A deep hole drilling coolant system operates at pressures that would burst a standard shop air line. Every hose, fitting, seal, and connection must be verified to contain the operating pressure before the system is put into service. A pressure test is not optional — it is a safety and process control requirement.
Pressure Test Types
Test Methods
| Test Type | What It Verifies | When to Use | Duration | Pressure Level |
|---|
| Static pressure test | System integrity — no leaks | After maintenance, new installation | 10–30 minutes | 1.5× operating pressure |
| Dynamic pressure test | System performance under flow | Routine verification | During drilling cycle | Operating pressure |
| Flow test | Pump capacity, circuit restriction | Performance complaint | 5–10 minutes | Operating pressure |
| Burst test | Hose and component strength | Qualification only (destructive) | Seconds | 4× operating pressure |
| Drop test | Pressure retention | Leak location | 5–15 minutes | Operating pressure |
Selection Guide
| Situation | Recommended Test | Acceptance Criteria |
|---|
| New machine installation | Static test at 1.5× max operating pressure | No drop in 30 minutes |
| After hose replacement | Static test at 1.5× operating pressure | No drop in 10 minutes |
| After pump repair | Dynamic test — verify pressure and flow | Pressure within spec, flow within 10% |
| Annual system verification | Static + dynamic test | Both pass |
| Suspected leak | Static drop test | Identify and fix all leaks |
| Coolant pressure low | Flow test — check pump output | Flow ≥ 90% of rated |
Test Equipment
Required Equipment
| Equipment | Specification | Purpose |
|---|
| Pressure gauge | Range 0–300 bar, accuracy ±1% | System pressure monitoring |
| Pressure test pump | Manual or powered, to 1.5× system max | Pressurizing the system |
| Flow meter | Range 0–200 L/min (or system rating) | Flow measurement |
| Temperature gauge | Range 0–100°C | Coolant temperature monitoring |
| Relief valve | Set at test pressure + 10% | Safety — prevents over-pressurization |
| Test hoses and adapters | Rated for test pressure | Connecting test equipment |
| Leak detection spray | Non-corrosive | Identifying leak points |
| Data recording form | Per documentation requirements | Recording results |
Safety Precautions
| Precaution | Reason | Implementation |
|---|
| Depressurize before connecting | Prevent injury from pressurized fluid | Bleed all pressure before touching connections |
| Use rated components only | Components below pressure rating can burst | Verify pressure rating on all hoses, gauges, valves |
| Shield high-pressure connections | Contain spray if fitting fails | Use blast shield or face shield |
| Clear area of non-essential personnel | Reduce injury risk | Rope off test area |
| Increase pressure gradually | Allow time to detect leaks at lower pressure | Apply in 25% increments |
| Wear PPE | Protect against fluid injection | Face shield, gloves, apron |
Static Pressure Test Procedure
| Step | Action | Detail |
|---|
| 1 | Isolate the system to be tested | Close block valves, disconnect non-test sections |
| 2 | Install pressure gauge and relief valve | At accessible point in the test circuit |
| 3 | Fill system with coolant | Purge air from high points |
| 4 | Pressurize to 25% of test pressure | Check for major leaks |
| 5 | Pressurize to 50% of test pressure | Inspect all connections |
| 6 | Pressurize to 75% of test pressure | Inspect hoses for ballooning |
| 7 | Pressurize to 100% of test pressure (1.5× operating) | Full test pressure |
| 8 | Hold test pressure | 10–30 minutes per requirement |
| 9 | Monitor pressure gauge | Record pressure at 1-minute intervals |
| 10 | Inspect all connections during hold | Use leak detection spray |
| 11 | Release pressure | Open relief valve slowly |
| 12 | Document results | Pass/fail, pressure readings, leaks found |
Acceptance Criteria
| System Pressure | Test Pressure (1.5×) | Maximum Pressure Drop (30 min) | Maximum Drop (10 min) |
|---|
| 50 bar | 75 bar | 1.5 bar | 0.5 bar |
| 100 bar | 150 bar | 3.0 bar | 1.0 bar |
| 150 bar | 225 bar | 4.5 bar | 1.5 bar |
| 200 bar | 300 bar | 6.0 bar | 2.0 bar |
| 250 bar | 375 bar | 7.5 bar | 2.5 bar |
Dynamic Pressure Test Procedure
| Step | Action | Detail |
|---|
| 1 | Set up machine for normal drilling cycle | Without part (coolant-only cycle) |
