While there might be hundreds if not thousands of hydraulic fittings and connectors, they all boil down to three basic types. These three types are either metal seal, soft seal, or tapered thread connectors. No matter which of these types of fittings yours belongs to, it will be required to satisfy two conditions: it must seal and it must hold.
In some cases, the same mechanism can fulfill both functions, and in other cases, two different parts of the same mechanism will handle the necessary functions. Tapered pipe connectors are cut on a taper with a pipe's diameter, and it changes along the entire threaded portion of a pipe, in order to make the connection tighter. These types of fittings require a sealer, so you can be sure there will be no leakage around the fitting, and this is usually accomplished with a chemical sealant or a tape sealant.
While it might be difficult to orient the tapered pipe threads correctly, it's very important to do so, because a poor seal might result in leakage when pressure is applied. If there is a disadvantage to tapered pipe connections, it's that they must be either soldered or welded to tubes when making a connection.
Metal seal connectors were invented largely to provide an alternative to tapered pipe thread varieties. This type uses a tapered thread combined with a machined face, to provide a seal capable of handling the typical high pressure associated with hydraulics. The thread helps to accomplish the holding power, while the sealing is managed by the machined face.
These kinds are easier to orient than a tapered connector, and they generally provide a better seal, without the need for any kind of additional sealant. However, they do still require welding or soldering to the tube. Soft seal are probably the most popular type used today, and these have an elastomeric seal that prevents leakage even under high-pressure situations.
One of the big advantages to using soft seal connectors is that they can be installed very quickly, and this is highly advantageous in industrial applications. They are also capable of resisting heavy vibrations which many systems are subject to, so they don't break down nearly as frequently.
It's not a difficult process to measure for the correct hydraulic fitting, and it's extremely important that you do so. Fittings and hoses which are an apparent match can be just a tiny bit off, and that will always lead to a hydraulic leak that can shut down your operation. The information below will help you to go through the measurement process quickly and efficiently, so as to avoid any possible leakage issues.
Tools:
1) ID/OD calipers
2) Thread pitch gauge, used to place the gauge teeth on the threads, until you see that there's a tight fit.
Make sure there is no gap between the fitting and the gauge teeth. If your fitting is somewhat worn, it might be difficult to obtain a match, so you're better off to work with newer fittings. Most manufacturers of fittings provide thread identification guides on their websites or in brochures that come with the products, so all you have to do is match the relevant charts to the actual thread measurement.
Measuring the Outer Diameter of the thread – place the ID/OD caliper around the threads so as to obtain a snug fit.
Measuring the Inner Diameter of the thread – insert the caliper into the fitting so you can obtain the correct measurement, and match it to the data charts provided by the manufacturer.
Determine if yours is parallel or tapered.
