Floscan Pre-Installation Manual for Diesel Models - Manual (Page 3)

3
3
GENERAL MECHANICAL INFORMATION
Threaded Fittings
There are two basic types of threaded joints. One has tapered threads, which produce a metal to metal seal by wedging the
threaded surfaces together, as the fitting is screwed in and tightened. The other has straight threads with no wedging action. It
uses a static rubber o-ring for sealing. FloScan system components use tapered NPT threads.
Tapered threads have several advantages over straight or running pitch threads. If the fitting develops a leak, tightening the
fitting a fraction of a turn usually stops it. Their sealing ability, however, depends on how carefully the threads are formed. In
the real world threads usually have numerous imperfections and won’t seal regardless of how much they’re tightened, unless
a thread sealant is used.
USA Standard Pipe Thread, (NPT)
(National Pipe Thread) threads are tapered and shaped to engage the mating threads on their flanks. This leaves a spiral
groove along their tips, which must be closed with thread sealer, (Dope). Modern sealers usually include thread lubricants.
Thread lubricants are needed to prevent thread galling, and friction welding.