NPT (National Pipe Tapered) threads are a standard used in the U.S. for connecting pipes and fittings. They are designed with a taper meaning that as you screw the male thread into the female thread, the diameter decreases and the threads become tighter, creating a seal. NPT threads are widely used in piping for gases and liquids, especially in the plumbing and gas distribution industries, due to their reliable sealing characteristics. Ralston Instruments makes a wide variety of male and female NPT threaded adapters, hose ends and valves.
How NPT works:
1. Tapered Design: Both the male (external) and female (internal) threads are tapered, which means they gradually get smaller as they move away from the open end. The taper allows the threads to compress and wedge into one another as they are tightened.
2. Sealing Mechanism: As the male thread is screwed into the female thread, the taper causes the threads to engage progressively more tightly. This creates a metal-to-metal seal, but due to the gaps in the thread crest and root, a complete seal is often achieved using thread sealant like PTFE (Teflon) tape or pipe dope.
3. Leak Prevention: The combination of mechanical tightening and the use of a thread sealant helps prevent leaks by filling in any imperfections in the threads and providing a more secure, leak-proof connection. NPT threads rely on both this mechanical fit and the sealant to prevent leaks.
4. Hand Tightening and Wrenching: Typically, NPT threads are first hand-tightened, then further tightened with a wrench. Over-tightening can damage the threads, so it’s important to apply the correct amount of force.