Now before you put the new gas valve on to the pipe you need to check the directional arrow on the gas valve to be sure you are installing it in the right direction.
You need to put pipe compound on the male threads of the pipe and nipples, DO NOT use Teflon tape or any other type of tape or lamp wick on the threads.
You can use Teflon paste, Mega lock or other pipe compounds.
When screwing the new gas valve on to the nipple, make it tight but be careful, the gas valve is made of a soft metal and can crack if you make it too tight.
Once the new gas valve is installed and the nipples are replaced, Note sometimes the new gas valve is not the same size as the old gas valve, so you may need to change the size of the nipples to get the union to line up again.
Very important, do not put any pipe compound on the union seat, and make sure you tighten the union.
Now that the new gas valve is installed, connect the thermocouple.