Understanding how to measure National Pipe Tapered (NPT) fittings is critical for working with pipes, valves, and fittings. Unfortunately, many industries overlook the advantages of proper fittings and how to apply them across various sectors.
NPT fittings are commonly used in various industries and plumbing services. However, their tapered design can make them challenging to work with. This article will guide you on how to measure NPT fittings accurately and select the right size.
What are NPT Fittings?
NPT threads date back to the 1800s. They are frequently used to connect pipes and hoses in various applications, including water treatment, gas lines, and chemical processing.
They are favored for their capacity to create robust seals without requiring extra gaskets. In fact, they are ideal for high-pressure environments. Industries involved in plumbing services can greatly benefit from NPT fittings.
How Do NPT Threads Work?
While conventional threads maintain a consistent diameter length, NPT threads are taperedāmeaning they get more narrow as they extend.Ā
The threads on both the male and female components must match in terms of size and taper angle to guarantee a seal.
A common misconception is that thread diameter is measured at its narrowest or widest point. In reality, it is an average measurement due to the taper.
How to Measure NPT Pipe Fittings
There are several approaches on how to measure NPT fittings, each ensuring you find the right fit for your needs. The steps to follow are:
Step 1: Identify Nominal Pipe Size (NPS)
This measurement refers to the outer diameter of the stainless steel pipe for sizes larger than NPS 14; however, under NPS 14, it does not directly correspond to the outer diameter of the fitting. For example, NPS 12 = OD of 12.75 inches and NPS 14 = OD of 14 inches.
Refer to a reference chart or pipe sizing guide that matches the nominal size and checks against the outside diameter of the fitting thread. These are available through online retailers and your local plumbing supply stores.
Step 2: Measure Outside Diameter
After identifying the NPS, measure the outside diameter of a male fitting or the inside diameter of a female fitting with a caliper or tape measure.
To do this, you’ll need to understand how to measure NPT fittings by starting with the outside diameter at the widest point of the thread and then measuring the inside as well.
Step 3: Measure Thread Pitch
Measure the pitch using a thread gauge or caliper and count how many threads appear in one inch of the fitting. Male and female components should securely screw together precisely, which prevents any abnormal threads or a loose seal.
Step 4: Check Taper Angle
Even though most NPT fittings have a standardized taper of 1.7899 degrees, knowing how to measure NPT fittings accurately includes verifying the angle of the taper. You can confirm the taper angle is correct by using a thread gauge that has a taper setting or comparing the fitting against a known NPT fitting.
This measurement is important as the taper angle forms the seal when the threads are tightened.
Common Misconceptions About Measuring NPT Fittings
- Popular assumption:Ā The outside diameter of a fitting correlates to its size.
- Truth: With NPT fittings, the size is just a reference point and does not always reflect the outside diameter of the fittings.
- Popular assumption:Ā All NPT fittings have the same taper.
- Truth:Ā While most NPT fittings do have a standard 1/16″ taper, there are also variations, such as dryseal and fuel line tapers. Knowing which type of taper you are dealing with when selecting fittings is important to confirm proper fit and functionality.
Additionally, some believe adding moreĀ thread seals or tape on stainless steel productsĀ can compensate for improper thread alignment or pitch. While thread sealant helps create a tighter seal, it wonāt fix mismatched threads or poor measurements.
Tools for Measuring NPT Fittings
- Calipers: To measure the outside and inside diameters of the fittings.
- Thread Gauge: Used to measure the thread pitch and threads per inch.
- Pipe Sizing Charts: These charts will match your fitting measurements to the appropriate nominal pipe size.
Why Accurate Measurement Matters
Achieving a complete leak-proof connection is critical in industries such as plumbing, food processing, or chemical handling. Knowing how to measure NPT fittings accurately prevents issues like thread damage, durability compromise, and increased risk of leaks.
Altering the thread pitch, diameter, or taper angle on aĀ single sanitary fitting can result in downtimeĀ and lost productivity, ultimately leading to system failures and costly repairs.Ā
ContactĀ P&E Flow Technology for guidance on measurement of NPT fittings. Our team of experienced professionals and line of state-of-the-art tools guarantee precision in every fitting, saving you time, money, and potential system failures
