| Maximum flow | Up to 1,000+ L/min (at low pressure) |
| Efficiency | 60–75% |
| Particle tolerance | Higher than screw pumps |
| Best for | Return/transfer duties, low-pressure systems |
Source: Brinkmann Pumps medium-pressure series.
Centrifugal pumps are not suitable as primary high-pressure pumps for deep hole drilling (MMS Online; Allweiler). They are commonly used as return pumps to move coolant from collection sumps back through filtration, or for low-pressure applications below 50 bar.
Seal-less Diaphragm Pumps (Hydra-Cell)
Positive displacement pumps with a unique seal-less design that handles abrasive particles without damage.
| Parameter | Typical Range |
|---|---|
| Maximum pressure | Up to 2,500 PSI (172 bar) |
| Maximum flow | Up to 140 L/min (37 GPM) |
| Efficiency | 78–90% (constant across pressure range) |
| Particle tolerance | Up to 500 microns — no fine filtration needed |
| Best for | Energy-sensitive applications, abrasive coolants |
Source: Hydra-Cell Machine Tool Coolant brochure; Wanner Pumps.
Energy comparison data (Hydra-Cell published):
| Condition | Screw Pump | Hydra-Cell | Savings |
|---|---|---|---|
| 1.06 GPM @ 1,160 PSI | 2.8 kW | 0.7 kW | 147% less energy |
| 7.66 GPM @ 580 PSI | 5.6 kW (centrifugal) | 2.5 kW | 122% less energy |
The seal-less design also means these pumps can handle dirty coolant with particles up to 500 microns, potentially eliminating the need for fine filtration — a significant cost saving in both equipment and maintenance.
Pump Selection Matrix
| Requirement | Screw Spindle | Centrifugal | Hydra-Cell (Diaphragm) |
|---|---|---|---|
| High pressure (> 50 bar) | ✅ | ❌ | ✅ |
| Very high flow (> 400 L/min) | ✅ | ✅ | ❌ |
| Energy efficiency | Moderate | Low | Best |
| Handles dirty coolant | ❌ | Moderate | Best (500 μm) |
| Smooth, pulse-free flow | ✅ | ❌ | Moderate |
| Initial cost | Moderate | Low | Higher |
| Maintenance cost | Moderate | Low | Low |
Sources: Brinkmann; Hydra-Cell; Allweiler.
2. Filtration Requirements
Micron Rating by Operation
| Operation | Required Filtration | Filter Type |
|---|---|---|
| Gun drilling (≤ 0.125“ / 3 mm) | < 15 μm | Cartridge or paper band |
| Gun drilling (standard) | < 20 μm | Paper band + cartridge |
| BTA drilling | < 20 μm | Magnetic + paper band |
| Honing / lapping / superfinishing | < 10 μm | Cartridge (high efficiency) |
| Skiving & roller burnishing | < 10 μm | Cartridge or candle filter |
Sources: Rosedale Products coolant filter selection guide; Lex Technoaid deep drilling case study; Hydac Flexmicron filter specifications.
A multi-stage filtration system is recommended for production environments (Lex Technoaid case study):
| Stage | Type | Target Removal |
|---|---|---|
| 1 | Magnetic separator | Ferrous particles > 50 μm |
| 2 | Paper band filter | Particles > 20–30 μm |
| 3 | Cartridge filter | Particles > 5–10 μm |
This configuration delivers approximately 5–10 μm final filtration, sufficient for gun drilling and BTA operations. The case study showed this level of filtration enabled drilling and finishing in a single pass without secondary operations.
Filter Pressure Drop Consideration
Finer filtration increases pressure drop, which must be accounted for in pump sizing. Hydac data shows:
| Filter Rating | Resistance Factor (water-based) |
|---|---|
| 5 μm | 42 |
| 10 μm | 15 |
| 20 μm | 8 |
A 5 μm filter has 2.8× the resistance of a 10 μm filter. If your pump is sized for a 20 μm filter, switching to 5 μm without adjusting the pump will reduce flow. See the Coolant Pressure and Flow Rate Guide for pump sizing calculations.
3. Centralized vs. Standalone Systems
Comparison
| Factor | Centralized System | Standalone (Per Machine) |
|---|---|---|
| Initial cost (multi-machine) | Higher ($50k–$150k) | Lower ($10k–$40k per machine) |
| Floor space | Better (shared footprint) | Higher (individual units) |
| Maintenance | Single point | Multiple points |
| Flexibility | Low (system designed for fixed capacity) | High (each machine independent) |
| Temperature control | Easier (single chiller) | Requires individual chillers |
| Risk | Single point of failure affects all machines | Failure isolated to one machine |
Source: Lex Technoaid centralized system case study; industry practice.
A documented case study connected four deep drilling machines to a single centralized system with magnetic conveyors, band filters, cartridge filters, and temperature management. The result was reduced floor space compared to separate units for each machine (Lex Technoaid).
For shops with 3+ deep hole drilling machines, centralized systems are worth evaluating. For a single machine, standalone is the standard approach.
