Leaking from needle seat

Hi, I am currently using a 1260 ALS autosampler (6 port valve) on my HPLC system. However, every time I inject sample, or simply run my method at "mainpass" mode for the injection port, I can see a significant pressure drop and also leaking from the needle seat. I just changed a new needle seat, needle, rotor seal and isolation seal. But it is still leaking.

 

Has anyone seen similar problem before? And also, is there a pressure limit for the injection port? My back pressure is around 100 bar. Is that possible that the back pressure is too high that the injection port can not hold this pressure?

 

Thank you!

  • Hello! I have seen this issue before, and it is usually because the needle is not seated low enough in the assembly, and therefore the connection between needle and seat is not sealing properly. I would suggest going through the steps of replacing the needle in Lab Advisor, and loosen the screw that holds the needle in place, and push down on the upper end that looks like a union while re-tightening the screw. It does not need to be with a lot of force, you just want to be sure it is just about flush with the assembly. Also ensure the vertical part of the needle is well seated in the groove at the top, which helps with alignment.

     

    Be sure to use Lab Advisor (or the Instant Pilot) to replace the needle and/or seat, as it gives you the option to finely adjust the separation distance between needle and seat. I have heard of people replacing the needle when in the fully down/sealed position, but this is not correct and will lead to a lot of trouble.

     

    Please let me know if this helps,

     

    Chris

  • Hi Chris,

     

    Thanks for your advice! I fixed it based on your instruction.

     

    Do you have an idea how much pressure can this needle hold? I am using the system at around 100 bar back pressure (@5% MeOH). I heard from someone that the needle in the injection port can only tolerate less than 90 bar, is that true? Perhaps I pushed the pressure limit of the needle so that it deformed somehow.

     

    Yanding

  • Hello Yanding,

     

    Glad to hear that worked! The needle to seat connection is very resilient to pressure, and can hold at 600 bar and more. I do not believe that would be the reason why the connection failed, it is most likely that the screw or other part was loose and slipped.

     

    All the best,

     

    Chris

  • Hi sir,

     

    I also having a same problem where there is a leak in a needle.. however, the leak occurs occurs at the top of the needle. i also notes that the needle start to leak after i inject the sample (note: no leaking occurs even i inject blank (mp) sample 3 times).. can u rule out any possibilities that this situation could occurs.

     

    Thanks!

  • Troubleshooting steps when any leak is observed in the sampling area:

    • Block port 6 of the sampler’s injection valve with a blind nut and perform System Pressure Test using Lab Advisor twice. In the first execution, leave the injection valve in the mainpass position, whereas in the second one, have it in the bypass position (Instrument Control à Method Parameters). In both cases, use the highest possible pressure setting allowed by the pump unit.
    • If both test executions pass, the system is leak-tight. Hence, the observed leak should have an external source, such as the needle wash system.
    • If both test executions fail, the leak is most likely not in the sampling area. Possible problem sources are the rotor seal, pump head seals, check valves, the purge valve, or the capillary connection between the pump and the sampler.
    • If the test fails in the mainpass but passes in the bypass, the source of the leak is in the flow path section enclosed by ports 2 and 5 of the injection valve. Possible problem causes are a worn seat pill or needle tip, a worn rotor or metering seal, not tight capillary connections, or a broken loop capillary.
    • If the test fails in the bypass but passes in the mainpass, the two grooves of the rotor seal are interconnected by a channel, causing a cross-port leakage.
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