Chromatography Forum

Hi, im a first time poster but have found plenty of great info on here. In our lab we are having a problem with an agilent 6890 GC fitted with two 6 port valves. One of the actuator sometimes fails to switch the valve to the 'ON' positon, but never to the OFF position. this is what we've tried so far:
checked the solenoid valves by switching them over
switched the valve drivers- to check its not an electrical problem
swapped the actuators around.

from this we concluded its definately the one actuator that is the problem. then we replaced all the 'o' rings in the actuator, thinking maybe that air is passing through rather than pushing the piston. And still its not functioning properly. So, is this a dead end trying to fix this, and should we just get a new actuator??

any thoughts on this would be appreciated. cheers Nick

It would appear that you have tried most things that I can think of. I have some questions.

1. Check the bearing that the drive shaft goes through. The drive shaft is the part with the screw driver slot in it.

2. You should also check that air is not leaking out of the connector on the actuator. There was a batch of plastic tubing that was slightly under size and this caused some instances of leaks.

3. Does the valve try to rotate.

4. Check that you do not have the situation where you switch the valve on and forget to switch it off at the end of the run. This would give the impression that the valve is not switching on for the next run.

5. How do you have the valves configured and are you running with a ChemStation.


Gasman

Hi Gasman,
thanks for the reply.
1. we inspected both actuators when we switched them over. it all looked Ok to me. But maybe I'm not sure what to look for in the bearing if it might be damaged.

2. checked the tubing connectors with snoop and couldn't find a leak.

3. the valve is definately trying to rotate. you can hear air hissing from the outlet/exhaust of the solenoids, which is why I initially thought the solenoid was broken.

4. We use chemstation, and the timings of the switch are programmed in the runtime events, as well as turning them off at the end of the run.

5. the valves are both switching valves. one is used for backflushing a pre-cloumn to vent, the other directs the flow from the main column to different detectors (FID, ECD).
Cheers,
nick

Have you tried to turn both valves manually? If the one that is not switching consistently is more difficult to rotate the issue may be with the valve and not the actuator.

If you can hear air CONTINUALLY hissing from the solenoid, then I would say that the solenoid is defective. You should only hear air when you switch.

Gasman

Gasman, i can only hear air hissing from the solenoid when the valve fails to switch, until I dis-engage the valve in chemstation. we did swap the solenoids over (solenoid 1 --> driving V2 and vice versa) yet the same valve remianed faulty. could it still be an issue somewhere with the solenoid??
Ron, both valves rotate quite easily, when the actuators were swapped round the faulty 'valve' worked fine, and the other one started to fail.