I am adding a gas line from my stup up to the range. Presently there is an existing valve a short nipple and a tee with the stup up coming out of the top of the tee. I intend to replace the tee with a cross fitting and add a short nipple and a valve to the stub up to the range then reduce the additional opening in the cross to 1/2inch, add a vlave and proceed to the garage for a new heater. I can not do this and pressure test it unless I test up to and including the existing valve that has live gas on the upstream side. Is this KO to do or will I be leaking past the valve into the live gas?

This response hs nothing to do with my queston.

eh,did I miss something

This is ta natural gas line in a house!

This is ta natural gas line in a house!

Looks like someone's got some gas line to replace.