check valve and ball valve sequence in a line

dear all,

   In a horizontal gas drain line, what will be the best sequence (upstream/

   downstream relative to each other) of installing a check and a ball valve.The

   drain line came from the Pig Launcher barrel.

   thanks and regards,

   sadanand,
   PE, middle east

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[Non-text portions of this message have been removed] Received on Wed Dec 27 02:21:00 2006