HPLC Pump Care and Troubleshooting

Common Technical Support Topics for Continuous Process Pumps

Many inquiries to Chrom Tech relate to care and troubleshooting of our continuous process pumps. Common issues include:

• Erratic flow rates
• No flow from the outlet check valve
• Pressure fluctuation
• Fluid leakage in the pump

Possible Causes

These problems can stem from:

• Bubbles in the pump’s check valve, dirty check valves, or faulty check valves
• Leaks from worn piston seals or scratched pistons
• HPLC fittings that are not properly tightened

Other potential causes include improperly degassed solvents, unfiltered mobile phases, plugged inlet solvent filters, incorrectly plumbed fittings, or particulates from worn piston seals caught in check valves.

Preventing Bubbles in Your HPLC Pump

Proper solvent preparation prevents many pumping problems, including bubble formation which affects flow consistency. Bubbles primarily arise from solvent out-gassing or cavitation.

Solvent Out-Gassing and Sparging

Mobile phases contain dissolved atmospheric gases, mainly N2 and O2, which can form bubbles. Degassing is essential, with helium sparging being the most effective method. Helium removes other dissolved gases efficiently.

Vigorously sparge solvents for 10–15 minutes before use, and maintain a low-pressure helium blanket (2–3 psi) during use. Solvent mixtures with water and organics (methanol, acetonitrile) require sparging to reduce dissolved gases.

Even with sparging, some out-gassing may occur. Installing a back-pressure regulator after the detector flow cell helps prevent bubble formation and baseline noise.

Cavitation

Cavitation occurs when inlet restrictions form vapor bubbles during the inlet stroke. Causes include crimped tubing, plugged inlet filters, tubing over 48" (120 cm) or <0.085" (2 mm) ID, and solvent reservoirs below the pump. Optimal reservoir placement is at or slightly above the pump level.

Viscosity Considerations

Viscous solvents may require increased inlet head pressure. Raising the reservoir above the pump and using helium sparging improves pump performance for high-viscosity fluids.

Filtration

Always filter solvents with a 0.5-micron filter to protect piston seals and check valves. For buffers or salts that precipitate, filter more frequently and store solvents in closed, particle-free containers.

Solvents to Avoid

All Chrom Tech pump wetted parts (except PEEK pump heads) are stainless steel, ceramic, sapphire, ruby, or fluoropolymers. Avoid acids (e.g., hydrochloric acid), solvents like chloroform or carbon tetrachloride, and ammonium hydroxide which may damage pump components over time.

Gravity Placement of Mobile Phase Reservoirs

Place reservoirs at the same level or slightly above the pump. Keep inlet tubing short to minimize pressure loss and bubble formation, particularly with high vapor pressure solvents. Always degas, filter, and cover mobile phases.

Self-Flush Mechanism for Piston Seal Life

Self-flushing pump heads continuously wash the piston surface, preventing salt deposits and abrasion. This is especially important when pumping buffers, acids/bases, or volatile solvents like THF or acetone. Use flush solutions of 100% IPA, 100% methanol, or 20% IPA/methanol-water mixtures; never use water alone.

Recommended Self-Flush Use

• Essential for pumping near-saturated buffers, acids, or bases.
• Prevents crystal formation that can damage the piston seal.
• Required for volatile solvents to avoid drying and seal degradation.

Routine Maintenance

Replacing the Inlet Filter

Check inlet filters periodically. Clogged filters can cause cavitation and flow loss. Prevent microbial growth by using 10–20% organic solvent or growth inhibitors, especially when pumping 100% water or aqueous solutions. Always use filtered, HPLC-grade solvents.

Replacing Pump Piston Seals

Low pressure, pressure fluctuations, or leaks may indicate piston seal issues. Replacement is often required after ~1,000 hours, depending on the fluid.

Cleaning the Piston

Use a folded scouring pad to gently scrub along the length of the piston, rotating frequently. Wipe with a lint-free cloth dampened with alcohol. Avoid perpendicular pressure to prevent damage.

Cleaning Check Valves

1. Remove pump head and immerse in an ultrasonic cleaner with standard cleaning solution for ~30 minutes.
2. Rinse thoroughly with distilled water.
3. Replace pump head assembly.
4. Run pump at 1 mL/min with distilled water for 15 minutes; direct output to waste.

If performance is not restored, replace check valves.

Flushing Continuous Process Pumps

1. Prepare solvents: 100% IPA, 100% distilled water, 20% nitric acid/water (for stainless steel paths).
2. Direct pump outlet to waste.
3. Set pump to maximum flow or press PRIME (P) button.
4. Pump 100% IPA for 3 minutes.
5. Pump 100% distilled water for 3 minutes.
6. For stainless steel paths only: pump 20% nitric acid/water for 3 minutes.
7. Flush with 100% distilled water for at least 3 minutes.
8. Pump 100% IPA for 3 minutes.

The pump is now ready for operation or short/long-term shutdown.

Conclusion

Most high-pressure dosing pump issues relate to check valves, piston seals, and fitting connections. Proper solvent degassing and routine maintenance—including changing inlet filters, check valves, and piston seals—ensure trouble-free HPLC pump performance.

Chrom Tech offers HPLC accessories and replacement parts, including Idex fittings, PEEK tubing, and 316 stainless steel tubing. As an authorized Agilent distributor, we provide Agilent replacement parts for HPLC and GC. For Alltech pumps, contact Chrom Tech for check valves, pistons, and seals.