Ultimate Guide to Hydraulic Fittings


Detailed Overview of Global Connection Standards

Hydraulic systems rely on robust and precise fittings to manage fluid flow efficiently and safely. Our comprehensive guide explores the specifics of various types of hydraulic fittings, covering American, British, German, Japanese, and ISO standards.

American Hydraulic Fittings

NPT (National Pipe Tapered):

The NPT is a staple in U.S. fluid and gas transfer applications, used extensively for over 100 years. It features tapered threads that ensure effective sealing when engaged, and is available in a range of materials including iron, brass, carbon steel, and stainless steel to meet different pressure requirements. The nominal pipe size is determined by measuring the thread diameter and subtracting 1/4".

NPTF (National Pipe Tapered Fuel):

This fitting is preferred in fluid power systems for creating strong, leak-proof connections without the need for extra sealants. The metal-to-metal seal is formed by the deformation of threads during tightening. The nominal size is established by measuring the thread diameter and reducing it by 1/4-inch.

NPSM (National Pipe Straight Mechanical):

The NPSM design incorporates a straight thread and a 30° seat in the female components, with a matching 30° chamfer in the male components. The seal is achieved through the mechanical compression of the 30° seat against the chamfer, allowing compatibility with NPTF males if chamfered correctly.

SAE Standards:

These standards cover a range of fitting types including ORB, JIC/37°, 45°, ORFS, and 4-Bolt Flange, each designed to meet specific sealing needs and pressures in fluid power systems.

ORB (O-Ring Boss):

ORB fittings use a straight thread and an O-ring seated in the male part to create a tight, leak-proof seal when screwed into a female port, making them ideal for high-pressure applications.

JIC (Joint Industry Council 37° Flare):

JIC fittings are universally popular in hydraulic systems, featuring a 37° flare that ensures a reliable seal by mating the coned surface of the male flare with the flared tube of the female.

ORFS (O-Ring Face Seal):

ORFS fittings provide the best leakage control and are used extensively in high-vibration environments. They have a straight thread and use a flat face with an O-ring on the male part that compresses against the flat surface of the female when tightened.

British and ISO Standard Fittings

British Standard Pipe (BSP):

The BSP standard includes BSPT (tapered) and BSPP (parallel) types. BSPT seals by thread distortion and requires sealants, while BSPP employs metal-to-metal or O-ring seals for closure. Threads are typically marked with "G" for parallel and "R" for tapered to aid in identification.

ISO Standard Connections:

Notable examples include ISO/DIS 6162 4-Bolt Flange and ISO 6149, which feature metric threads and utilize either metric or inch bolts. An "M" marking indicates the use of metric bolts. The sealing mechanism is similar to the SAE ORB, using O-rings compressed into a chamfer to ensure a tight seal.

German Connection Standards

DIN 7631:

This common metric style features a male connector with a straight metric thread and a 60° cone, with the seal occurring between the cone of the male and the tapered nose of the female flareless swivel.

DIN 3902:

This series includes a male connector with various female halves, such as compression style and flareless swivel types. The male has a 24° angle, and female options may include a DKO style O-ring.

DIN 3852:

Often used as a benchmark for connector and port designs internationally, DIN 3852 sets a standard controlled by German specifications.

Japanese Connection Standards

JIS Tapered Pipe (PT) and 30° Seat Connections:

These designs feature tapered and parallel threads similar to BSPT and BSPP, specifically adapted for Japanese standards. They are interchangeable with BSPT connections, demonstrating their versatility.

JIS 4-Bolt Flange:

Includes Type I Code 61 (standard series) and Type II Code 62 (6000 PSI series), featuring flanged heads with grooves for O-rings and threaded bolts that hold the connection securely.

Instrumentation Fittings

Double and Single Ferrule:

Instrumentation fittings are crucial for applications involving fluid or gas transfer in industries such as refineries and chemical plants. The double-ferrule version uses a two-piece mechanism that securely holds the tubing, while the single-ferrule version, though lacking a back ferrule, similarly achieves effective sealing.

Conclusion: Selecting and Maintaining Hydraulic Fittings

Selecting the right hydraulic fitting is crucial for ensuring the efficiency, safety, and integrity of hydraulic systems. This guide provides foundational knowledge to help navigate the complex landscape of hydraulic fittings across various global standards, emphasizing the importance of proper selection, installation, and maintenance.