Front Inlet constant leak

I finally got a Helium detector and found out that the leak is from EPC. I didn't detect any leaks from any part of the GC.

Where at the Electronic Pressure Control Module is it leaking?

Thanks for asking Paul.
It's from septum purge outlet, which I guess should be normal as there should be a purge flow. But it's higher than expected. When I put a septum on it to block it, the leak reduces.

Don't block it!  The septum purge flow is set on the GC front panel and in the method. It should be about 3 ml/min.  If you see air in the MS background or tune and blocking this makes that go down, you probably have the total flow to the inlet set too low.  Set the inlet mode to split, 1.2ml/min column flow to the MS and 20:1 split ratio with 3 ml/min septum purge. Let it pump that way for five minutes or so, then look for air.

If the total flow is too low, air diffuses back inside the septum purge and split vent lines - both required exhausts of the carrier gas, and looks like a leak.

Thanks for the advice Paul! I put column flow on 1 ml/min and a purge of 2ml/min in splitless mode, but it works fine. My air and water check is good (water<2%, N<8%). The problem is that I think the tank is running out too fast.

Do a leak down test on the gas supply. You need to have a shutoff valve in the carrier gas supply line immediately before the GC or you'll need to cap off the supply before the GC.

Turn the Inlet, GC oven, and MS transferline to ambient temperature.

Shut off the valve behind the GC

Note the Tank regulator second stage pressure - like 60 psi.

Shutoff the tank...and wait.  The time to wait depends on the amount of tubing and traps between the tank and the instrument and the size of any possible leak. I would suggest you wait at least ten minutes to 1/2 an hour. 

Check the second stage pressure --- did it go down at all?  If it did - you need to find the leak in that system.  If it did not, a helium tank with only 20 to 30 ml/min of gas flowing out should last some months.....

I tested the leaks from tubing using Helium detector and there was none. But I will also try these steps this time to see if there's any leak.

We have an empty and a full tank in the lab. When I was using N2 tanks for my other works I was suspecting that the company does not fill them with liquid. I suspect that it might be true about the Helium tanks. I'm looking for a scale in the department to see the weight difference between the full and empty tank.

Thanks for the helps!

I tested the leaks from tubing using Helium detector and there was none. But I will also try these steps this time to see if there's any leak.

We have an empty and a full tank in the lab. When I was using N2 tanks for my other works I was suspecting that the company does not fill them with liquid. I suspect that it might be true about the Helium tanks. I'm looking for a scale in the department to see the weight difference between the full and empty tank.

Thanks for the helps!