Leaky Pump Heads

Are leaky pump heads commmon on the Acquity? I have noticed that my system always has small leaks on the 2 middle pump heads. There are looped wires underneath the pump heads that appear to have been put in there to divert leaks away from the pupm heads. Is this normal? It is most noticeable when doing a seal wash flush, but is constant during normal operating conditions.

Answers

  • Leaky pump heads are uncommon and would result in erratic pump behavior, noticeable chromatographically, additionally, the Console s/w would throw an alert. Seal leaks are uncommon as the high pressure seals have proven to be one of the most rugged parts of the system.

    However, leaks localized to the pump can be caused by other issues, as here. It is more likely that it is the seal wash system that is leaking, not the pump. The seal wash - rinses the back of the plungers to eliminate any salt precipitation. This eventually could cause wear and tear on the seals, but will not cause an issue chromatographically unless the plungers actually failed.

    The leak is either at the plunger seals or the seal wash tubes are leaking. One other issue to check , is whether there is a clog in one of the seal wash tubes. In the latter case, it probably is between the third and fourth head but could be later.

    You can resolve the issue by replacing the seal wash tubes and/or the seal wash seals after you have inspected the seal wash system.

  • "Seal leaks are uncommon as the high pressure seals have proven to be one of the most rugged parts of the system."

    I have had a lot of trouble in the past with pump seals. I generally run a 20% EtOH seal wash solution. I found that the 5 minute seal wash time (which is the Waters Empower default when setting up a new instrument method) did not wash the seals often enough. I was having to change the seals every 2-4 weeks. Since changing the wash time to 1 minute, I have found the seals to be robust.

  • Greetings,

    When considering seal life, several factors should be taken into account. The mobile phase composition is probably the single most important factor. The use of nonvolatile buffers such as phosphates can, certainly, reduce seal life if those buffers are allowed to precipitate in the pump heads. Increasing the organic solvent content in the seal wash will not help in the case of nonvolatile buffers and may promote precipitation. We have conducted studies that indicate that there is a small exchange between the mobile phase and the seal wash solvent. This exchange occurs along the surface of the plunger as it slides through the seal. This exchange is, typically, in the range of tens of nanoliters per hour. However, even this small amount could be enough contact to cause problems if there is a significant incompatibility between the seal wash and the mobile phase. Flow rate is also a factor. A flow rate of 1 mL/min calls for twice as many strokes as 0.5 mL/min in any given unit time. Flow rate effectively compresses or expands time as far as the pump seals are concerned. Finally, the pressure at which the system operates can impact the perception of seal life. It is almost self evident that as system routinely operating at 12,000 psi may experience seal issues sooner than a system that usually needs to hold pressures of 7,000 to 9,000. Since the Community Member (Iconner1) does not include much information concerning their overall usage practices and applications, I can only guess at why they are experiencing shorter seal life. I know that in the six years I have worked with ACQUITY I have had only one instance of pump seal failure,

    Liz

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