Joyce Laird • Contributing Editor
When looking at a full hose assembly, it is basically a length of hose with a properly attached fitting on each end. Robert J. Koehler, Sr. Training Specialist at Eaton Corporation, explained that a hose assembly is composed of the hose and the end fittings, which are determined by the application in which the hose assembly is going to be placed.
Hydraulic hoses have three major components, he said, which include the following:
- Tube: The tube is the inner-most portion of the hose. Its role is to convey the media from one end of the hose to the other and protect the outside from the media or fluid being conveyed.
- Reinforcement: The reinforcement is the strength of the hose and comes in a variety of types, including braided, spiral and helical.
- Cover: The cover is designed to protect the reinforcement and tube from the outside environment.
“Each of these three components plays an important role to allow the hose to work in a variety of environments,” Koehler added. “These hoses are designed to meet different specifications and requirements that arise with the different environments where hoses will be installed.”
“Fittings are usually made of metal, such as carbon steel, stainless steel, brass and so on. Within these fittings there are two major components,” he continued.
Fitting components are comprised of the following:
- Socket: The socket is the portion of the fitting that goes over the outer cover.
- Stem: The stem is the portion of the fitting that goes directly into the I.D. of the inner tube of the hose. It extends out of the hose and into the connecting end. The connecting end of the fitting is the portion of the fitting that allows the hose to connect to other components.
Like hoses, fittings have to meet various specifications and are usually designed to fit a specific hose. The hoses and fittings are typically designed to be a matched set. It is important to refer to the manufacturers recommended hose and fitting combinations for proper assembly and application, Koehler said.
“Lastly, the hose and fitting need to be assembled using the recommend procedures and proper equipment. When attaching a hose fitting permanently to the hose it is important to use the proper method and always check the completed assembly for proper crimping/swaging, specifications and overall length for the application.”
As Koehler discussed earlier, every hose is made up of a tube, reinforcement and cover. Each of these components must be compatible with the media, or product, flowing through the hose. Every hose lends itself to a specific application, including the media flowing through it.
“Because hydraulic hoses can support a variety of materials, the tube material needs to be selected based on the type of hydraulic fluid being used in the equipment. The fittings must also be compatible with the fluid. Anytime you have an improper combination of fluid and components, you risk the possibility of hose failure. This happens when the tube material softens and leads to a leak or the hose end blows off. Sometimes, you will see a leak and catch it early, but leaks aren’t always visible,” Koehler warned.
He went on to explain that if there is leak and a product can’t be contained, it can effuse through the tube, causing the hose to swell. Because of the reinforcement, the tube can swell inward, reducing the tube I.D. and increasing the velocity of the media. This can cause the tube to start pulling apart, with no exterior visual signs, eventually leading to system failure or even hose end blow-off.
“A mismatch of fluids and components can also lead to a third hole, which can occur when a hose is placed into an application it is not intended for. For example, putting a 3,000 psi hose into a 5,000 psi application. This over pressurization of the hose will cause a leak to open, creating a ‘third hole’ in the wall of the hose,” he said. “The bottom line is that overall, improper tube material fluid match would cause the life expectancy of the hose to be significantly reduced.”