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Breakdown of Standard Hydraulic Hose & Fitting Sizes

It's important to know the specific type of hydraulic hose you're working with, because that will determine the fitting size which should be coupled with it, so that it attaches securely to whatever piece of machinery it's installed in. If there isn't a snug fit between the hose and the machinery, it could easily lead to leakage of the hydraulic fluid, and that will definitely cause a decrease in performance of your equipment, as well as a possible hazard. Making sure that you have the appropriate fitting for each of your hydraulic hoses will guarantee that this doesn't happen, and will allow your hydraulic equipment to perform up to its capabilities.

Importance of Hydraulics & How the Technology has Shaped Modern Life

Hydraulics has its origins back in the time of the Egyptians and Babylonians, who understood that the power of water could be harnessed to perform certain tasks. The first citizen of the world who gave serious thought to harnessing the power of water was the Greek Archimedes, who invented the hydraulic clock and the Archimedes screw, both of which were inventions far ahead of their time.

Unfortunately, hydraulics was overlooked by the world after the death of Archimedes, and was not revived again for a thousand years, when Blaise Pascal and Daniel Bernoulli developed principles which form the basis of modern hydraulics. The two biggest innovations in hydraulics were the pump and the self-contained hydraulic unit.

The pump was responsible for increasing pressure and the velocity of liquids well above the level found in nature, and the self-contained hydraulic unit made the whole operation very compact and consistent. Hydraulics are now used in a great many applications to generate massive amounts of power, and you'll find these types of systems in use on airplanes, spacecraft, automobiles, trains, ships, farming equipment, and a number of different machine tools.

How Do I Know Which Type of Hydraulic Part I’m Working With?

It's very important to accurately identify the various possible ports and connectors in any hydraulic system before choosing which hose to install in your system. If you were to choose parts which are not quite compatible with each other, it's very possible that you could have a leaking hydraulic system, and this would at a minimum, cause your hydraulic system to be inefficient in its performance.

In a worst-case scenario, it could even create a dangerous situation, because your heavy machinery might behave unpredictably and could even potentially injure workers on the scene. Here are some of the most common port connectors, and these can be identified by some of their distinguishing characteristics:

  • NPT/NPTF - NPT stands for National Pipe Taper, and it belongs to a set of standards issued by the American National Standard Pipe Thread Association, which is responsible for standardizing the screw threads which are used on pipe fittings and threaded pipes. NPT threads permit clearance on mating thread crests, but it does require a good seal to make it leak-proof, whereas NPTF does not.
  • BSPT (JIS-PT) - whereas NPT threads are standard in the U.S. and Canada, BSP threads are far more common in Europe, Asia, Australia, New Zealand, and many other countries of the world. While both threads have similar pitch with similarly shaped valleys and peaks, the NPT thread angle is 60 degrees, and the BSP angle is 55 degrees.
  • Metric Taper - metric taper pins function as fastening devices which are used in a number of different assemblies, including those in hydraulics systems.
  • SAE Straight Thread - these are straight thread fittings which accomplish the sealing function by positioning an O-Ring in between the wrench flats of the fitting and the thread itself. The O-Ring serves to provide a seal against the machined part of the female port, and this discourages the occurrence of thread stripping and the cracking or distorting of machine components, any of which will interfere with having a proper seal.
  • ISO 6149 - this document specifies dimensions for the metric ports used in adjustable and non-adjustable stud ends. This standard details the permissible working pressures to be used, and describes size, materials, design, and applications which are appropriate for use. It gives recommendations on stud ends and ports to be used for various designs in hydraulic fluid power applications.
  • JIS-B2351 - most JIS equipment has been specifically designed for use on machines which were manufactured either in Korea or Japan, and they function as hose adapters which use BSPP port connections. The B2351 is an 'O' port connection which is generally used in high pressure situations.
  • DIN Metric - the DIN designation refers to the German Institute for Standardization, and the metric style is the most common thread used throughout Europe.
  • BSPP (JIS-PF) - JIS adapters are generally designed with BSPP or BSPT port ends, and two different types of port ends, those being T4 and P4. The T4 port end has a 30-degree flare with BSPP threads, and the P4 port end has a 60-degree cone with BSPP threads.
  • 4-Bolt Flange - a 4-bolt flange block is known for having excellent mechanical stiffness and strength, along with dimensional stability. They also have strong resistance to any kind of corrosion or rust, and this makes them a good choice for hydraulic fluid systems.

What are the Most Common Fitting Sizes?

The most common fitting sizes in use today are those which are considered permanent or crimped. These are used widely in the fluid power industry because they can be attached much more quickly than reusable fittings can be. Permanent hydraulic fittings are also much more reliable than reusable fittings, and for these reasons, reusable fittings are now widely regarded as old technology, and are not as commonly used as their permanent counterparts.

Fitting sizes can generally be measured by using a thread gauge to measure inside diameter and outside diameter. It's fairly easy to obtain an accurate reading, by comparing gauge and coupling threads in a lighted background. The most common fitting sizes used today will generally fall into a relatively compact range, although there are some specialty fitting sizes which are also reasonably popular.

Replace Your Hoses and Fittings

If you are having trouble with your hydraulic system, you need to be able to work with a company who deeply understands custom hydraulic fittings and the system they are repairing. Contact Sapphire Hydraulics today, and our experienced technicians can be on your site quickly to get your machines back in working order.

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