Hose manufacturers each use a diverse range of materials that can result in a variety of hose styles. They design their hose and coupling components to fit their own tolerances. Hoses from various manufacturers may have similar dimensions and constructions, but different rubber compounds and reinforcement materials make a huge difference when it comes to hose failures and every manufacturer's "recipe" is unique.
Fundamentals of hose design have not changed with the introduction of new and improved component materials. Hose consists of three basic elements which are the inner tube, reinforcement, and the outer cover—with each serving a primary function.
The inner tube is the innermost component of the hose, which gives the hose its chemical compatibility characteristics. The inner tube must have some flexibility and needs to be compatible with the type of fluid it will carry. For Parker Hose Products Division, we commonly use compounds such as PKR rubber, synthetic rubber, butyl rubber and EPDM rubber. Each compound can react differently to the media being conveyed. For instance, EPDM is a base polymer used to make rubber hoses. It is a high-density synthetic rubber compatible with fireproof hydraulic fluids, ketones, hot and cold water, and various alkalis. EPDM hoses resist heat, ozone, and weather, and maintain excellent flexibility at high and low temperatures.
A second commonly used chemical is a nitrile-based polymer which is a synthetic rubber copolymer of acrylonitrile (ACN) and butadiene. Nitriles provide good compatibility with oils and standard hydraulic fluids. The higher the ACN content, the more resistant the hose is to fluids, but the worse it will be for low temperature flexing, which can lead to cracking and failure as the hose flexes when it is below its stated operating temperature.
The reinforcement layer surrounds the inner tube and gives the hose strength and the ability to hold pressure. The amount and type of reinforcement determines the pressure rating of hose. The reinforcement layer consists of one or more sheaths of braided wire, spiral-wound wire, or textile yarn.
The outer layer or cover is the outermost component of hose that protects the reinforcement from abrasion, corrosion, chemicals and ozone/U.V. The outer layer is often weather-, oil- or abrasion-resistant depending upon how the manufacturer designed the hose for specific environments. For instance, Parker hoses come in a variety of cover options so you can match the right cover to your application. Our ToughCover is 80 times more abrasion resistant than our Standard cover, while our SuperTough cover is 450 times more abrasion resistant offering unparalleled protection from abrasive environments.
Even though the construction of hydraulic hose is very similar across all manufacturers, the exact recipe is a critical component to the performance and the hose life. Each manufacturer has their own proprietary method regarding the chemistry behind each hose. Putting designs to the test is key to creating hoses specifically designed for each application.
The chemistry for hoses is chosen based on what they are going to be used for, but the goal for all hoses is the same – maximum durability, high flexibility and long service life.
Parker's materials development laboratory uses the latest technology in equipment and methods to evaluate the behaviors of elastomeric materials under varying conditions. Our in-house capability assures the materials in our design are engineered to withstand the extremes of application and the environment time after time, every time.
Article contributed by Kyri McDonough, marketing services manager at Hose Products Division, Parker Hannifin.
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