Chromatography Forum

I saw several similar topics, but I am still confused what to do with my problem. I got a Shimadzu pump which developed an issue with one of the pump heads. I changed both check valves, made sure they work with a plastic syringe, changed piston seal, even changed the pump head block! Only the piston is left unchanged, as far as I can tell. However, the piston looks to be in a very good shape (at 10x magnification). No signs of wear. The pump head does deliver fluid against no resistance: I can see liquid filling up the top check valve when the line going to the mixer is disconnected. But it does not deliver anything when under pressure. The other pump head delivers its fair share. I tested it with the line from the mixer to the dysfunctional pump head plugged. Pressure fluctuates as the plunger goes back and forth but the average flow rate is half of what is dialed on the pump.

Questions: what else other than the piston can it be? Can piston be bad without any visual signs, like scratches? How difficult is to change the piston on this pump?

If there is no leak under the pump head , then it must be a check valve issue.
The inlet and outlet check valves of LC-10ADvp are very similar so they can be easily mixed up.
There must be arrows on check valves indicating flow direction.

You may try check valves from the good pump head in order to locate the problem.

If there is no leak under the pump head , then it must be a check valve issue.
The inlet and outlet check valves of LC-10ADvp are very similar so they can be easily mixed up.
There must be arrows on check valves indicating flow direction.

You may try check valves from the good pump head in order to locate the problem.

There is no leak under the pump head. Is such a leak an indication of a piston problem?

I replaced check valves with new ones from ASI. Inlet and outlet check valves have threads of different diameter, I do not know how you can mix them up. The ASI check valves have inserts showing the direction of the valve. It is also pretty simple to see. Does anyone have issues with ASI check valves right out of the bag? I am checking if they work or not, but it is not very straight forward, and may be I need to check them again.

You were absolutely correct: the problem was in check valves. This is pretty sad because I installed new check valves. I shall talk to ASI, maybe I was doing something wrong. But it is not obvious what I could have done wrong. All I needed to do was to screw the holders in with the inserts in them in correct orientation. Here is the link for the inserts: http://www.hplc-asi.com/inlet-outlet-ca ... lc-10atvp/ Does anybody had a similar problem with ASI check valves?

How about you installed the Pumphead upside down?
The arrow should point up

No, the direction of the pump head was not a problem. I talked to tech support at ASI, and they told me that any check valve can get stuck if installed more than a couple of weeks after purchase. The problem is that they are shipped in IPA. When IPA evaporates, the ball may adhere to the seat. The solution is sonication. They also suggest storing the valves in IPA to prevent them from drying. They have a rather interesting publication listing troubleshooting tips: http://www.hplc-asi.com/content/files/W ... 0Parts.pdf. It has a tip of how to check which valve is misbehaving, the inlet or the outlet one. I think it has to be modified to work with a pump with two pump heads, but the idea is interesting and seem useful for amateur users like myself.

Hi guys, i think probably it may be check valve , try to exchange firstly the inlet check valve with the other working pump head and see if the problem transfered to the good one or not , if not try to do the same with the outlet valves , we had a problem somthing like that with our schimsdzu class 10Avp as your, my problem was that on purge of the pump lines under no pressure valves work well then when i turn valve on to flow mobile phase through column line at first flow runs well then after a while pressure drops gradually and flow decrease till i see no waste coming out and the flow stops but when i loosen the right inlet check valve in my system and reTighten it again i get pressure again , this problem frequently happening with mobile phases have high %B especially acetonitril and more less with methanol , i knew its my check valve , when i sonicate it with methanol water 50% it works good so try to sonicate check valves with water firstly for 20 minutes then with methanol then with isopropanol , i hope i could help you