In the vast world of fittings, threaded fittings play a major role. They are ideal for fast assembly and disassembly and give you an opportunity to solve any possible faults, maintenances and malfunction. In particular, two types of threads are mostly used, especially in hydraulics: BSP thread and NPT thread.
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NPT thread accounts for National Pipe Thread and represents the American standard complying with the norm ANSI B1.20.1. After the BSP thread, it is probably the most used one in the field of hydraulic fittings. It features a 60°- thread angle and it is characterized by a conical thread and not cylindrical one. They usually ensure a higher water tightness, even though the use of a gaskets is still recommended. You can refer it to as MPT, MNPT or NPT (M) for male external threads and FPT, FNPT or NPT (F) for internal female threads. Both threads have the same spacing, angle (60 degrees) and form (flat peaks and depressions).
The BSP thread form stands for the British Standard Pipe and is common in Australia and in the Commonwealth countries. The BSP threads were adopted at an international level for the interconnection and sealing of pipes and fittings. The BSP standard incorporates the threads following standard Whitworth, which was developed in as the first thread standard in the world and it is now extremely popular at an international level for the connections of pipes and fittings.
There are two types of BSP threads:
– BSPP (British Standard Pipe Parallel). Reference standard: ISO 228. This thread is used in Europe and has a cylindrical thread resulting from the “Whitworth” thread, but with different sizes and spacing. It is known as GAS cylindrical thread. The mechanical seal is reached with a 60° concave flaring on the male fitting. The seal with an O – ring gasket is located on the female fitting cone. The seal with flat seat on the male and female parts is guaranteed with a copper gasket.
– BSPT (British Standard Pipe Tapered). Reference standard: ISO 7/1. It is used in Europe and has a conic GAS thread. The seal is reached with the deformation of threads between the male and female part. BSPT is similar to NPT, but there is an important difference. The thread angle is 55 degrees instead of 60 degrees, which is usual for NPT. Therefore, an NPT fitting will be inserted in a BSPT connection or vice versa, but they will not be sealed. The BSPT fittings are a common connection method in China and Japan, but they are very rarely used in North America, unless the equipment to which they are connected has been imported.
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The main difference between BSP and NPT threads is mainly connected to “where” than to “what”. While NPT is prevalent in the USA and Canada, BSP is the main standard in the United Kingdom, Europe, Asia, Australia, New Zealand, South Africa and many other countries. Furthermore, to sum up, the NPT and BSP threads are not interchangeable due to the differences in the thread forms. The NPT threads are sharp in peaks and valleys, where BSP threads are rounded. In particular, the NPT thread angle is 60 degrees compared to the BSP 55-degree angle.
Right for this last difference, it is good to choose the suitable thread in order not to cause any fluid leakages or faults under pressure.
Pressure systems in the process industry use different ways of sealing depending on the geographical region, size of the pressure system, and environmental circumstances. Regional differences and industry preferences are also determining factors in the type of seals used. For example, many pressure systems on ships use BSPP adapters, while applications in the oil and gas industry tend to use NPT fittings. Following is a brief overview of each type of fitting, along with an explanation of the regions and applications where they’re best suited.
NPT (National Pipe Thread) seals are the most popular type of seal used in pressure calibration systems in the U.S. and Canada. NPT male adapters have a taper thread that wedges into the female NPT adapter. They seal due to the "out of roundness principle," which means that the male stretches the female fitting until there is so much force that the connection can hold pressure. One of the challenges with this design is that when you connect stainless steel to stainless steel, over-tightening or poor lubrication can cause galling and damage to the threads. Thread sealant is needed to seal, but only 2 turns of thread sealant is required. Any more than that and the seal can leak around the thread sealant. Ralston Instruments offers a wide variety of male NPT adapters , male Quick-disconnect NPT adapters, male NPT calibrator adapters, female NPT adapters, female NPT gauge adapters and female Quick-disconnect NPT gauge adapters.
BSPT (British Standard Pipe Taper) is similar to NPT but there are a few important differences. The angle across the flanks of threads (if you sliced the fitting in half long-ways and measured the angle from root to crest to root) is 55 degrees instead of 60 degrees as it is for NPT. Another important difference is that for many BSPT pipe sizes, the thread pitch differs from NPT. Thus an NPT male will sometimes fit into a BSPT fitting or vice versa but they will not seal. This is a popular fitting in China and Japan but is very rarely used in North America unless the equipment to which it is attached was imported. Thread sealant is needed to seal the male and female fitting together. We offer adapters to both male BSPT adapters and female BSPT adapters.
BSPP (British Standard Parallel Pipe) is most popular in the UK, Europe, Asia, Australia, New Zealand and South Africa. It is a parallel thread fitting that uses a bonded ring seal to do the sealing. This seal is sandwiched between a shoulder on the male fitting and the face of the female fitting, and is squeezed in place. BSPP pressure gauges have a longer male thread and use a copper crush washer that is squeezed in between the bottom of the male fitting and the bottom of the female BSPP hole, forming a pressure tight seal. No thread sealant is needed to form a seal. Ralston Instruments offers a range of BSPP adapters, including male BSPP adapters , female BSPP adapters, female BSPP gauge adapters, and female BSPP Quick-disconnect gauge adapters.
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