BSP (British Standard Pipe) and NPT (National Pipe Thread) are two of the most common types of thread standards used for pipe fittings and connections. They have some key differences, and the choice between them depends on various factors, including the location and application of the fittings.
1. Thread Angle and Pitch:
- BSP fittings have a 55-degree thread angle with a rounded crest and roots. The pitch (distance between threads) is expressed in threads per inch (TPI) for imperial sizes or in millimeters for metric sizes.
BSPT thread angle
- NPT fittings have a 60-degree thread angle and are measured in threads per inch.
NPT thread angle
2. Sealing Method:
- One of the most significant differences between BSP and NPT threads is the method of sealing.
- BSP threads rely on the use of a gasket or sealing compound, such as PTFE tape or thread sealant, to create a seal. This means that the threads themselves are not designed to provide a perfect seal.
- NPT threads use a tapering thread form that, when tightened, creates a mechanical interference fit, which helps to provide a seal without the need for additional sealing compounds.
3. Applications:
- BSP fittings are commonly used in Europe, Asia, Australia, and other parts of the world where the metric system is prevalent. They are also used in low-pressure plumbing and hydraulic systems.
- NPT fittings are more commonly used in the United States and Canada. They are widely used in a variety of applications, including plumbing, air compressors, and other industrial equipment.
4. Interchangeability:
- BSP and NPT threads are not compatible with each other. Attempting to mate a BSP fitting with an NPT fitting can lead to leaks and other issues.
5. Sizes:
- BSP fittings come in a range of sizes, both in metric and imperial measurements.
- NPT fittings are primarily found in imperial sizes, although some manufacturers offer metric equivalents.
6. Cost and Availability:
- In some regions, the availability and cost of BSP or NPT fittings may vary. This can be an important consideration when choosing between the two.
In summary, the choice between BSP and NPT fittings depends on factors like the location of the installation, the specific application, and local standards. It’s important to ensure that all fittings used in a system have matching threads to prevent leaks and ensure proper functioning. If in doubt, consult with a knowledgeable supplier or a professional in the field.