pressure drops without any obivous leaking

[IUpuppy]

Hello everyone again,

we had a leaking problem from the pump assembly from the end of last year and that was when pressure dropping and pressure ripples started to happen. We managed to stop the leaking by replacing the fittings, and now the pressure seems to be stable. However, I noticed that the pressure never goes up to what it normally used to be before the leak(e.g. a particular gradient before the leaking is 1300 psi but now it is only 1100 psi).

At the moment I haven't observed any leaking from the pump assembly. The only cause on top of my head is that maybe the pump seal and the check valves are worn and torn. Does anyone agree with me? Could anyone suggest any other reasons for the pressure dropping? I don't want to blindly service the pump especially when I am not experienced at all, small problem can turn into big problem if you don't know what you are doing...

Another issue from the sample management system is- I noticed that whenever an injection is completed, there will be solvent built up on top of the HPLC vials, the carousel is very wet as a result of that. Is that an indication that the injector needs to be fixed?

I hope my questions are clear enough for people to understand and I do appreciate any suggestions for the problems I have. Thank you all very much for your time!

[Gerhard Kratz]

To earn experiance it means you Need to do things you never ever did before. But it can cause Problems when you do it on an HPLC System you Need to run daily. My recommendation is:
It seems that you Need to maintenance the injector System and your pump head and check valves. Ask the Service organization of the manufacturer to send a technician. Please stand all the time with this technician and look over his shoulder. Ask as much as possible questions. Ask him/her what are the critical Points. Make notes and do it the next time by yourselfe. Or attend a course for Hands on in HPLC. Good luck.

[AaronAIT]

I had a similar problem that had me stumped on an old Waters HPLC until I saw that the pressure dropped only when an injection occurred... turns out there was a leak in the mobile phase line going into the injector, and the leak only made itself apparent when the needle prepared to inject.

In other words - it might not always be the pump that's the problem. The fact that there is mobile phase leaking into the carousel points towards an injector problem.

As Gerhard said above, if you have the money for a technician to come and look at the instrument, follow him/her and draw diagrams, take notes etc. - it'll make paying for the service visit a lot more valuable.

[Peter Apps]

As long as you are getting the required flow, and the separation is working, then a lower pressure is not a problem - it simply means that you have less resistance in the flow line, possibly because your column is in a better state than it was previously.

Peter

[IUpuppy]

Thank you very much Gerhard, AaronAIT, and Peter, you all are very nice! I will see what I can do to get a service technician but I did learn a lot from your replies!

Hyuna

[juddc]

Another issue from the sample management system is- I noticed that whenever an injection is completed, there will be solvent built up on top of the HPLC vials, the carousel is very wet as a result of that. Is that an indication that the injector needs to be fixed?

If I had to guess, I'd say that's where your leak is and where your 200 psi went. Check for leaks in any fittings nearby, replace your injector seals, or simply PM the entire unit and I would guess that you'll be OK. I would also check your pump flow accuracy as well. A meter or so of 0.005" ID tubing should provide sufficient backpressure at 1 mL/min. Some methanol, a 10 ml volumetric flask, a stopwatch, and 10 minutes should tell the tale there.

[cbozova]

Hello everyone again,

we had a leaking problem from the pump assembly from the end of last year and that was when pressure dropping and pressure ripples started to happen. We managed to stop the leaking by replacing the fittings, and now the pressure seems to be stable. However, I noticed that the pressure never goes up to what it normally used to be before the leak(e.g. a particular gradient before the leaking is 1300 psi but now it is only 1100 psi).

At the moment I haven't observed any leaking from the pump assembly. The only cause on top of my head is that maybe the pump seal and the check valves are worn and torn. Does anyone agree with me? Could anyone suggest any other reasons for the pressure dropping? I don't want to blindly service the pump especially when I am not experienced at all, small problem can turn into big problem if you don't know what you are doing...

Another issue from the sample management system is- I noticed that whenever an injection is completed, there will be solvent built up on top of the HPLC vials, the carousel is very wet as a result of that. Is that an indication that the injector needs to be fixed?

I hope my questions are clear enough for people to understand and I do appreciate any suggestions for the problems I have. Thank you all very much for your time!

Hello, i have some experience about Waters HPLC. My opinion is Check Valves or Plunger seals. %90 about plunger Seal but a small chance can be about check valves. Accumator sides seals or check valve generally make problem such this.

[juddc]

Hello, i have some experience about Waters HPLC. My opinion is Check Valves or Plunger seals. %90 about plunger Seal but a small chance can be about check valves. Accumator sides seals or check valve generally make problem such this.

Hey there - Not to be contrary but the OP didn't specify whether or not he was working with a Waters LC. With a 2690/5 a plunger seal or check valve failure in wouldn't cause mobile phase to be leaking into the sample compartment as the OP observed because the sample compartment is above the pump.

[IUpuppy]

Hello again, thanks for all the ideas. Just want to be more specific, I am working on an e2695 Alliance system so it is from Waters. I think both the pump and the injector need to be serviced. Waters provides video to show people how to replace pump seals, plunger seals, check valves etcs on the website. I am not very familar with the injector parts, hopefully the 2695 manual or waters website can help.

Thanks again for all the suggestions!

Hyuna