Coolant pressure pulsations from piston pumps travel through the system and directly into the drilling process. Each pressure pulse causes a tiny variation in chip load — producing chatter marks, inconsistent surface finish, and vibration that accelerates drill wear. An accumulator or pulsation damper smooths these pulsations, delivering steady coolant flow to the drill.
Accumulator Types
Type Comparison
| Accumulator Type | Pressure Range | Volume Range | Response Time | Best Application |
|---|
| Bladder accumulator | 10–200 bar | 0.5–50 L | Fast | Most common — general purpose pulsation damping |
| Diaphragm accumulator | 5–100 bar | 0.1–10 L | Fast | Small systems, compact installations |
| Piston accumulator | 20–350 bar | 1–200 L | Moderate | High-pressure, large volume |
| Spring-loaded | 1–20 bar | 0.1–5 L | Moderate | Low-pressure damping |
| Inline pulsation damper | 10–100 bar | 0.1–2 L | Very fast | Direct pump outlet mounting |
Bladder Accumulator Details
| Component | Function | Material |
|---|
| Shell (pressure vessel) | Contains gas and fluid under pressure | Carbon steel or stainless steel |
| Bladder | Separates gas from fluid | NBR (Nitrile), FKM (Viton), or EPDM |
| Gas valve | Charges the bladder with nitrogen | Brass or steel — Schrader or tire type |
| Fluid port | Connects to coolant system | Threaded NPT or BSP |
| Poppet valve | Prevents bladder extrusion into fluid port | Stainless steel |
Functions in Coolant Systems
Primary Functions
| Function | Description | Benefit to Drilling |
|---|
| Pulsation damping | Absorbs pressure spikes from piston pumps | Smooth coolant flow — no chatter marks |
| Pressure holding | Maintains pressure when pump is off | Prevents drill backflow, keeps system primed |
| Thermal expansion absorption | Absorbs coolant volume increase from heating | Prevents pressure rise from thermal expansion |
| Shock absorption | Absorbs pressure spikes from valve closure | Prevents hose and seal damage |
| Emergency pressure reserve | Provides coolant pressure if pump stops | Short-term pressure to retract drill |
Pulsation Damping Specifics
| Pump Type | Pulse Frequency | Pulse Amplitude (without damper) | Required Damping | Typical Accumulator Size |
|---|
| 3-plunger piston pump | 15–50 Hz | 5–15% of mean pressure | Low — moderate | 0.5–2 L per 10 L/min flow |
| 5-plunger piston pump | 25–80 Hz | 2–8% of mean pressure | Low | 0.3–1 L per 10 L/min flow |
| Single-acting piston pump | 5–15 Hz | 20–50% of mean pressure | High | 2–5 L per 10 L/min flow |
| Progressive cavity pump | Smooth | < 2% | Minimal | None needed typically |
| Centrifugal pump | Smooth | < 1% | None | Not needed |
Sizing Guidelines
Accumulator Volume Selection
| Flow Rate (L/min) | Pressure (bar) | Recommended Accumulator Volume | Pulsation Reduction |
|---|
| < 50 | 20–50 | 0.5–1 L | 80–90% |
| 50–100 | 20–50 | 1–2 L | 80–90% |
| 100–200 | 20–50 | 2–4 L | 80–90% |
| 50–100 | 50–100 | 1–3 L | 80–90% |
| 100–200 | 50–100 | 3–6 L | 80–90% |
| 200–500 | 50–100 | 6–15 L | 80–90% |
| > 500 | > 100 | 15–50 L | 80–90% |
| Application | Sizing Rule | Notes |
|---|
| Pulsation damping | V = (0.5–1.5) × (pump flow L/min) / (operating pressure bar) | Larger for lower pressure |
| Pressure holding | V = required volume to maintain pressure during pump-off period | Calculate from leak rate × time |
| Thermal expansion | V = coolant volume increase from temperature rise | Typically 1–2% of total system volume |
| Emergency reserve | V = volume needed to retract drill | Calculate from cylinder volume |
Precharge Pressure
Precharge Guidelines
| Function | Precharge Pressure | Why |
|---|
| Pulsation damping | 60–70% of mean operating pressure | Bladder must compress and expand with each pulse |
| Pressure holding | 70–90% of minimum system pressure | Keeps bladder compressed at all times |
| Thermal expansion | 80–90% of system pressure at ambient temperature | Absorbs expanding coolant |
| Shock absorption | 50–60% of system pressure | Allows maximum fluid acceptance |
Precharge Checking Procedure
| Step | Action | Detail |
|---|
| 1 | Depressurize coolant system | Verify zero pressure at accumulator |
| 2 | Close isolation valve between accumulator and system | If equipped |
| 3 | Remove protective cap from gas valve | — |
| 4 | Connect nitrogen gauge / charger to gas valve | — |
| 5 | Read current precharge pressure | — |
| 6 | Compare to required precharge (60–70% of operating pressure) | — |
| 7 | If pressure is low — add nitrogen | Use nitrogen bottle with regulator |
| 8 | If pressure is high — bleed nitrogen | Press Schrader valve stem |
| 9 | Adjust to correct pressure | ± 0.5 bar tolerance |
| 10 | Remove gauge — replace cap | — |
| 11 | Open isolation valve | — |
| 12 | Re-pressurize system | Check for leaks |
Precharge Frequency
| Condition | Precharge Check Frequency |
|---|
| New accumulator | Monthly for first 3 months |
| Normal operation | Quarterly |
| System with pressure fluctuation | Monthly |
| After any system pressure change | Immediately |
| Annual preventive maintenance | At minimum |
Installation
Placement Guidelines
| Guideline | Reason | Implementation |
|---|
| Mount as close to pulsation source as possible | Maximum damping effectiveness | Within 1 m of pump outlet |
| Mount vertically (bladder type) | Bladder operates correctly | Bladder valve at top — fluid port at bottom |
| Use rigid piping to accumulator | Flexible hose reduces damping effectiveness | Steel pipe — not hose |
| Install isolation valve | Allows precharge check without system drain | Ball valve between system and accumulator |
