Liquid Chromatography Instruments are commonly used in our labs, with the pump being a crucial component. Learn how to optimize your liquid chromatography usage and perform effective pump maintenance with us.

Degassing Unit

  1. After changing the mobile phase, it is necessary to perform a purge operation to quickly replace the solvent in the tubing and pump head and remove any bubbles generated when different solvents mix. Typically, the degassing unit can effectively remove smaller bubbles through vacuum degassing. However, it may not be very effective for larger bubbles. Therefore, it is advisable to thoroughly degas the mobile phase before it is introduced into the system. Common degassing methods include ultrasonic degassing and helium degassing, among others.
  2. For unused mobile phase channels, it is best to fill them with methanol and ensure that the filter frits are immersed in the solvent. Otherwise, the vacuum level of the degassing unit’s vacuum pump may not be achieved, and the pump may continue to operate, potentially damaging the vacuum pump.
Schematic diagram of degasser
  1. The degassing unit’s degassing membrane is made of a special material that allows gases to pass through but prevents the passage of liquids.
    The standard degassing membrane included with most units is not compatible with non-polar solvents and those containing more than 20% THF (Tetrahydrofuran). If you are using a non-polar mobile phase, it is advisable to bypass the degassing unit to prevent the mobile phase from passing through it. You can do this by directly connecting the mobile phase tubing to the pump head or by replacing the degassing membrane with one compatible with non-polar solvents.

Purge Valve and Proportioning Valve

Purge Valve for Pump Head
  1. When purging a quaternary low-pressure pump, it’s important to degas one channel at a time to ensure thorough degassing and prevent incomplete purging. For binary high-pressure pumps, you can simultaneously open the purge valves for different pump modules.
  2. Set up dedicated channels for the organic phase and the aqueous phase to reduce the occurrence of salt precipitation, which can damage check valves, seals, and plunger rods. Regularly replace the pure water channel to avoid microbial or algae growth due to extended use of a single channel.
  3. In case of blockages in the quaternary proportioning valve, disconnect all the tubing above the proportioning valve, use a syringe to inject an appropriate solvent into the valve, and flush each channel until the liquid flows smoothly. Alternatively, remove the proportioning valve and clean its components with methanol using ultrasonic cleaning if needed.
  4. As a friendly reminder, when using isocratic conditions, try to avoid using the proportioning valve to mix mobile phases. During hot summer days, aim to change to pure water or pure salt solution every half day to prevent potential issues, which many users have encountered.

One-Way Valves

Schematic diagram of one-way valve structure

One-way Valve, Used to Prevent Reverse Flow of Mobile Phase

Symptoms of Failure: Pressure fluctuations, unstable baseline, no pressure.

Causes: Failure to filter the mobile phase or frequent use of high-concentration buffer salt solutions or unfiltered pure acetonitrile can lead to contamination, blockage, or adhesion of the check valve, resulting in unstable pressure or no pressure.

Solution: Remove the check valve housing, take out the valve core, and clean it with an ultrasonic bath using a 5% methanol-water solution.

One-way valve core diagram


  1. When performing ultrasonic cleaning on check valves made of ruby material, ensure that the arrow direction is facing upward. Do not use excessive ultrasonic power, and avoid prolonged ultrasonic exposure to prevent damage to the ruby core of the check valves.
  2. Check valves are directional, allowing the mobile phase to flow in only one direction. During installation, it is crucial to be mindful that installing them in the wrong direction will prevent the flow of the mobile phase into the subsequent working system.

Plunger rod and sealing ring

Component Introduction: Currently, commonly used sealing ring materials in the market include graphite, PTFE (Polytetrafluoroethylene), polyethylene, and other materials. When selecting a sealing ring material, it is essential to choose the appropriate material based on the solvent system being used.

Symptoms of Failure: Leakage alarms, low pressure, pressure fluctuations, increased solvent in the circulating solvent reservoir due to rear seal cleaning.

Causes: Poor sealing due to wear and tear on the plunger rod or sealing ring, resulting in leakage.

Solution: Use a clean soft cloth dipped in an appropriate solvent to clean the plunger rod, and if necessary, replace the plunger rod and sealing ring with new ones.

SealWash Post-Seal Cleaning System

Due to the continuous reciprocating motion of the plunger rod, the use of high-concentration buffer salts with precipitation can cause wear and tear on the sealing ring and plunger rod. Therefore, when using buffer salts, it is essential to clean the plunger rod promptly.

Cleaning Solution: Typically, use 10% methanol or isopropanol, or follow the recommended reagent from the corresponding brand manufacturer. For open SealWash cleaning systems, it’s important to replenish the cleaning solution promptly. For circulating SealWash cleaning systems, the cleaning solution should be replaced regularly.


Mixers are generally categorized into static mixers and dynamic mixers. They are also known to be susceptible to blockages.

Symptoms of Failure: Increased pressure or fluctuations.

Causes: Contamination or blockage of mixers due to impurities in the mobile phase or salt precipitation. In addition to blockages or contamination in the flow path before the mixer, the internal cavity filters of the mixer can also become contaminated or blocked.

Solution: For salt precipitation issues, you can use hot water flushing or disassemble the mixer for ultrasonic cleaning. If the problem cannot be resolved through cleaning, it may be necessary to replace the mixer or tubing.

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