Process of Elimination When Identifying Hydraulic Hose Fittings

Industrial machines and equipment are designed and manufactured in every corner of the world. The hydraulic systems alone use countless different types of fittings and adapters with different sealing methods and thread forms. While the sealing method can often be distinguished by appearance, thread forms all seem to look the same, making it difficult and time-consuming to identify them when equipment modifications or repairs are needed. Identifying a fitting can be easily done, however, through the process of elimination after uninstalling the fitting.

 

Hydraulic hose fittings can be one of two types – permanent or reusable. Permanent or crimped hydraulic fittings are widely used in the fluid power industry because they are easier and quicker to attach than reusable fittings. Crimped fittings are also more reliable. To attach a crimped fitting, you will need crimping or swaging equipment. These fittings are squeezed onto the hose at assembly and are discarded when the hose assembly fails. 

 

Reusable or field attachable hydraulic hose fittings are not commonly used today since they are considered "old technology."  A reusable fitting is easily identifiable because it fits right onto a hose by using only a wrench and a vise. Reusable fittings typically cost more than crimped fittings and are more time consuming during the assembly process.
 

Accurate identification of ports and connectors in a hydraulic system is necessary before the correct hose or tube assembly can be assembled and installed.

 

Port Connections	Tube/Hose Connections
NPT/NPTF BSPT (JIS-PT) Metric Taper SAE Straight Thread ISO 6149 JIS-B2351 DIN Metric BSPP (JIS-PF) 4-Bolt Flange	37⁰ Flare 30⁰ Flare (Metric) 45⁰ Flare 24⁰ Flareless (SAE) 24⁰ Flareless (DIN) 30⁰ Flare (BSPP) O-Ring Face Seal (ORFS) 60⁰ NPSM Swivel 60⁰ Cone (BSPP) 60⁰ Cone (Metric)

Types of hydraulic fittings vary depending on their sizes, configuration, and thread types. The three most common types of hose fittings are O-ring, mated angle and threaded. However, there are several more types of hydraulic hose fittings available.

 

O-Ring: The three types of O-ring seal designs are O-ring boss, flat face O-ring seal and O-ring flange. With these types of couplings, there is an O-ring seal that is the main component in creating the seal.

 

 

 

Mated Angle: An example of a mated angle is SAE 45° or JIC 37° but there are others as well. Fittings with an angle seat have straight or parallel threads for sealing. When the male and female counterparts are threaded together, the threads themselves do not actually form the seal. Instead, they function mechanically to bring the two mating angle seats together which ultimately forms the seal.

 

Tapered Threads: These types of fittings have two types of threads: male or female. Male fittings feature their threads on the outside and female fittings have threads on the inside. When the male and female counterparts are threaded together, the tapered threads deform which applies pressure on the couplings ultimately making a tight seal. Tapered threads can be imprecise but never use Teflon tape to ensure the seal. Teflon tape is often banned in hydraulic and pneumatic systems because of its tendency to shred and contaminate sensitive areas. Its lubricity has also been known to induce over-torquing. 
 

After you have determined the sealing method, visually look at the location of the O-ring, nose seat, seat angle and fitting termination. You can visually see the O-ring location as well as the type of nose seat. However, you will need to use a seat gauge to determine seat angle.  

 

O-Ring Location	Nose Seat	Seat Angle	Fitting Termination
Inside	Inverted	60⁰ Inclusive	British Standard Pipe Parallel
Inside	Inverted	24⁰ Inclusive	DIN 24⁰ Cone

 

O-Ring Location	Nose Seat	Seat Angle	Fitting Termination
In Flange Groove	Flat Face	N/A	SAE O-Ring Flange (Code 61 or 62)
Outside	Flat Face	N/A	SAE O-Ring Boss
At Nose Seat	Flat Face	N/A	O-Ring Face Seal

 

O-Ring Location	Nose Seat	Seat Angle	Fitting Termination
None	Standard	37⁰	JIC 37⁰ Flare
None	Standard	45⁰	JIC / SAE 45⁰ Flare
None	Standard	30⁰	Japanese Industrial Standard & Komatsu
None	Inverted	N/A	Metric Stand Pipe
None	Inverted	30⁰	National Pipe Straight
None	Inverted	45⁰	SAE Inverted Flare
None	Inverted	24⁰	Inclusive French Gaz 24⁰ Cone
None, except -20	Standard	24⁰	Inclusive French Gaz 24⁰ High-Pressure Flange

 

O-Ring Location	Nose Seat	Seat Angle	Fitting Termination
N/A	N/A	N/A	National Pipe Tapered
N/A	N/A	N/A	British Standard Pipe Tapered

 

 

With the caliper, measure the thread diameter of the largest point (Outside Diameter (O.D.) of male threads; Inside Diameter (I.D.) of female threads). Using the thread gauge, determine the number of threads per inch. Comparison of gauge and coupling threads against a lighted background will ensure an accurate reading.
 
Parker’s Hose Products Division has shadow images to easily determine thread, cone and hex size. Click on these images to print out a useful guide to assist in identifying hydraulic fittings. 
 

 

 

After you have determined the hydraulic hose fitting you need to replace, Parker Hannifin is an ideal supplier of choice. Parker offers the largest selection of hydraulic hoses plus more hydraulic fitting sizes than any other manufacturer. Parker’s Hose Products Division offers steel, brass, and stainless steel fittings from 3/16" to 3". Styles include O-ring face seal, flare, male pipe, metric designs and much more. Custom tube and hose fittings are also available in various configurations including NPTF, JIC, SAE, GAZ, ISO, DIN, JIS and BSP. Many manufacturers offer fitting wall charts as well to assist in the identification process.