The compression values of the pump heads can provide valuable information for troubleshooting.

When

You observe pressure pulsation or shifts in retention time.

Follow these steps

  1. In the Chromeleon software, check the Compression value for the pump heads (= CompressionDrv1).

    The values indicate the compression of the last stroke in percent. The compression value should be less than 100%.

    • With isocratic conditions, the compression value should remain stable.

    • When running a gradient, the compression value changes roughly proportional to the pressure curve.

    If the value is close to 100%, the required precompression may not be reached and pulsation may occur.

    The table shows guide values for some solvents (pure solvent, degassed, delivered at 40 MPa) with the pump being purged and the pressure being stable for some time. In a range between 30 MPa and 60 MPa the values can be considered as linear to the pressure.

Solvent

Compression in %

Water

25 % ± 10 %

Methanol

50 % ± 10 %

Acetonitrile

45 % ± 10 %

  1. Take remedial action if required.

Compression

Remedial Action

Lower than indicated in the table

The outlet check valve may be defective. Replace the valve cartridge. See Replacing the Outlet Check Valves.

Higher than indicated in the table

Very high (message "Compression limit reached" and low pressure)

  • Air bubbles may be present in the pump. Make sure that no air bubbles are present in the solvent lines and purge the pump.

  • If solvent shut-off valves are installed: Verify that the valves are open.

  • Excessive leakage may be present on the inlet check valve. Remove the solvent line from the solvent reservoir and the solvent line filter from the solvent line. While the pump is running, observe the liquid in the solvent line. If the liquid moves also against the direction of flow during the stroke, the inlet check valve may be defective. Replace the valve cartridge. See Replacing the Inlet Check Valves.