FLUID POWER HANDBOOK
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HYDRAULIC
FITTINGS & FLANGES Hydraulic fittings connect conductors such as hoses, pipes and tubes to the components in a hydraulic system. They allow the pressurized fluid to move through the system without leakage. Available in a variety of styles to change and direct, change or split flow, most fittings have a male and female component that join to form a connection. They can be manufactured as unions, plugs, crosses and elbows. It is critical to carefully identify threads on the fitting connections, as these threads can look almost identical from one standard to another. However, because they are not mates, they will not properly engage. In addition to reviewing documents from SAE, NFPA and ISO to help identify each standard to confirm diameter and thread type, keeping thread identification kits on hand can help with this concern. Fitting connection types include: welded (socket weld, butt weld, slip on); threaded (NPTF, BSPT [both not recommended but used], SAE straight thread, ISO 6149; BSPP); flanged; barbed; quick-disconnect; push-to-connect; 37˚ flare; 24˚ cone; and inverted flare, among others. When selecting a type of fitting, some important considerations are working pressure, vibration, type of fitting, desired attachment, size of piping, flow, material of the conductor or component, and price. The fluid power industry is trying to transition to fittings with an elastomeric seal — generally O-rings — to prevent leakage. These include, but are not limited to, the SAE straight thread, face seal, ISO 6149, and SAE J518 (Code
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Hydraulic Fittings & Flanges 7-19_FPW Vs3.indd 26
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61 and Code 62) flanges. Seal construction must be compatible with the type of fluid being used in the system, although very few applications require anything other than Buna Nitrile or Viton. When selecting a fitting, several considerations are important. Most non-flanged fittings have a gender — called male and female — that are joined together to form a union. Most fittings are sized based on the size of the conductor (size of hose, pipe or tube), and overall dimensions can vary greatly based on fitting type, even for the same size conductors. Additionally, most fitting types are available in a multitude of materials, including plastic, brass, steel, stainless or specialty metals like Monel. Each are applied in applications based on the fluid medium and ambient conditions, and each has different performance characteristics that allow customization within a fitting type. Often the first choice is to match the fitting to a similar material of the conductor or component that it is connecting to: plastic to plastic, steel to steel and stainless to stainless. www.fluidpowerworld.com
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