Chromatography Forum

Dear all,
in the latest issue of LCGC Europe J.W. Dolan published a nice article on check valves failing with acetonitrile/water mixtures. I was intrigued by this article to ask you, the community, how often do you replace your check valves. Primary, I think about ruby-ball check valves. I do replace teh chekc valve only when one fails, approximately every second year although the mobile phase use is acetonitrile/water exclusively.
Cleaning and sonicating the valves will extend their life for some months but finally tehy must be replaced. I do not even try to dismantle them and clean due to a very high probability that they will be contaminated with dust.

Same here. I only replace this when it fails. I will usually engage the vendor's service engineer to perform the replacement.

I have heard of this phenomenon described in the said article and it seems to be attributed to the formation of some sort of polymers coating the ruby ball that causes the check valves to fail. Agilent LC systems uses ruby ball check valves but I know that certain HPLC vendors do not use ruby ball type check valves, which may not suffer from this phenomenon.

You can also replace the Ruby/Sapphire combo w/ after-market ceramic units if your instrument vendor of choice doesn't offer them.

Hi, there is no issue of replacing the check valve with another one of same or different manufacturer. The issue is about how often the valves are replaced and whether you have the problems and need to replace them often.

I have eight Agilent systems, 1050s and 1100s. We use water-ACN mixtures a lot. I've never had to replace an outlet check valve. We've gone through a few active inlet valves, maybe every few years, when they fail, not a big deal. We do carry a spare of both types.

I only replace check valves when they fail which is very rare. Maybe once every 3 or 4 years. We use both methanol and acetonitrile in our mobile phases and mostly phosphate buffers or no buffer for our UV systems.

In the above mentioned article prof. Dolan focused his attenetion on the inlet check valves. Because the difference in pressure before and after the inlet valve is not sufficiently large there are sticking fenomenon with this valves sometimes. This is not the situation with outlet valves where this difference in pressure is higher.
Until now I didn't know what in fact a concept "active inlet valve" means. Such concept is used by Agilent for their inlet valves. When read the artcle I understand that this means that the motion of the ruby sphere in the valve is assisted additionally possibly by some type of spring.

In my experience of about 20 years of RP-HPLC using mobile phases with CH3CN, water and buffers, inlet check valve failing was a very frequent trouble, but not so serious. Only in one case I had to replace the valve, normally sonication in methanol is enough to restore the good working and requires a minimum loss of time. This problem could appear also in new equipment, specially if they are not used for some days. Now I have four HPLC systems working every day with CH3CN/water mixtures and the frequency of this trouble is very low.

I very rarely have problems with check valves. I run ceramic units exclusively and rebuild my pumps, check valves included, annually whether they need it or not. It might seem to be overkill, but my unscheduled downtime is very close to non-existent and I like it that way.

Alexander Stoyanov:
The "active inlet valve" on the Agilent systems is actually an electronic on/off valvue. It is not a true check valve. I believe they chose this design because of the problems with other inlet valves.

Also, many years ago we had this problem with Beckman pumps. We solved the problem by adding 0.1% phosphoric acid to the mobile phase. I still use this combination whenever possible.

Interesting, the majority of users did not have significant problems oeprating HPLC systems related to check valves both inlet and outlet. I do run twelve LC systems, of which 10 in micro/nano mode, with acetonitrile/water/formic acid as mobile phase only. As posted earlier I did experience check valve failure only after a long time operating (>2 years) but than I had to replace both inlet and outlet valve. Therefore, I was wondering about the frequency of failure occurring for inlet valves described in the article by Dr. Dolan.
The active check valve from Agilent might be a good solution, however, what about the costs replacing those when they fail? The "normal" check valves are already expensive enough. And, does somebody know how long do these active valves live?

Alexander Stoyanov:
Also, many years ago we had this problem with Beckman pumps. We solved the problem by adding 0.1% phosphoric acid to the mobile phase. I still use this combination whenever possible.

What about pH of mobile phase adding H3PO4?

The pH of 0.1% H3PO4 is about 2. I have used this combination for many years on Agilent systems, without problems. Also, since the solution does not contain any dissolved solids/buffers, you can shut down the system without worrying about precipitation. So, if you are using an acidic mobile phase below pH 5, try this combination instead.

Regarding the active inlet valve, there is a replacement cartridge that should be changed every year. It is not very expensive. You do not need to replace the entire unit. And I usually wait more than a year.

As has been reported here in several previous threads, the problem of sticking check valves almost universally applies to using pure acetonitrile on pumps with ruby ball /sapphire seat check valves. If you add 2%, or more, water to the acetonitrile, the problem usually goes away.

This problem was really common in pumps from 1970s to 1990s, and is much less common now, although my Agilent 1100 preparative pumps suffer from it ( probably because of the old valve cartridge design ). It could also be that the preparative system is used much less frequently than the analytical systems. Storing the system in 1:1 Acetontrile/water greatly mitigates the problem.

The Agilent 1100 analytical pumps are certainly much less susceptible to it, but I still pump water through the acetonitrile channel every month or so, just in case there is a deposit building.

Please keep having fun,

Bruce Hamilton

We use 100% acetonitrile in our Shimadzu systems (ruby ball) and rarely have check valve problems with those pumps. Of course, we do refilter the acetonitrile daily (when it gets topped up) so if there is a polymerization problem, perhaps we filter it out.