Using an AUX EPC for helium pressure control at the inlet of a Markes Thermal Desorption unit

Hello everybody,

Our GC-MS has two setups:

- classic: GC injector - column - MSD,

- less classic: thermal desorption (TD) unit - transfer line until GC oven - ultimate union - column - MSD.

The less classic setup operates at constant helium pressure controlled though a manual valve and a gauge installed before the TD unit and after the gas filters. There is the need to swap columns between setups as they are different.

We have an unused AUX EPC installed (I think it was meant for a purged union for backflushing purpose) and I was wondering if I could connect one of the outlets of that EPC to the inlet of the TD unit to start controlling the pressure though the GC-MS software. This way I would have a better control of the method pressure and, most importantly, I could leave both columns in the oven no matter what setup I'm using (I would always control a small pressure of He in the unused column).

However, I have been told that it could not be that kind of EPC. It had to be a Split/Splitless or Multimode EPC.

Can someone explain what is the difference between those EPC's?

Thank you.

Cheers.

Parents
  • For details, see the 7890B Advanced Operation manual pages 27-31.  A few things to know.  You need 20 psi higher pressure in front of any pressure regulator. For example, if you need to control 50 psi downstream you need 70 psi or more before the controller (up to the 100psi max for EPC modules).  When an Aux EPC channel is used to control pressure for backflush, a bleed restrictor attached to a tee is used in the supply line to the Purged Ultimate Union. That bleed flow is necessary for decent pressure control. If there is nowhere for the excess pressure to go the pressure can build to match the supply. 

Reply
  • For details, see the 7890B Advanced Operation manual pages 27-31.  A few things to know.  You need 20 psi higher pressure in front of any pressure regulator. For example, if you need to control 50 psi downstream you need 70 psi or more before the controller (up to the 100psi max for EPC modules).  When an Aux EPC channel is used to control pressure for backflush, a bleed restrictor attached to a tee is used in the supply line to the Purged Ultimate Union. That bleed flow is necessary for decent pressure control. If there is nowhere for the excess pressure to go the pressure can build to match the supply. 

Children
No Data
Was this helpful?