pump head leak

[ChrisMasterjohn]

I'm doing some maintenance on the pumps of Beckman System Gold, with pump model 126. Pump B, which had most recently been running 50% ACN 5 mM NaPO4 during analysis and 100% ACN during column wash, looked very disgusting inside with lots of rust-colored gum.

I scrubbed the inside with isopropynol and chem wipes or a q-tip-like disposable cleaning instrument we have and removed lots of this gum, which also seemed to have a lot of small black particulate matter in it, perhaps the same substance more conglomerated or perhaps wearing pump seal. I cleaned everything as best I could, and I also flushed about 400 mL of water through the pump using the priming valve and a syringe to get rid of any buffer.

Formerly, the pump was failing a pressure decay test without a visible liquid leak. After performing the above maintenance at the end of last week, today I replaced the piston and the high-pressure seal. The new seal was in methanol over the weekend because I had taken it out of the package to briefly soak it on Friday when I found out that our piston was missing a part I had to order, and the tech support person told me I could keep it soaking over the weekend.

Now, however, there is a visible leak on the bottom of the pump head! It is in front of the wash line, where the metal part of the pump head meets the black wash seal housing (I think I'm naming the parts right -- in any case, where the metal part meets the black part).

Ay! What could have gone wrong? I thought I took every precaution as best I could -- what should I do? Try replacing the seal again?

Thanks,
Chris

[ChrisMasterjohn]

I'm not sure what the exact cause was, but I fixed it.

I saw that there was black residue in the line that connects the wash line of the two pumps, so I replaced that piece of tubing. While I was at it, I replaced the solvent lines too. I replaced the high-pressure pump seal and the low-pressure wash seal. Now, the liquid leak is gone.

There is still a pressure leak but I think that is because I'm using a check valve that was marked "old, maybe good" (!) while I was waiting for our order of check valves to come in so I"m going to replace that with a new one.

I'm curious -- can anyone spculate on whether changing the wash seal might actually have solved this problem? The location and behaior of the leak seemed like it was the high-pressure piston seal.

Chris

[tom jupille]

My guess is that you still have a very slight leak from the main seal. Now that you have replaced the backup seal (wash seal) the liquid is staying in between the two seals. If that pump has a washout port (to flush the area between the seals), check to see if liquid is accumulating in there.

[ChrisMasterjohn]

I replaced the high-pressure piston seal and low-pressure piston wash seal simultaneously. I also changed the piston shortly before this. So the seals and piston are brand new.

I put in a brand new outlet check valve today, although I had to replace the tubing that runs from it to the mixer with PEEK becaus the stainless steel fitting was originally fitted into a Beckman check valve and it seems to leak more often than not when connected to an Upchurch check valve, which we are currently using. I initialy had a problem with the fittings not tolerating the high pressure of the pressure decay test, but I tightened them a little better and also lowered the pressure I as using from 4 kpsi to 2.5 kpsi.

I do not see any visible liquid leaks anywhere on the pump, not at the check valves and not under the pump head.

But as soon as the pumps shut off when the pressure limit is reached (on this particular machine I have to shut them off myself through the software or else the pump will keep pumping as soon as it senses the pressure falls, to maintain it at the limit), this pump (pump B) begins losing pressure rapidly.

Any thought of what to address next?

Thanks,
Chris

[DR]

Inlet check valves - replace those cartridges as well (assuming they're also Upchurch)...

[ChrisMasterjohn]

The inlet and outlet check valves (full assembly including body) are brand new, as is the piston and both high-pressure an low-presure seals. So, most of the pump is new, at least all the commonly replced parts.

For a long time, this machine had run with no solvent filtration frits or any inline filters. Also, we had mistakenly been considering precipitation in our column but not our lines or pumps, so for shutdown methods we had commonly switched the B pump straight from part-buffer (e.g. 50% ACN 5 mM NaPO4) to 100% organic (e.g. 100% ACN).

There are currently brand new solvent frits, brand new teflon solvent lines, and a brand new solvent wash line. The teflon lines running from the solvent selector (this is a high-pressure system but each pump can choose between four solvent lines, which is chosen by the software, but involves a little block into which the four potential solvent lines run) to the prime pump valve, and running from the prime pump valve to the inlet chec valve, are old. I did not replace them because I ran out of teflon tubing while replacing the other sections.

So the only parts that are not new are: the pump head itself (i.e. casings, etc), and the aforementioned tubing and associated fittings.

For the pressure test, I block the line that would otherwise go to the autosampler with a union and plug. When the pressure reaches 4000 psi, I shut the pumps off. This system is designed to keep pumping as soon as a slight pressure drop is detected, thus I turn it off manually on the software. When I do this, A retains pressure and B loses it rapidly.

To further isolate the problem, I disconnected pump B from the mixer and plugged the outlet check valve, and ran 100% B. The same thing happens -- rapid loss of pressure as soon as the pump is turned off.

Any suggestions?

Thanks,
Chris