4. Coolant Temperature Control
Deep hole drilling generates significant heat — a 30 kW coolant pump running continuously adds approximately 25,000 kcal/h to the coolant. Without temperature control, coolant temperature can rise above 50°C, which:
- Reduces viscosity, decreasing chip transport capability
- Accelerates additive depletion in oil-based coolants
- Promotes bacterial growth in water-miscible emulsions
- Causes thermal expansion in the machine, affecting accuracy
Chiller Sizing
| Machine Type | Recommended Chiller Capacity | Typical Coolant Temperature |
|---|---|---|
| Small gun drill | 5–10 kW | 25–35°C |
| Medium BTA (60 mm cap.) | 15–25 kW | 25–40°C |
| Large BTA (150 mm cap.) | 30–50 kW | 25–40°C |
| Centralized system (4+ machines) | 50–100+ kW | 25–35°C |
The optimal coolant temperature range for deep hole drilling is 25–40°C at the tool interface.
5. Total Cost Considerations
System Cost Estimates
| Component | Small System (single gun drill) | Large System (BTA + central) |
|---|---|---|
| High-pressure pump | $5,000–$15,000 | $15,000–$40,000 |
| Return/transfer pump | $1,000–$3,000 | $3,000–$8,000 |
| Filtration (multi-stage) | $3,000–$10,000 | $15,000–$50,000 |
| Coolant tank (500–2,000 L) | $2,000–$5,000 | $5,000–$15,000 |
| Chiller / heat exchanger | $3,000–$8,000 | $10,000–$30,000 |
| Piping, valves, installation | $3,000–$8,000 | $10,000–$30,000 |
| Total system cost | $17,000–$49,000 | $58,000–$173,000 |
Sources: Industry estimates based on Brinkmann, Hydra-Cell, and Wanner pricing.
Annual Operating Cost Comparison
Using the energy data from Section 1 for a pump running 2,000 hours/year at $0.15/kWh:
| Pump Type | Power (at 7.66 GPM, 580 PSI) | Annual Energy Cost |
|---|---|---|
| Centrifugal | 5.6 kW | $1,680 |
| Hydra-Cell | 2.5 kW | $750 |
| Annual savings with Hydra-Cell | — | $930 |
At higher pressures (1,000+ PSI), the savings are proportionally larger. For the full TCO picture, see the Total Cost of Ownership Guide.
6. Selection Decision Matrix
| If you need… | Recommended Pump | Recommended Filtration |
|---|---|---|
| High pressure (100–200 bar), high flow | Screw spindle (Brinkmann, Allweiler) | 20 μm magnetic + band + 10 μm cartridge |
| Medium pressure (40–100 bar) | Screw spindle or Hydra-Cell | 20 μm band + 10 μm cartridge |
| Energy efficiency priority | Hydra-Cell | Standard (pump tolerates dirty coolant) |
| Dirty coolant / high particle load | Hydra-Cell (500 μm tolerance) | Coarse only (20–50 μm) |
| Low-pressure return / transfer | Centrifugal | 50 μm or coarser |
| Single machine | Standalone system | As above |
| 3+ machines | Evaluate centralized | Multi-stage central |
7. Pre-Purchase Checklist
| Check | Item |
|---|---|
| □ | Pump type matches pressure and flow requirements |
| □ | Pump can handle target filtration level (pressure drop) |
| □ | Filtration system meets < 20 μm for gun drilling / < 10 μm for precision |
| □ | Coolant tank sized for minimum 5× pump flow per minute |
| □ | Chiller capacity adequate for connected load |
| □ | Piping sized for minimum 3 m/s flow velocity |
| □ | Hose whip restraints on all high-pressure connections |
| □ | Pressure relief valve installed and set correctly |
| □ | Safety interlocks on access doors near high-pressure lines |
For coolant system safety requirements, refer to the Deep Hole Drilling Safety Guide.
Summary
| Pump Type | Pressure Range | Flow Range | Best Application | Energy Efficiency |
|---|---|---|---|---|
| Screw spindle | Up to 200 bar | Up to 878 L/min | Primary DHD coolant delivery | Moderate |
| Centrifugal | Up to 50 bar | Up to 1,000+ L/min | Return/transfer, low-pressure | Low |
| Hydra-Cell (seal-less) | Up to 2,500 PSI | Up to 140 L/min | Energy-sensitive, abrasive coolant | Best |
- Gun drilling requires < 15–20 μm filtration and 40–150 bar
- BTA drilling requires < 20 μm filtration and 20–100 bar
- Multi-stage filtration (magnetic + band + cartridge) is recommended for production
- Screw spindle pumps are the standard for dedicated DHD machines
- Hydra-Cell pumps offer significant energy savings and can handle dirty coolant
Key Sources
- Brinkmann Pumps, “Machine Tool Coolant Supply — Medium and High Pressure Pumps” — pump specifications
- MMS Online, “Three-Screw Pump Optimizes Coolant Delivery” — screw pump vs centrifugal comparison
- Allweiler EMTEC-C, “Raising the Performance Bar for Machine Tool Coolant” — three-screw pump advantages
- Hydra-Cell / Wanner Pumps, “Machine Tool Coolant” brochure — energy comparison data and seal-less design
- Rosedale Products, “Coolant Filter Selection Guide” — micron ratings by operation type
- Lex Technoaid, “Single Process Deep Drilling Enabled by Advanced Coolant Filtration” — multi-stage filtration case study
- Hydac, “Flexmicron Standard Filter Elements” — resistance factors for micron ratings