Chromatography Forum

Hello,
I would like to ask for help in solving the problem with the stuck VHP valve. There was a problem with reproducibility, from the tube from port 4 leaked very very slowly, one drop every few minutes. I cleaned the rotor and stator, screwed the valve head on - evenly, slowly to the first resistance until the head rested on the valve base. When I started it for the first time, I heard "wrrrr" and an error popped up. I unscrewed the screws 1/2 turn, the valve works, but the leak remains. The stator surface is perfect and the rotor doesn't look bad either. I attach photos.

1. Maybe the valve axis has too much resistance or the motor has lost torque? I would like some suggestions, simple rotor replacement due to its price (ca $ 500 !!) is a last solution, ,?

2. Is it possible to disassemble and remove the entire VHP valve block from the outside after unscrewing 3 screws (red dot)?

https://ibb.co/Kjm9QGS

https://ibb.co/f1Rtp1c

https://ibb.co/7SKj0fF

Regards

To solve the issue, proper service is required. You need to replace the valve rotary seal and any other worn or damaged parts. Usually, the rotary seal is replaced on a regular basis and if no scratches or corrosion are present, the remaining parts may be re-used. *With the Rheodyne style injector valve used in the Agilent injectors, when replacing the outer stator plate, it is very important to carefully re-torque the three socket-head cap screws back down evenly onto the valve body. Damage may result if done improperly (too tight is bad). Have someone with the proper service training perform this task for you. Ideally, take a professional HPLC Service Class yourself https://www.hplctools.com/courses.htm in how to perform the basic HPLC inspections and maintenance tasks which apply to YOUR specific HPLC system(s) to learn the procedures. The skills needed should be acquired by anyone who regularly uses and/or is in charge of each instrument.

Note: A $50K plus (USD) HPLC system requires regular maintenance, inspection and service to operate properly. A/I rotary seals are considered normal maintenance parts. You should have a spare on-site along with other commonly needed consumable maintenance parts (i.e. piston seals, PFTE frits, Bottle filters, Lamp, Needle Seat etc). The cost of maintenance parts is trivial in regard to the value of the instrument, your time and any downtime created by not maintaining the system.

"HPLC Maintenance & Repair Parts To Have on Hand for HPLC Systems"; https://hplctips.blogspot.com/2013/11/m ... d-for.html

"Troubleshooting HPLC Injectors (Manual and Automated)": https://hplctips.blogspot.com/2013/06/t ... anual.html

@ Multidimensional. Thanks for your helpful comments.

However, I would ask for practical comments if there were any problems described above after replacing the rotor seal, even though the entire procedure was performed according to the instructions. In particular, I am referring to the disturbing noise when the valve head is slightly tightened to the position where it begins to touch the valve housing. Has anyone encountered such a problem? It would seem that the degree of difficulty in replacing the rotor seal is similar to replacing the piston seal.

https://ibb.co/ZLKWw24

Regards

It is not clear to me what you have done so far. You stated that a leak at the front face (stator head) of the valve is what started this process. Liquid seen exiting the A/I valve's waste port (#4) is normal when the injector is "injecting". Fluid seeping out of this port at other times usually indicates internal wear or contamination is present and the valve requires service (*Always flush the system with clean buffer-free solution (e.g. IPA or MeOH), column by-passed, to check operation and clean the flow path). A full check of the autoinjector's flow path to check for an obstruction or loose connection would normally occur next. All of the fittings would need to be checked which attach to the valve, the rotor seal, stator ring & head examined and after cleaning and re-assembly, the injector operated in manual step mode to check for flow through the correct paths. In most cases, a leak at the front face of the valve is caused by a loose fitting, but a worn rotor seal or obstruction may also be to blame. We see the most issues with users incorrectly installing the rotary seal*NOTE: The valve itself is not normally removed for service (unless liquid has leaked back into the area behind the rotatory seal and/or bearing which may then require valve replacement). Failure to put the seal in correctly along with the ring and front stator face & head will result in leaks. The design used for this model is poor as many client's have difficulty adjusting the SHCP which secures the stator head.

Rotor Seal / Needle Seat Material: Another problem that relates to this valve is the 600 bar rated PEEK rotary seal used in some versions (vs the 1300 bar seal). The PEEK versions wear out FAST and require regular replacement or internal leaks may damage the inside of the valve. Also, we see a lot of these systems running solvents that are not chemically compatible with PEEK (i.e. THF, Chloroform etc) so should not be used with the PEEK rotor. The same issues apply to the needle seat as it is available in VESPEL and PEEK versions. If using the PEEK parts, make sure you are not using chemicals which are incompatible with it.

Noises which are heard during operation of the injector valve should not include a wurrrring sound. The valve is driven with a stepper motor. Normal operation makes a high pitched steady tone as it rotates to one of two positions. If the motor-to-valve coupler or encoder is damaged (or the valve has been reset), then it is possible it will make a long steady noise lasting a few seconds as it searches for the correct initial calibration position. If it lasts longer or stutters, then mechanical damage is present. Did you perform an A/I reset? Are you sure the noise heard is from the A/I valve? Is it still leaking after properly being serviced? If so, from where exactly?

@ multidimentional Thank you very much for your many useful comments.

It seems to me that in this model, the designers tried to simplify the replacement of the rotor seal by slowly and successively tightening screws until the stator head touches the stator ring (this moment can be felt on the hex wrench) - the stator head and rotor seal are parallel and sufficiently tightened. In previous sampler models, where the stator head did not touch the stator ring, it was inherently much more difficult to achieve the parallel position of the rotor seal / stator head and the tightness. I'm right?

Mobile phase can flow from port 4 only for short time when the metering pump piston returns to the "home" position - VPH valve is in the mainpass position and the needle is still in the injection port - only then port #4 is connected to the mobile phase line.

In my case, the drop is very very slowly leak from the tube from port #4 during the analysis, it does not leak from the valve housing.

Can you just explain to me what does "SVHC" mean?

Best regards

You wrote: "In my case, the drop is very very slowly leak from the tube from port #4 during the analysis, it does not leak from the valve housing". - So liquid is leaking out port #4 during an analysis, not most injections? Yes? That implies you have not properly serviced and/or re-assembled the injector valve correctly.

The rotor seal, stator and/or other parts may still be damaged (no idea what, if any, parts you replaced. I think none). This newer head design uses pins to reduce the chances of the user over-tightening the valve face damaging the parts inside. The previous model used set-screws, adjusted to a specific height acting as "stops" (like the pins do) to reach the pressure max depth. New parts may be needed when over-tightened, then proper re-assembly and pressure testing.

Please consider hiring someone to service the system/valve and if your employer allows, hire someone to provide an on-site maintenance training class, that is specific to your instrument configuration, for hands-on training in the maintenance procedures. Everyone that uses these tools professionally should have this training and not rely on having to call service in every time the system breaks down. You have to understand how these work to use and troubleshoot them. *Please never use a system that leaks to collect data.

Thanks again.

And can you just explain to me what does "SVHC" mean?