Five Factors to Consider When Choosing Hydraulic Fittings
- Feb 03, 2018 -
Generally, however, when making hydraulic fitting connection choices today, there are five common end connections types that we use. They include:
JIC 37’ Flares: The Joint Industrial Conference (JIC) fitting is the most common hydraulic connection style. It consists of parallel threads and a 37’ cone on the fitting end that attaches to either a flared tube or hose fitting.
O-Ring Face Seals: O-ring face seal fittings have flat sealing surfaces that contain an embedded seal, which mates to flanged tubing or hose fittings. Flat sealing surfaces reduce the risk of over-torqueing, and the captured seal prevents leakage.
Inch Compression: The inch compression fitting is a bite type fitting for hydraulic tubing and there are very limited hose connections for this style. This fitting can be assembled onto hydraulic hard tubing in the field with minimal tooling required.
NPT Pipe Threads: NPT pipe threads are your traditional tapered thread fittings and have been used for 100 years. They are available in low-pressure black iron and brass, and high-pressure steel and stainless. This connection style is used in pneumatic and process systems, and lower-pressure hydraulic systems.
DIN Metric 24’ Bite Type: This is the most common hydraulic fitting style in Europe. As such, there is a full line of hose fittings for this style, and it can be used with metric-sized tubing. Newer versions of this fitting style incorporate a captured elastomeric seal on the mating surface, providing better sealing and reusability.
Now that we have defined common types of hydraulic fittings, let’s consider the five factors you should consider when selecting the right fitting for your application:
Versatility. JIC fittings offer the best versatility of any of the aforementioned fitting systems. Additionally, there are available fittings that can connect JIC fittings to any foreign or American port, and jump sizes can expand or reduce between any sizes. A key benefit of JIC is the great variety of product that is typically stocked by vendors, including straights, elbows, long drops and male or female threads.
Availability. JIC and NPT fittings have been the field standard for decades, and they are readily available in both volume and variety. As a growing number of OEMs converts to O-ring face seals and DIN metric fitting styles, any hydraulic hose shop should be able to identify these new fittings, but the selection may be limited.
Pressure Rating. Many OEMs are choosing O-ring face seals and DIN metric fittings, as required pressure ratings have increased. JIC fittings are not rated for these pressure ratings, especially in high vibration applications. Similarly, NPT threads are not recommended for higher pressure (except inexplicably in 10,000psi static hydraulic systems). These applications require specially-rated fittings.
Application. The application in which a fitting will be used is a critical factor in choosing the right fitting. The old STAMP acronym applies to fittings as well as it does to hose. Size, Temperature, Application, Media and Pressure all must be taken into consideration when making this choice. Each fitting style has limiting factors such as the temperature rating of a seal, or the pressure rating of a shape. Manufacturer specifications are published in catalogs, and special attention must be paid to the ratings, as they change by size, material and shape. For example, a JIC fitting might be rated to 6,000psi in 3/8”, but only 2,000psi in 2”. Some hose ends are rated to lower pressure than the hose to which they are attached; in those cases the entire hose is de-rated to the lower pressure.
Reliability. NPT pipe threads have always been popular, as leaks can be fixed by simply tightening the fitting. This practice, however, has led to cracked fittings and permanent connections. NPT’s reliance on Teflon tape and dope raises the risk of contamination in the hydraulics, which is unacceptable in the tight clearances of today’s systems. While JIC has been the industry standard for years, it still susceptible to cracked flares from overaggressive wrenching. The mated sealing surfaces in O-ring face seal fittings and DIN metric fittings reduce the risk of over torqueing, and provide greater reliability due to the elastomeric seal that is captured in the mating surface.
At the end of the day, all fittings are only as good as assembler who installed them. There are proper assembly procedures for each of the fitting styles, and strict adherence to those steps makes the difference between a solid connection and a problem waiting to happen.
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