Teflon tape is more of a lubricant the seal should be made by the taperd threads conforming to each other.
I disagree. All NPT threads are designed to be used with a sealant. For metal to metal seal NPTF (dryseal or AKA National pipe thread-fuel) thread form should be specified. From the machinery’s handbook:
American National Standard Dryseal Pipe Threads for pressure tight joints—
Dryseal pipe threads are based on the U.S.A. (American) pipe thread; however, they differ in that they are designed to seal pressure-tight joints without the necessity of using sealing compounds. To accomplish this, some modification of thread form and greater accuracy in manufacture is required. The roots of both the external and internal threads are truncated slightly more than the crests, i.e., roots have wider flats than crests so that metal to metal contact occurs at the roots and crests coincident with, or prior to, flank contact. Thus, as the threads are assembled by wrenching, the roots of the threads crush the sharper crests of the mating threads. This sealing action at both the major and minor diameters tends to prevent spiral leakage and makes the joints pressure tight without the necessity of using sealing compounds.
Joe,
Grinding off the first few threads may prevent bottoming out and I have the best luck with fuel fittings using Permatex Aviation form a gasket # 3.
