標題: NPT和NPTF 檢驗方法 [打印本頁] 作者: rybmsi 時間: 2008-11-27 10:51 標題: NPT和NPTF 檢驗方法 NPT Vs. NPTF Taper Pipe Threads
The two most common taper pipe threads used in the United States are NPT and NPTF. Applications range from electrical conduits and hand railings to high-pressure pipe lines that carry gas or caustic fluids. NPT threads are for mechanical or low-pressure air or fluid applications and require the use of sealing compounds like Teflon tape, to provide the seal. When the application is more critical, and the sealing compound may fail due to high heat or pressure, NPTF Dryseal threads are used. This mechanical seal is produced by the mating and slight crushing of the threads when a wrench is applied to tighten the fittings.
NPT和NPTF螺紋是兩種美國最常用的錐管螺紋。應用范圍從電線管道和扶手到運送煤氣或腐蝕性液體的高壓管線。NPT用于機械的或者低壓的氣體和液體，要求使用密封劑來保證密封。當密封要求嚴格時，密封劑可能由于高溫高壓會失效，這時可以采用NPTF干密封螺紋。當用扳手上緊配件時，這種機械密封會在螺紋配合和輕微的變形來生成密封效果。
Visually, both threads appear to be identical. Both have a ?” taper over one foot of length. Both have the same pitch diameter at the top of the hole of internal threads or end of the pipe on external threads, and both have the same thread lengths or depths. However, there is a subtle difference in the thread form that differentiates the two. The major and minor diameters of both threads differ slightly. With NPT threads, after a wrench is applied, slight spaces at the major and minor diameters may exist that would allow the assembly to leak and therefore a sealing compound is used to fill any gaps. On the other hand, NPTF threads are designed to ensure that sufficient crushing of the entire thread form will take place to produce a mechanical seal.
這兩種螺紋在目測時是相同的。兩種在一英尺的長度上都有3/4的錐度。在內螺紋的孔的頂端或者外螺紋的管的端部擁有相同的中徑，而且擁有相同的螺紋長度和深度。盡管如此，在螺紋牙型上還是有細微的差別。兩螺紋的大直徑和小直徑上有細微的差別。對于NPT螺紋，使用扳手上緊后，在大直徑和小直徑上可能允許裝配后漏氣，因此會使用密封劑來填充所有的間隙。另一方面，NPTF螺紋的設計用于保證在整個牙形上產生足夠的變形以生成這種機械密封。
How does the difference in thread forms effect the tooling used to produce NPT and NPTF threads? Taps are available for both NPT and NPTF threads having the appropriate form to produce each type of thread. Since NPT threaded parts require sealing compounds, it is acceptable to use an NPTF tap for NPT applications. However, NPT taps cannot be used for NPTF applications, as it will likely produce a thread that will leak. The same is true of external threads. In most cases the tap drill is the same for both forms.
牙型的不同如何影響使用的工具來生產NPT和NPTF螺紋？NPT和NPTF螺紋牙形都是采用絲錐來生產每種螺紋。因為NPT螺紋零件要求密封劑，用NPTF絲錐在攻NPT螺紋是可以接受的。但是NPT絲錐不能用于NPTF螺紋，因為它生產的螺紋會漏氣。
The most significant difference in the two threads is the inspection required. Since sealing compounds will be used for NPT threads, only a single plug with a step, known as an L1 plug (internal thread) or a single thin L1 ring (external) are required to check size. However, since the taper and the position of major and minor diameters are so critical to the sealing of NPTF threads, the additional threads in the assembly known as L2 and L3, and the major and minor diameters are inspected with either special plug or ring gages.
最大的不同是這兩種螺紋的檢查要求。因為NPT螺紋要使用密封劑，只要用一個塞規，大家叫L1規（內螺紋）或L1環規（外螺紋）來檢查尺寸。但是，因為錐度和大直徑，小直徑對NPTF螺紋的密封很重要，因此要求其他的螺紋驗規L2和L3規，大直徑和小直徑要用特殊的塞規或環規來檢驗。
