Chromatography Forum

Hello,
I got pump leakage during a gradient A:25mM NH4OAc B:MeOH
time B%
0 5
15 65
20 95
25 95
25.01 5
30 5

I got a negative peak around 12min and found a leak at B pump.
Changed the pump seal, first couple runs look good and problem came back after that.
Please help on this issue.

Are you multiplexing? When our selector valve rotors start aging we get a negative spike in pressure when they change from stream to stream.

Also if the piston was not clean or if it was scratched, you could destroy the new seal quickly.

The leakage came from pump B (MeOH) and hard to believe since our LC was just bought this March. Initially the pump seals are made of Graphite and later the engineer change into a teflon one.
I noticed that the leakage happens when B reaches 45%.

Did you change the seals yourself or did you have the service rep do it?

If you changed them yourself, the probability is that you did something wrong (don't feel bad; in my career, experience gained has been directly proportional to equipment ruined ). Change the seal again, and check to make sure the piston is clean and not scratched, that there are no dust particles or buffer crystals trapped between the seal and the piston, that the seal is properly inserted in its cavity, and that the pump head bolts are tightened symmetrically.

If the service rep did the job, call him back in; the seal should not fail that quickly.

The rep changed the seal and failed so fast. actually this happened after I trying to reverse flush the column by B(MeOH) at 0.1ml/min overnight.
Did the MeOH swell or shrink the Teflon seal a lot?
Thanks.

Mostly , teflon seals ( yellow , white or colorless seals )are used for normal phase solvents ; such as hexane , iso-octane , ethyl acetate etc.
They are not very suitable for methanol and acetonitrile and leaking easily with those solvents.

Use gray or black seals for reverse phase.( High molecular weight polyethylene seals and graphite filled )

Did you check the piston? The piston was causing me trouble with leaks with this pump.

We just bought this LC-20AD this April and did not use much. Not sure it is piston/plunger causing the leaks.

Did you check the piston? The piston was causing me trouble with leaks with this pump.

We just bought this LC-20AD this April and did not use much. Not sure it is piston/plunger causing the leaks.

Did you check the piston? The piston was causing me trouble with leaks with this pump.

Nonetheless you should look at it. We also bought our LC-30AD in April and there was a leak in the pump. I did not look at the timepoint of leakage but the rep changed the seals three times and the leakage did not disappear. I had a look at the pistons using a microscop and there were scratches. Finally the whole pump was changed. Now it works well.

We just bought this LC-20AD this April and did not use much. Not sure it is piston/plunger causing the leaks.

Finally the whole pump was changed. Now it works well.

Even after the rep changed the seals and only worked for just 2 days and new problems are coming!
no leak now but the pressure goes up and down every 2 min after 10 min and please see pic. The red one is pressure and pink one is the blank trace at 254nm. Please help on the problem!

We just bought this LC-20AD this April and did not use much. Not sure it is piston/plunger causing the leaks.

Did you check the piston? The piston was causing me trouble with leaks with this pump.

Nonetheless you should look at it. We also bought our LC-30AD in April and there was a leak in the pump. I did not look at the timepoint of leakage but the rep changed the seals three times and the leakage did not disappear. I had a look at the pistons using a microscop and there were scratches. Finally the whole pump was changed. Now it works well.

That looks like flow fluctuations. Might be intermittent sticking check valves, but more likely air bubbles. Make sure your degasser is functioning and that you don't have any loose connections on the intake side of the pump which might allow air to be aspirated.

Hi

First off I am guessing you have the 20-AB pump rather than the 20-AD pump, ones a binary and ones a quat.

Shimadzu pistons and likewise their seals are very small and so have to work alot harder for a set flow, e.g. 1ml/min when compared to the Agilents and Waters of the world. This also means they wear quicker and leak faster ( although 2 days is a bit extreme ).

As Tom said your problem is a leaking check valve, try replacing or sonicating them.

When you have cleaned the checkvalve or changed, add 5% water to the B chanel (methanol), so the problem dosent come back.

BR