| 2 | Install flow meter in supply line | At pump discharge |
| 3 | Start coolant pump | Verify normal startup |
| 4 | Record supply pressure | At gauge nearest the spindle |
| 5 | Record flow rate | At normal operating conditions |
| 6 | Open coolant at the spindle (simulate drilling) | With appropriate restrictor or nozzle |
| 7 | Record pressure with flow | Dynamic pressure reading |
| 8 | Record return pressure | At tank return line |
| 9 | Compare to baseline | Pressure and flow within 10% of baseline |
| 10 | Document results | — |
Leak Location Methods
| Method | Sensitivity | Best For | Equipment |
|---|
| Visual inspection | Moderate — visible leaks | Large leaks, spray | Flashlight, mirror |
| Leak detection spray | Good — bubbles at leak point | Small leaks at fittings | Spray bottle |
| Dye addition | Very good — visible under UV | Pin-hole leaks, multiple leaks | UV dye + UV light |
| Pressure drop test | Good — quantifies total leak | System integrity check | Pressure gauge |
| Ultrasonic detection | Excellent — hears leak noise | High-pressure gas, small leaks | Ultrasonic detector |
| Soap and water | Good at low pressure | Air leaks, low-pressure coolant | Spray bottle |
Documentation
Pressure Test Report
| Field | Example |
|---|
| Machine ID | DHD-003 |
| System tested | Coolant supply — main pump to spindle |
| Operating pressure | 150 bar |
| Test pressure | 225 bar |
| Test type | Static |
| Test date | 2026-06-05 |
| Test duration | 30 minutes |
| Initial pressure | 225.0 bar |
| Final pressure | 223.5 bar |
| Pressure drop | 1.5 bar (0.67%) |
| Leaks found | 2 (both at ORFS fittings, O-rings replaced) |
| Acceptance | Pass (after repair) |
| Tester | T. Wilson |
FAQ
How often should I pressure test the coolant system?
Pressure test the coolant system: annually as part of the preventive maintenance schedule, after any hose or fitting replacement, after any pump or seal repair, after any crash or impact that may have damaged coolant lines, and when a new machine is installed. Between full pressure tests, do a quick dynamic pressure check weekly by verifying operating pressure during a drilling cycle.
What pressure should I use for a coolant system pressure test?
Use 1.5× the maximum operating pressure of the system. If the system operates at 150 bar, test at 225 bar. This provides a safety margin that reveals weak components before they fail in service. Never test above the rated pressure of the lowest-rated component in the system — verify all component ratings before testing.
How do I find a small leak in a high-pressure coolant system?
The most effective method for finding small leaks is a combination of: static pressure test (pressurize to 1.5× operating, observe pressure drop — any drop indicates a leak), leak detection spray (apply to all fittings, connections, and hose ends — bubbles reveal the leak), and UV dye (add UV dye to coolant, run system, inspect with UV light). For very small leaks, ultrasonic detection can locate the high-frequency sound of escaping fluid.
What is the difference between static and dynamic pressure testing?
Static pressure testing pressurizes the system to 1.5× operating pressure with no flow — it verifies the integrity of the system at rest and reveals leaks at connections and seals. Dynamic pressure testing measures pressure and flow during operation — it verifies that the pump can deliver rated pressure and flow under actual operating conditions. Both are needed for complete system verification.
What safety precautions are required for high-pressure coolant testing?
Required precautions: verify all test components are rated for the test pressure, install a pressure relief valve set at test pressure + 10%, shield high-pressure connections from operator exposure, clear the area of non-essential personnel, increase pressure gradually in 25% increments, inspect at each increment before proceeding, and wear appropriate PPE (face shield, chemical-resistant gloves, apron, steel-toed boots). Never use compressed air for pressure testing coolant systems — air stores much more energy than liquid.
Coolant system pressure testing is a safety-critical maintenance procedure. A thorough pressure test before starting production or after maintenance prevents coolant injection injuries and unplanned downtime. This article reflects industry practice as of 2026.
