ok to open drain valve with 2000 psi pump pressure?

[ChrisMasterjohn]

Hi everyone,

When I was first trained in HPLC over the summer (by fellow students), I was told not to open the drain valve or loosen any fittings until the pressure had subsided to under 10 bar. However, I don't think any of us fully understand the reason for this (including whether it relates to the column, the pump, the lines, or any combo thereof), enough to be sure of the answer to the following question.

If the column is not connected, and if in fact the pumps are not even connected to the autosampler, is it still advisable to not open the drain valve unless the pressure in the pump has subsided to atmospheric levels?

The reason I ask is that I am currently doing a pressure decay test. I have now fixed the A pump to the point that it is holding pressure nomally, but there is still a leak in the pressure of the B pump. So, say I do this test and the pressure in A is 4000 psi but the pressure in B falls almost immediately, then I remove a check valve to sonicate or replace it. I must prime the pump again, which requires opening the drain valve, but the pressure in A remains high. Can I open the drain valve?

If not, is there a convenient and safe way to remove pressure from pump A?

Thanks,
Chris

[danko]

I assume you're talking about the purge valve/s. Anyway, you can open whichever valve you wish (dispite of the pressure). Nothing harmful will happen.

Best Regards

P.S. A good routine is to ask "why" when the trainer tells funny stories.

[Bruce Hamilton]

My reasons for not quickly dropping pressure are:-

1. Mobile phase dissolved gases undissolve, and usually form bubbles in locations I don't want them.
2. Disruption of dynamic seals, which may then leak ( mainly applies to older systems ).
3. It may not be part of the HPLC design specification ( applies to those who respect engineering aspects of pressure systems ).

If those issues don't concern you, feel free to quickly drop pressure. I find it's easy enough to put a length of narrow bore peek on lines to slow rate of pressure drop.

[danko]

1. Mobile phase dissolved gases undissolve, and usually form bubbles in locations I don't want them.

It only applies if 2 or more liquids of a different nature are mixed under the high pressure, prior to the pressure release – which obviously is not the case here. Otherwise it’s just going back to the pressure that was in the eluent reservoir i.e. atmospheric. It doesn’t get any worse or better to apply pressure and than release it, if no gasses are introduced underway.

3. It may not be part of the HPLC design specification ( applies to those who respect engineering aspects of pressure systems ).

Sounds like a speech delivered by a well-trained politician

Best Regards

[Csaba]

Mobile phase dissolved gases undissolve, and usually form bubbles in locations I don't want them.

Rapid pressure drop is my favorite way to get rid of a persistent bubble in the pump head. (I have heard that some columns don't like rapid pressure drop, true or not, I don't know.)