Agilent 1260 Pump Pressure Fluctuation Troubleshooting

An unsteady pressure trace on an Agilent 1260 Infinity (II) pump usually comes down to a few causes. Air in the pump head, a blocked solvent filter, a leaking valve or worn piston seals. This guide gives an order of checks that narrows the cause down with little effort. It is based on the Agilent help for the G7110B, G7111A and G7111B isocratic and quaternary pumps and on articles from the Agilent Community.

Check air and the solvent side first

Start at the bottle head before you open the pump. Agilent describes a simple test for the solvent filter. With a good filter, solvent drips freely from the disconnected tube under hydrostatic pressure. If hardly anything drips, the filter is partly blocked. The documentation lists gradient problems and intermittent pressure fluctuations as the result. Never run the pump without an inlet filter, because small particles can permanently block capillaries and valves.

In the Community, an Agilent staff member attributes a sudden pressure drop of about 10 bar, with large ripple returning at random, to a check valve problem. An air bubble can block the valve. If purging brings the pressure back, air was very likely the cause. Particles in the valve can produce the same symptom. The advice is to purge, keep the solvent bottle clean and pass the mobile phase through a 0.45 µm filter before use.

For its leak tests, Agilent expects a well flushed system. On the secondary leak page, the help lists a check of degasser performance as its own action when degassing efficiency is low.

The Leak Rate Test as a pointer

The Leak Rate Test in Agilent Lab Advisor measures how tight the pump is between the outlet valves and a blank nut. It moves piston 1 and piston 2 separately. A piston fails if its leak rate is above 3 µL/min. This shows which half of the pump holds the problem. After the test, release the pressure slowly by opening the purge valve.

The help interprets the results as follows.

• If piston 2 fails, the candidates are flushing, degassing, the purge valve, the blank nut, the outlet valve, and piston 2 with its seal.
• If piston 1 fails, the candidates are piston 1 with its seal and the inlet valve. A leak at piston 2 also makes piston 1 fail, because liquid can move through the outlet valve into chamber 2.
• If the second leak rate is higher than the first, liquid is flowing back through the outlet valve. The outlet valve is then leaking.

Symptom, cause and action

Valves

For the passive inlet valve, the active inlet valve and the outlet valve, the manual gives the same trigger, which is internal leakage with backflow. Run the Leak Rate Test after every exchange. An Agilent Community article on the active inlet valve names a bubble or liquid moving back and forth at the inlet as a sign, and also pressure fluctuation above 2 bar. It distinguishes cartridges for 400 bar and 600 bar, depending on the pressure rating of the pump. When installing, tighten the nut by hand first and then turn it no more than a quarter turn with the wrench.

Piston seals and pistons

Leaks at the lower pump head, drifting retention times and unstable ripple point to worn seals according to the manual. When you change seals, inspect the sapphire pistons, because scratched pistons shorten the life of new seals. After a seal change Agilent describes a wear in procedure. Flush with isopropanol at 2 mL/min for 5 minutes. Then, with the purge valve closed, hold 380 bar (pumps rated to 400 bar) or 580 bar (pumps rated to 600 bar) for 15 minutes. Do not switch directly between buffers and isopropanol. At the end, replace the purge valve frit.

When reinstalling the pump head, tighten evenly. The Community describes two to three turns per bolt, alternating sides, then another quarter turn each. Never fully tighten one bolt while the other is loose.

Purge valve and frit

Replace the frit after a piston seal change or when it is contaminated. Agilent warns against turning the purge valve while it is mounted, because the rubber O ring can break. Do not lift the pump by the purge valve, or it may start to leak.

Multi channel gradient valve

On quaternary pumps a cross port leak in the gradient valve can mix solvent from unused channels into the mobile phase. It shows up as pressure fluctuation and retention time shifts. In the bubble test you draw one air bubble into each solvent line and mark it. Pump channel A at 1 mL/min and watch the other three lines. No bubble may move past its mark. Repeat for B, C and D. For the repair, Agilent refers you to service.

What counts as normal

An Agilent staff member gave 2 percent as the ripple tolerance in the Community. A user with a new 1260 isocratic pump saw 0.5 to 0.6 percent at 2.0 mL/min, and the answer was that this is within tolerance. Column type and restriction capillary also influence the measured value.

Matching parts from the catalog

Check fit against the nameplate and part number before ordering. The Agilent help names the following numbers for the G7110B, G7111A and G7111B pumps.

• Passive inlet valve G1312-60066 for internal leakage.
• Outlet valve G1312-60067 if the second leak rate is higher.
• Active inlet valve body G1312-60025 and 600 bar cartridge G1312-60020. For 400 bar pumps, the catalog lists cartridge 5062-8562 explicitly for the G7111A.
• Purge valve G7111-60061 for G7110B, G7111A and G7111B.
• PTFE frit 01018-22707, which Agilent names for the purge valve.
• Pump head seals. Agilent lists 5063-6589 as the PTFE seal and 0905-1420 as the PE seal.
• Sapphire piston 5063-6586, 100 µL, to inspect for scratches during a seal change.
• Blank nut 5067-6127 for the Leak Rate Test.
• Degasser G4225A, a vacuum degasser module of the 1260 Infinity line, if degassing is the cause.

FAQ

What pressure ripple is normal on a 1260 pump?

An Agilent staff member names 2 percent as the tolerance. Values of 0.5 to 0.6 percent at 2.0 mL/min were considered fine in one Community case. The trend of your own values over time matters most.

How do I tell whether a piston seal or a valve is at fault?

The Leak Rate Test separates piston 1 from piston 2. If a piston fails above 3 µL/min, the cause tables in the help narrow down the parts. A second leak rate higher than the first points to the outlet valve.

Is purging enough when the pressure suddenly drops?

If the pressure returns after purging, an Agilent staff member says air was very likely the cause. If the effect comes back, check the check valves and the degassing next. Follow the manual for your pump for every intervention.

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