The Basics of Hydraulic Couplings –Threads and Seals for Fittings and Hoses

Hydraulic couplings, also known as fittings,play an important role to hydraulic equipment. Couplings are the devices that are used to connect the hoses to the hydraulic system. The hydraulic machinery will not be able to perform without a secure connection for the fluid to be pushed through. Generally couplings are made out of metal and are attached to hydraulic hose assemblies. There are two components to a coupling, a stem end and a thread end. The stem end attached to the hose and thread end is joined to the hose assembly and hydraulic equipment.Depending on the type of hose and fluid pressure passing through it, different coupling are used. There are a variety of ways to attach couplings when making hydraulic hose assemblies. Thread configurations on couplings come in two types: male and female. To establish conformity in the industry, thread ends were standardized. Today there are three principle types of hydraulic seals that thread end designs can conform to: thread seals, mated angle seals and “O-ring” seals. The first two use metal-to-metal contact to seal and the latter, “O” Rings, use a rubber-to-metal seal. The easiest couplings to install are ones used with low-pressure hoses. These couplings are simply lubricated and pushed into the hose end. As the hose tightens under pressure, the angled ridges on the coupling grip the hose. Hoses that are designed for high pressure use both reusable and permanent couplings.

Reusable couplings are attached to a hose using a ferrule. A ferrule is a collar that is screwed on over the hose cover using a wrench. The stem is wedged into the tube of the hose using threads on the ferrule. The compression of the hose between the stem and the ferrule holds the coupling on the hose. Once reusable couplings were the most prevalent coupling on the market, but permanent couplings have surpassed them in popularity. Hydraulic assembly-making equipment has made permanent couplings easier and faster to install. In general, permanent couplings cost less than field couplings.Permanent couplings require special equipment called “crimpers” in order to attach them to a hose and applies force perpendicular to the sides of the ferrule. As the coupling is crimped inward, serrations on the ferrule pierce the hose cover and dig into the wire reinforcement.Permanent couplings are available in both one-piece and two-piece configurations. One piece, couplings are pre-assembled and made with the ferrule permanently attached to the stem. Two-piece couplings consist of a stem and separate ferrule. When using two-piece couplings, it is important to match the ferrule with its appropriate stem and hose. Permanent couplings require for proper installation.