Please give some more details on GC and valve. Are you sure that you use a 6-port valve with GC?

Did you run a leak test?

The GC is 6890A  series, and I am sure this GC has 6-port injecting valve for gas samples.

actually i used electric leakage detector to find the leak, is there any way for running a leak test?maybe in GC?

Check out this document. It is maybe helpful.

http://www.chem.agilent.com/Library/Support/Documents/a15718.pdf

Thanks Marc, but i have leak at Sample Injection valve of GC not in the inlet!

Change liner. Change spta. Change glass wool.

Hi Samaneh!

I assume you have a VICI/Valco valve in your system?

If it is driven by an air actuator (there are also electrical ones) don´t worry. Valves are operated by applying a certain pressure on one side of the acuator to turn the valve by 90, 60 or 30 degrees (dependig on type). When switching the 6-valve actuator the pressure is released through an electrical  (usually GC controlled 4/2 position) valve,  which makes a sound like you described. 

Does your valve look like this one: http://www.vici.com/vval/vval.php

Regards

Stefan 

Hello Stefan,

Yes, that is exactly the valve that I have in the GC. then do you think that this sound is normal? and i have no air leak in my system?

Regards,

Samaneh

Yes, I think so.

If you want to make sure: There must be two conduits to the large cylindrical valve body which supply the air pressure (usually 3 or 4 bar). Follow them back to the on/off valve which switches the pressure between the two conduits. This valve has  openings for the pressure release. You can feel the pressure impuls coming out of one of them when the valve switches.

Good luck

Stefan