Chromatography Forum

An HP 1050 LC pump is behaving strangely. When it pumps a 0.2% isopropanol in cyclohexane mix there is a +/- 50+ psi pressure swing. When pumping tetrahydrofuran the swing is +/- 3 psi. Pump has been thoroughly rebuilt (seals, check valve, purged, etc) and seems to operate normally. The IPA/CH mix is run through a de-gasser.

Is there something about the presence of dissolved gases or compressability between the two liquids systems that could explain the pressure instability?

Dear erlex,

The last time I used an HP1050 I was delighted to get 3psi of ripple. Your pump is fine!

Cyclohexane, on the other hand, is extremely compressible. I don't know what factor to use, but try increasing the compressibility compensation on your pump.