Troubleshooting Low Pressure Issues on LC Systems When No Leak is Detected

Answer

This Information Applies to: Analytical-scale LC systems with a single pump with manual purge valve. It does not apply to systems with Agilent G7167A/B Multisampler or extra switching valves.

Issue

A low pressure through the column is observed, however, no leak is detected or visible in the system. 

Steps to Follow

General system considerations

1. Check the solvent bottles. They must contain enough solvent.
2. Check the solvent intake line. There should be no gas bubbles.
3. Check for clogs in the solvent filter. It should be clog-free.
4. Check the condition of the inlet valve. It should be in good operational conditions and clog-free.
5. Measure the flow rate at the purge valve waste port (purge valve open). It should match the set flow rate.

Sampler 

Visually check the sample flow path for leaks. Salt deposits may be an indicator of small leaks.

1. Look at the needle condition, including the sample loop connection. 
2. Check the needle seat, especially beneath it. 
3. Check the injection valve. The rotor seal should be in good condition. See the article Cleaning or Changing the Rotor Seal of the LC Autosampler Injection Valve.
4. Make sure that all the tubing connections are properly tightened. 

Tips: Touching those areas with a paper towel can be helpful. Using LabAdivsor Maintenance commands to have better access to the needle is recommended.

If one of the previously mentioned parts is leaking, try retightening first. If they are bad condition, replace them.

Pump

Caution: If a seal wash option is installed, turn it off before continuing with the troubleshooting steps.

1. Disconnect the pump outlet capillary on the purge valve on its end at the sampler side. The capillary should be free.

   
   
   Figure 1. Pump head.
   1. Pump outlet capillary, 2. Purge valve, 3. Waste tube
   
   

2. Disconnect waste tubing from the purge valve. Place some paper towels below the purge valve.

   
   
   Figure 2. Pump head.
   1. Pump outlet capillary, 2. Purge valve, 3. Waste tube
   
   

3. Set the pump flow to 5 mL/min with 100% water and turn on the pump.
4. Open the purge valve. There should be continuous dripping from the waste port. Pressure reading from your acquisition software should be typically between 2 and 10 bar due to the high flow rate.
   No solvent should come out of the free capillary. If there is, the purge valve is defective and must be replaced.
5. Close the purge valve. A strong jet of solvent should come out of the free-end outlet capillary. Pressure should be higher than the previous step (around 20 bar).
   No solvent should come out from the waste port. If some solvent is dripping out, the purge valve is defective and must be replaced.
6. Solvent coming out of the body of the pump head is an indicator of piston seal damage. Replace them if necessary. 

If the previous procedures did not solve the issue, or you were not able to perform them, contact your local Agilent Service Representative for assistance.

Learn how to effectively maintain your Agilent LC system: HPLC-1260-1273e - Agilent 1260 Infinity LC with OpenLab CDS High Pressure Errors HPLC-1260-1271e - HPLC High Pressure Errors e-learning courses available fromon courses through Agilent education