Hydraulic hose fittings play a crucial role in connecting different conductors, like tubes, pipes, and hoses, within a hydraulic system. These fittings typically have a male and female part to ensure a secure connection. Their main functions are to guide fluid flow, prevent leaks, and maintain pressure.
Different types of fittings give designers the flexibility to alter fluid flow, divide it, or adjust the positioning of the lines. Here’s a simplified overview of common hydraulic hose fitting sizes and types used by professionals:
American Connections: National Pipe Tapered Fuel (NPTF)
NPTF connectors have both male and female threads. When these threads are joined, they form a tight seal due to the deformation of the threads. This is often referred to as a “dry seal thread.” For an even tighter seal, you can use teflon or pipe dope. Although the National Fluid Power Association (NFPA) doesn’t recommend NPTF for hydraulic systems, it’s still commonly used in fluid piping setups.
It’s important to note: NPTF and BSPT connectors might look alike, but they aren’t interchangeable.
National Pipe Straight Mechanical (NPSM)
NPSM connectors have straight threads on both the male and female ends. The male end features a 30° internal chamfer, while the female end has a complementary inverted 30° seat. When these two ends are joined, they form a mechanical connection. This tapered seat design ensures a leak-proof bond, making NPSM connectors popular in fluid power systems.
It’s worth noting: A female NPSM can effectively seal when paired with a chamfered male NPTF.
JIC 37° Flare (SAE J514)
Commonly used in hydraulic systems, the JIC 37° flare connectors have both male and female parts with a 37° flare seat and straight threads. When connected, the flare seats of both parts seal together, while their straight threads provide the mechanical bond.
It’s important to highlight: Even though many SAE J514 threads may resemble SAE 45° flare threads, their seating angles are different.
SAE 45° Flare (SAE J512)
SAE 45° flare connectors are commonly used in low-pressure settings such as refrigerant and fuel lines, and in automotive piping. Both parts of this connector have a 45° flare seat. When connected, their threads interlock to create a strong mechanical bond, with the seal forming at the 45° flare seat.
Keep in mind: While SAE 45° flare connectors might look like JIC 37° flare connectors, the difference lies in the seating angles.
SAE Straight Thread O-ring (O-Ring Boss) – SAE J1926-1 and ISO 11296-1
The O-Ring Boss female port features a sealing face, a chamfer, and straight threads. On the other hand, the male connector comes with an O-ring and straight threads. The connection is sealed when the O-ring fits snugly into the chamfer. The interlocking of the male and female threads ensures a robust mechanical bond. This type of connection is frequently used in high-pressure hydraulic systems.
O-Ring Face Seal (SAE J1453)
The O-Ring Face Seal connection offers excellent leak protection and is suitable for applications reaching up to 6000 psi. The male part features an O-ring and straight thread, while the female counterpart has a flat machined surface and straight thread. The seal is formed when the male’s O-ring presses against the flat surface of the female part. The connection is secured by the swivel nut on the female side.
SAE Inverted Flare (SAE J512)
Common in automotive systems, the SAE Inverted Flare connection has a male connector with a 42° seat and a flared male tubing at a 45° seat. The female part offers a 42° seat, which serves as the sealing surface. When connected, their threads interlock, ensuring a sturdy mechanical bond.
British Standard Pipe Parallel (BSPP)
The male part of the BSPP connection features a 30° seat. The female swivel’s tapered nose seals against this seat.
It’s important to note: While the male end might resemble the American National Pipe Straight Mechanical (NPSM) male, they aren’t interchangeable because of their distinct thread pitches.
British Standard Pipe Tapered (BSPT)
The BSPT connection involves a tapered male end that fits into a tapered female end, with the seal created within the threads.
It’s crucial to understand: While the BSPT male might look similar to the National Pipe Tapered Fuel (NPTF) male, they can’t be swapped out for each other because of differences in size and thread shape.
Metric Tube Compression (DIN 2353 24° Cone)
The male part of this connection boasts a 24° cone and straight thread. In contrast, the three female connectors come with straight threads and a sealing surface. The connection is sealed when the male cone aligns with the sealing areas of the female connectors.
These fittings come in two types: DIN 2353 L (light) and DIN 2353 S (heavy). Each type corresponds to specific tube sizes and thread dimensions, as outlined in the subsequent table:
Japanese Industrial Standard JIS 30° Flare
The male component of this connection features a 30° seat and straight thread. Similarly, the female part has a 30° seat with a straight thread. While this connection might resemble the 37° Flare, its 30° seat and thread dimensions, which are similar to BSPP, set it apart from the American 37° Flare.
Komatsu 30° Flare (JIS Metric)
The Komatsu 30° Flare connection features parallel metric threads along with a 30° seat, making it a standard choice for Komatsu equipment. Although it bears resemblance to the JIS 30° flare, the latter’s thread dimensions are more akin to BSPP.
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