Tapered pipe thread hydraulic connectors – BSPT and NPTF

Tapered pipe thread hydraulic connectors – BSPT and NPTF

Tapered pipe thread hydraulic connectors have an outside diameter that is cut on a cone.

This results in sides that are not parallel.

Two common types of tapered thread connectors are BSPT and NPTF.

BSPT British Standard Pipe Taper

Country of origin: Britain
Thread angle: 55 degrees (Whitworth)
Seat angle: 30 degrees

BSPT is a tapered thread. This means that the outside diameter of the thread is cut on a cone.

BSPT Thread - Not Parallel

The sides are not parallel.

The taper angle is a rise of 3/4″ for every 12″ in length.

This is approximately 1 degree, 47 minutes.

BSPT Thread - Angles

Male BSPT threads mate with female BSPT threads in adaptors.

BSPT female threads are also used in port applications.

BSPT Thread - Male-Female

As BSPT ports seal directly on the thread, the only machining required is drilling the hole and tapping the thread.

BSPT threads can also be used as a machined seat connector.

BSPT Thread - Nut

The thread used in the female swivel is parallel, BSPP.

This is so that the connector bottoms out onto the sealing face.

The female swivel is made as a two part assembly.

The majority of these connections use a crimped nut.

BSPT Thread - Nut

Larger sizes use a wire locked nut.

This increases the pressure capability of the connection.

BSPT Thread - Wire Lock

NPTF National Pipe Taper (Fuel)

Country of origin: USA
Thread angle: 60 degrees (ANSI)
Seat angle: 30 degrees

NPT is the standard American pipe thread.

NPTF is a derivative used in hydraulics. The “F” means that it is modified for fuel use.

NPTF Thread Diagram

NPTF threads have controlled truncation which means that the roots and crests of NPT threads fit more closely with their mating parts than most other threads.

For this reason, NPT threads feel “sharper” than their BSPT counterparts.

NPTF Thread Diagram

NPT threads are also used in port applications.

NPT port threads will look identical to BSPT ports, but it is important that NPT threads are not interchanged with BSP threads.

NPTF Thread Diagram

When NPT threads are used as machined seat fittings, a parallel female thread is used.

This is to ensure that the threads bottom out on the machined seat.

This thread is called NPSM, National Pipe, Straight Mechanical.

All RYCO NPT parts are extemally grooved or notched so that they can be easily identified.

NPTF Thread Nut

A notch results when a groove is machined in a hex.

Larger sizes use a wire locked nut.

NPTF Thread Wire Lock

This increases the pressure capability of the connection.

NPT threads are the preferred thread for very high pressure systems such as jacking systems.

Working Pressure 700 Bar – 10,000

Pipe threads are mechanically very strong because the thread length is generally twice as long as that of an equivalent sized thread such as JIC.

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Hydraulic connector thread forms and their applications

Hydraulic connector thread forms and their applications

If you’re new to the world of hydraulics, it can seem difficult to gain an understanding of the many hydraulic connectors available today.

In this series of articles, you’ll learn about the different types of hydraulic connectors and their key differences, which will assist in making some sense of this complex subject.

Factors affecting development of hydraulic connectors

Two factors have influenced the development of hydraulic connectors:

1: A reluctance to adopt industrial standards between countries
Many of these connector types were developed during the 20th century; a time of fierce industrial competition.

Co-operation between the major industrialised countries was limited for many years due to conflict.

2: The evolution of hydraulic systems
Hydraulic systems have changed a great deal in a short period of time.

Driving this change is the gradual increase of the desired machine output force, which is seen as a pressure increase.

In the previous series of articles introducing the three types of hydraulic connectors we discussed three principle types of connectors:

  1. Tapered threads
  2. Metal seal connectors
  3. Soft seal connectors

Each major industrial region has developed threads and connectors which fall into these categories.

How a thread is defined

There are three main elements that define a thread.

  1. The thread angle
  2. The thread pitch
  3. The thread size, or outside diameter

Other dimensions such as the depth of the thread and the minor diameter are calculated from the above sizes.

The following sections describe some basic fundamentals of threads.

Standards are used in engineering to ensure that parts from two manufacturers will fit together.

Most threads are made to a standard, and have set engineering dimensions.

Angle

The thread angle of a BSPP thread is 55 degrees.

Different threads have different thread angles.

For example NPT is 60 degrees.

Thread Anatomy Angle

Pitch

The pitch of a thread is the length between two crests or two roots.

A ⅜” BSPP thread has a pitch of 19 threads per inch (TPI).

1” divided by 19 is 0.0526”.

Thread Anatomy Pitch

Outside Diameter

The outside diameter of a thread is nominated in the standard.

BSPP is a NOMINAL thread size.

(The diameter is the not the size as stated, but instead, suits the walls of a pipe of that bore size.)

Thread Anatomy Outside Diameter

Depth

The depth of a thread is based on a ratio of the pitch. (d = 0.61 x P).

In this case: 0.61 x 0.526 = 0.032”

Thread Anatomy Depth

Minor Diameter

The minor diameter of a thread is calculated as follows:
md = OD – (2 x depth)
md = 0.64” – (2 x 0.032”)
md = 0.64” – 0.064”
md = 0.576”

Thread Anatomy Minor Diameter

Tapered Pipe Threads

Tapered pipe threads have an outside diameter that is cut on a cone, and the sides are not parallel.

Tapered pipe thread types include BSPT, NPT, UNS, JIS, Metric Taper and NPTF.

Metal Seal Connectors

Metal seal hydraulic connectors use a profiled seat to form a seal.

Common types of metal seal connectors include JIC, DIN, BSPP, BSPP Flat Face, JIS, NSPM, 30 Degree Flare, Komatsu, Metric French GAZ, Metric French Millimetric and SAE (Automotive).

Soft Seal Connectors

Soft seal connectors use an elastomeric soft seal to ensure a leak-free joint, and may use O-rings, encapsulated seals and bonded washers.

Soft seal connector types include BSPP, UNO, DIN, ORFS, RYCOLOK, SAE Pilot O-Ring and SAE Flange.

Summary

The available hydraulic connectors can be defined by two sub groups: country of origin and sealing method.

The table below shows how each region has developed solutions for each of the sealing methods.

Thread Forms Sealing Methods by Country

For a quick introduction to hydraulic connectors check out our series on hydraulic connectors.

Want more information?

Make sure you select the right hydraulic hose for your next project. Download our 15 Keys To Selecting The Right Hose guide today, or read about BSP Thread here.