Backflushing the needle seat of the Agilent Vialsampler

Document created by mschuett Employee on Sep 8, 2020Last modified by mschuett Employee on Oct 8, 2020
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Agilent Support Insights


This Information Applies To: Agilent Infinity II Vialsamplers.



High pressure in the Vialsampler is oftentimes due to a blockage in the needle seat assembly. Sample particulates or plugs from the vial caps can be picked up by the needle when the Vialsampler is drawing the sample. When the valves switches back to mainpass, they are forced into the seat capillary and cause obstruction and high pressure.


Steps to follow: 

To backflush the needle seat:

  1. Turn on the pump flow rate to 3 mL/min through your CDS Software, Lab Advisor or through the Instant Pilot and open the purge valve. Set the injector to bypass mode.
  2. Using Lab Advisor (downloadable by copy-pasting to a new browser tab or window), go to the "Service and Diagnostics" section, highlight the Vialsampler, and choose "Injector Steps". Next, click "Needle up" for the Vialsampler to lift the needle (see Picture 1) up fully.
    Lab Advisor Injector Steps for Seat Backflush 1 - Agilent
    Picture 1: Lab Advisor Injector Steps - Needle Up.
  3. Remove the safety cover (see Picture 2), then lift up and flip the wash port to the left into the service position (Picture 3).
    Open Vialsampler Safety Cover - Agilent
    Picture 2: Removal of the safety cover.

    Wash Port Service Position - Agilent

    Picture 3: Moving the wash port into the service postion.

    Safety Warnings: Avoid removing capillaries under high pressure, make sure to wear appropriate protective gear.

  4. Disconnect capillary in port 6 of the injection valve. Disconnect the seat capillary from port 5 in the injection valve and connect the needle seat capillary to port 6, so that the flow will go directly from the pump through the needle seat (make sure to work in bypass mode, use Picture 4 as a reference).

    Picture 4: Injection valve ports, standard configuration. Connections:

      1 - From pump

      2 - To metering device

      3 - Plug

      4 - To waste

      5 - From needle seat

      6 - To analytical column

    Keep the vialsampler in the "Needle Up" position.
  5. Close the purge valve and take note of the pressure. Open the purge valve to release the pressure and close the purge valve again for another pressure pulse. Repeat to try and flush out the blockage. Make sure to have Kimwipes or paper towels to collect the mobile phase flow at the needle seat.
  6. Once there is flow backwards through the seat capillary, open the purge valve.
  7. Reinstall the needle seat capillary into port 5, return the capillary that goes to the column to its original position on the injection valve (port 6), flip back the wash port and reinstall the safety cover.
  8. In Lab Advisor under "Injector Steps" click "Needle Into Seat" and then "Reset" to finish the procedure (Picture 5).
    Lab Advisor Injector Steps for Seat Backflush 2 - Agilent
    Picture 5: Lab Advisor Injector Steps - Needle Into Seat + Reset.
  9. End the connection from Lab Advisor, and close Lab Advisor.
  10. Open your CDS software and run the HPLC with normal flow rates. Make sure to work in mainpass mode.


If the pressure is still high after the backflush, you will need a new seat. Contact Agilent Technologies Support for more help.




Learn more on how to effectively operate and troubleshoot your Agilent InfinityLab Vialsampler:

Vialsamplers Agilent InfinityLab LC Series User Manual



Keywords: Liquid Chromatography, HPLC, UHPLC, 1260 Infinity II, needle seat backflush, back flush, LC high pressure, overpressure, high backpressure, high back pressure, injectors

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