| Support accumulator weight | Heavy accumulator stresses piping | Bracket or support stand |
| Protect from heat, debris | Extends bladder life | Keep away from heat sources — cover if needed |
Typical System Layout
| Component Order | Location | Purpose |
|---|
| Coolant pump | Pump outlet | Pressure source |
| Check valve | After pump | Prevents backflow through pump |
| Accumulator (pulsation damper) | After check valve — close to pump | Dampens pump pulsations |
| Pressure gauge | After accumulator | Measures smoothed pressure |
| Relief valve | After gauge | Overpressure protection |
| Filter | Before drill | Final filtration |
| Flow control valve | At machine | Drilling flow control |
| Drill | Spindle | Process |
Troubleshooting
| Symptom | Likely Cause | Corrective Action |
|---|
| Pressure fluctuation at drill | Precharge pressure incorrect | Check and adjust precharge |
| Accumulator undersized | Increase accumulator volume |
| Bladder failed (ruptured) | Replace bladder |
| No accumulator in system | Install accumulator |
| Chatter marks on bore surface | Pulsation reaching drill | Check accumulator function — increase damping |
| Accumulator makes knocking sound | Poppet valve or bladder hitting end caps | Check precharge — bladder damaged |
| System pressure drops when pump stops | Accumulator holding pressure but leak elsewhere | Check system for leaks |
| No pressure fluctuation reduction after installation | Accumulator valve closed | Open isolation valve |
| Precharge pressure wrong | Adjust to 60–70% of operating pressure |
| Bladder fails repeatedly | Precharge too low — bladder contacts poppet | Adjust precharge — check gas valve |
| Incompatible bladder material | Verify compatibility with coolant |
| Temperature too high | Cool coolant or upgrade bladder material |
Maintenance
| Task | Frequency | Benefit |
|---|
| Check precharge pressure | Quarterly | Maintains damping effectiveness |
| Inspect for external leaks | Monthly | Detects seal failure |
| Listen for knocking | Monthly | Detects bladder or poppet problems |
| Check gas valve for leaks | Quarterly | Prevents gradual precharge loss |
| Inspect mounting and piping | Annually | Prevents fatigue failure |
| Replace bladder | Every 3–5 years | Prevents unexpected failure |
| Hydrostatic test (pressure vessel) | Per local regulations (typically 5–10 years) | Safety |
FAQ
What does a coolant accumulator do on a deep hole drilling machine?
A coolant accumulator smooths pressure pulsations from the pump — especially piston pumps that produce pressure peaks with each plunger stroke. Without an accumulator, these pressure pulses travel to the drill, causing chatter marks, inconsistent chip breakage, diameter variation, and vibration that accelerates drill wear. The accumulator absorbs the pulse energy by compressing its nitrogen gas charge, releasing the energy between pulses to maintain steady pressure.
How do I set the precharge pressure on a coolant accumulator?
Depressurize the coolant system and close the isolation valve to the accumulator. Connect a nitrogen gauge/charger to the gas valve on the accumulator. Read the current precharge. Adjust to 60–70% of the mean operating pressure for pulsation damping. For example, if the system operates at 100 bar, set the precharge to 60–70 bar. Use dry nitrogen only — never oxygen or compressed air (oxygen in the bladder causes explosive failure if oil enters).
How do I know if my accumulator is working correctly?
Check the pressure gauge — with a functioning accumulator, the gauge needle should be steady. A fluctuating needle indicates inadequate damping. Listen for knocking sounds from the accumulator — this indicates the bladder is bottoming out (precharge too low) or the poppet valve is damaged. Measure precharge pressure quarterly — a gradual loss indicates a leak in the gas valve or bladder. If the accumulator is not reducing pressure fluctuation, check precharge first.
What size accumulator do I need for my coolant pump?
For pulsation damping, use 0.5–2 L of accumulator volume per 10 L/min of pump flow. A 100 L/min piston pump typically needs a 5–10 L accumulator. The higher the operating pressure, the smaller the accumulator needed (gas compresses more at higher pressure). If the accumulator is undersized, it cannot absorb the full pulse volume and pressure fluctuation remains. Oversizing is not harmful — it provides better damping and a safety margin.
Why does my accumulator bladder keep failing?
Common causes: incorrect precharge pressure (too low — bladder hits the poppet valve on each cycle and wears through), incompatible bladder material (coolant chemistry attacks the bladder — verify material compatibility), temperature too high (coolant above 60°C degrades the bladder), or gas valve leak (gradual precharge loss causes the same problem as low precharge). Replace the bladder with the correct material, verify precharge is set to 60–70% of operating pressure, and maintain coolant temperature below 50°C.
An accumulator is a simple device that makes a significant difference in deep hole drilling coolant performance. It smooths pump pulsations that would otherwise cause chatter marks, surface finish variation, and drill vibration. Size the accumulator correctly, set precharge to 60–70% of operating pressure, check precharge quarterly, and install it as close to the pump outlet as possible. Steady coolant pressure means consistent hole quality. This article reflects industry practice as of 2026.
