need to purge a furnace gas line?

I need to relocate my propane gas home furnace by approx. 19" and will need to disconnect the gas line and install a longer line. Once this is complete do I need to purge the gas line in order for the furnace to be able to light? This is a newer philco furnace with a honeywell valve. If I need to purge the line how and where is this done?

It may take a couple of tries to light it, but eventually it should get the gas there to light. Does it have a pilot light? Just get a lighter and hold it there until the pilot lights. A match may not last long enough!

The line is under gas pressure, so as soon as a pilot or valve is opened, it will start purging out the air. If this is an igniter type gas control, it will take several tries. This is why the circuit is designed to repeat start tries.