Agilent HPLC Pump Troubleshooting: Pressure Ripple, Leaks and the Purge Valve — Analytical Instrument Guide

The binary and quaternary pumps of the Agilent 1100, 1200 and 1260 Infinity series are common in Indian QC labs, and we work on them often. They are well built and their parts are easy to find, and most of their problems come down to a short list: air, a sticking valve, a worn seal, or the purge valve.

This guide covers the three things people search for most often: pressure ripple, leaks, and the purge valve.

How the pump works, in one paragraph

Each pump head has two pistons working in series. The first draws solvent in through an inlet valve and pushes it out through an outlet valve; the second keeps the flow going while the first refills. A pressure sensor reports the system pressure, and a purge valve lets you send the flow to waste while priming. Depending on the model, the inlet valve is either active (opened electrically) or passive. Every ripple, leak or pressure fault lives somewhere along that path.

Quick reference

Symptom	Most likely cause	Check first
Pressure ripple on one solvent channel only	Air in that channel, a blocked solvent inlet filter, or its degasser channel	Bottle level, inlet filter, purge that channel
Pressure ripple on every channel	A sticking inlet valve, a dirty outlet valve, or a worn seal	Flush with water and purge, then the valves
Ripple that started after running buffers	Salt in the inlet or outlet valve	Long water flush, then clean or replace the valve
No pressure build-up	Purge valve open, or a large leak	Close the purge valve, look for wet fittings
Pressure with the purge valve open	Blocked purge valve frit	Replace the frit
Wet pump head or white salt deposits	Worn piston seals	Replace the seals; use seal wash with buffers
Leak error and the module stops	Solvent has reached the leak sensor	Find and fix the leak, then dry the leak tray
Retention times shifting with unstable pressure	A seal leak or air	Leak check, purge

Pressure ripple

Every piston pump gives a small, regular pressure ripple. What matters is a ripple that's larger than usual, irregular, or growing week by week. Plot the pump pressure as a signal in your data system and watch it for a few minutes at your normal flow. If the baseline ripples at the same interval as the pressure, the noise is coming from the flow delivery, and the pump is the first place to look.

Find the channel first. On a quaternary pump, run 100% of each channel in turn, A, then B, C and D; on a binary pump, run A alone and then B alone. A binary pump has a separate pump head for each channel, so there a one-channel fault can also sit in that channel's valves or seals.

• Ripple on one channel only: the problem is in that channel's path. Check the solvent level and that the inlet line is fully under the surface, replace a blocked solvent inlet filter, and purge that channel with the purge valve open. A degasser channel that isn't removing air gives the same picture.
• Ripple on every channel: look at what the channels share. Rule out degassing and solvent preparation first, then suspect the pump head: an inlet valve that sticks, an outlet valve with dirt on its seat, or a worn seal.

Sticking valves after buffers. A pump left standing with buffer inside is the classic cause of a sticking inlet valve. A long flush with plenty of water sometimes frees it. If the ripple comes back, the valve needs cleaning or a new check valve cartridge. Always flush buffer out with water before you switch to organic solvent or shut down for the night: salt that crystallises in the pump can block the pump, the injector and the column at once.

Leaks

Small leaks give unstable pressure and shifting retention times long before anyone sees a puddle.

• At the pump head: solvent or white salt deposits under the head point to worn piston seals. On an Agilent 1200 that came to us with unstable pressure and shifting retention times, this was exactly the cause: the pump seals were leaking. A pump seal kit is a planned maintenance part, not only a breakdown part.
• At the fittings: check every capillary connection from the pump head onwards. Stop the flow and let the pressure fall to zero before you touch a leaking fitting, then tighten it gently: overtightening crushes the ferrule and makes a new leak. Replace a fitting that is damaged.
• At the purge valve: solvent around the purge valve knob with the valve closed means its seal or the valve itself needs attention.
• Leak error: Agilent modules carry a leak sensor, and when solvent reaches it the module reports a leak and stops. Find the source first, then dry the leak tray and the sensor area. Clearing the error without finding the leak only brings it back.

If you run buffers every day, a seal wash kit rinses the salt off the pistons behind the seals and makes the seals last longer.

The purge valve

The purge valve opens a path to waste so you can prime the pump and clear air without pushing solvent through the column. Three faults are common:

• Left open. The pump runs but the pressure never builds, because the flow is going to waste. Check that the knob is fully closed before you look for anything else. It is the most common "pump fault" with the simplest fix.
• Blocked frit. The purge valve holds a small frit that catches particles, including fragments from wearing seals. With the purge valve fully open and only the waste line after it, the pressure at your usual purge flow should stay low, a few bar. If it reads clearly higher, check that the valve is fully open and the waste line is not kinked or blocked; if both are fine, the frit is blocked and should be replaced. It is a routine preventive maintenance part.
• Leaking when closed. If flow keeps reaching the waste line with the valve fully closed, or solvent appears at the knob, the valve's seal or seat is worn or dirty.

Pressure too high or too low

• Pressure too high: a blockage after the pump, in the inline filter, the autosampler needle or needle seat, a capillary, or the column frit. Work back from the column towards the pump one connection at a time. Each time, stop the pump and let the pressure fall to zero before you open the connection, route the open end to waste, then restart at a low flow and read the pressure. When it drops, the part you just took out of the path is the blocked one.
• Pressure too low: a leak, air, or the purge valve left open. Check them in that order.

Habits that prevent most pump faults

• Flush buffers out with water at the end of every working day: buffer, then water, then organic, and store the column the way its maker recommends.
• Keep the solvent bottles filled and the inlet filters fully under the surface.
• Replace solvent inlet filters when they discolour, or when a channel starts delivering unsteadily.
• Use seal wash whenever you run buffers.
• Replace the seals and the purge valve frit at planned preventive maintenance, not after a breakdown. The rest of the flow path wears too: on one half-yearly maintenance visit to an Agilent 1260 Infinity II, the needle seat and rotor seal were replaced and the flow cell cleaned in the same visit.

When to call us

Call an engineer when:

• the ripple stays on every channel after flushing and purging
• a valve needs replacing or the pump fails its pressure test
• solvent keeps appearing at the pump head after new seals
• the pump reports motor, drive or electronics errors

Send the model and module (for example, a 1200 series binary pump), a screenshot of the pressure trace, the flow rate and mobile phase, and what you have already tried. If the pump is noisy rather than failing outright, our baseline noise and drift guide helps separate pump faults from detector faults.

We service Agilent 1100, 1200 and 1260 Infinity HPLC systems for laboratories in Thane, Ambernath, Navi Mumbai, Mumbai and Pune. A planned AMC or CMC puts seals, valves and frits on a schedule instead of waiting for a breakdown.

Agilent and the model names are used only to identify instruments. Vision Analytical is an independent service company and is not affiliated with Agilent Technologies.