Middle EFC fail to build up pressure

[xiezz91315]

Hi guys

We have a Varian CP-3800 GC in the lab. The prolbem is the middle pressure couldnot reach the setpoint 60 psi at the 60 mL/min flowrate. Instead, it will stablize at around 40 psi and the system will stay 'not ready'. It's a brand new middle argon type 4 EFC. We just had the varian engineer replaced it a week ago.

I did leak check and found a leak at the middle EFC pencil filter. However, after I fix the leak, the problem still exists. No other leak was detected by using a Restek gas leak detector, model 21-250.

I tried autocalibrate the middle EFC and it made no difference. Although the front type 1 EFC failed to calibrate. But that type 1 EFC has no problem building up pressure.

The argon gas inlet is 80 psi and there is plenty of gas in the tank.

This problem happened before. At that time it was because the backflush solenoid was bad. The varian engieer replaced the backflush solenoid and middle and rear type 4 EFC because they were bad too. It worked for a couple days and failed to build up pressure again. At first the pressure would slowly reach the setpoint if I increased the setpoint 2 psi at a time.
But this trick no longer work now.

This really bothers me. I will really appreciate it if you guys could give me any suggestion on this. Thank you.

[Peter Apps]

Are you setting the pressure or the flow rate ? - if you set the flow to 60 ml/min and the system gets to 60 ml/min at a pressure less than 60 psi it will regulate the pressure at the lower value. It should then show ready - are you sure that it is the EFC that is not ready and not some other part of the system ?

Peter

[AICMM]

xiezz91315,

Can I ask, what are you running 60 mL/min of argon flow for? Are you sure that you are using a EFC that is set up for argon and not helium? I have a local customer who uses a 3800 and I will ask him about his EFC's today to see what insights he may have.

Best regards.

[xiezz91315]

Are you setting the pressure or the flow rate ? - if you set the flow to 60 ml/min and the system gets to 60 ml/min at a pressure less than 60 psi it will regulate the pressure at the lower value. It should then show ready - are you sure that it is the EFC that is not ready and not some other part of the system ?

Peter

Hi Peter

I can set both the pressure and the flow rate. It worked before. The system will reach 60 psi at 60 ml/min.

I'm sure it's the middle type 4 EFC that is not ready. Everything else shows ready except middle flow and column (and that is because of the middle flow, right?).

Thanks
Shirley

[xiezz91315]

xiezz91315,

Can I ask, what are you running 60 mL/min of argon flow for? Are you sure that you are using a EFC that is set up for argon and not helium? I have a local customer who uses a 3800 and I will ask him about his EFC's today to see what insights he may have.

Best regards.

Hello

I'm running 60 ml/min of argon as a carrier gas through liquid and gas sampling valve to the packed column.

I'm not sure whether it's for argon or helium. But the EFC is set by the Varian engineer and he knows what our system. I think it will work for both gas.

Thank you very much for helping me.
Shirley

[Peter Apps]

Hi Shirley

Assuming that the gas flow resistance of the column stays the same, the flow rate will increase with the pressure. There is only one combination of resistance, pressure and flow that will give 60 ml/min at 60 psi. To get both flow and pressure to these selected values you also have to adjust the resistance - which you cannot do because it is determined by the column.

Have you changed the column ?

Peter

[AICMM]

xiezz91315,

I talked to one of my customers who is running 3800's. He said you have to tell the flow controller whether it is working with helium or argon but you had to do this at the instrument. You could not simply do it in the software. He was not sure why but that was his experience. He also stated that the flow controller was not purchased for a particular gas but rather that you had to designate what gas the flow controller was handling. Therefore, you did not buy an argon flow controller but rather a general flow controller that you have to set up for argon gas.

By the way, it would make a big difference whether it was set for helium or argon. My suggestion is to look on the instrument itself to see what gas the flow controller is trying to regulate.

Best regards.

[xiezz91315]

Hi guys, thank you very much for your replies. The problem seems fixed, or is to say at least it's working now.

What I did is raplacing the viton ferrule of the pencil filter for the EFC. I've mentioned before that I found a leak at the pencil ferrule and fixed it by tightening it. The thing is the leak showed up again! I retightened it and lost the leak again. But I kept concerning about it since it's the only reason I can think of that caused the pressure problem. So I decided to replaced the ferrule anyway. And you know what, the pressure started to building up after I did that. You can imagine how happy I am. There is a long story about this GC thing.

Thank you very very much for giving me so many advices. I still don't know what kind of gas controller it is. But it's set by the Varian engineer and we told him we will be using argon. So that may not be a problem.

About the viton ferrule, is it normal that it is not always showing the leak? The pressure and flowrate are set the same.