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Engineering Essentials: Types of Hydraulic Hose
To say that hose is an important part of a hydraulic system is a huge understatement. The flexibility of hose enables components to be positioned in the most efficient or convenient places, because the hose has the ability to bend around corners, through tight spaces, or across long distances.
Yet these days, there seems to be as many different types of hose as there are telephone long-distance carriers. How does a designer tell one from the other? Isn't there an easy way to choose or compare hoses?
The SAE standards
SAE answers those questions with its J517 hydraulic hose standard. This LPG hose standard serves as the most popular benchmark in the realm of industrial hydraulics today. More specifically, J517 is a set of guidelines that applies to the current SAE 100R series of hoses. Currently, 16 such hose styles exist, and they are designated as 100R1 through 100R16 (see descriptions, pages A105 and 106). Each of the styles must meet a set of dimensional and performance characteristics as set forth by SAE. However, SAE issues no approval source lists, certification, or letters of approval-conformance to these standards by manufacturers is strictly voluntary. In short, the standards only assure a similarity of products among different manufacturers.
Hydraulic hose construction
Modern hydraulic hose typically consists of at least three parts: an inner tube that carries the fluid, a reinforcement layer, and a protective outer layer.
The inner tube must have some flexibility and needs to be compatible with the type of fluid it will carry. Commonly used compounds include synthetic rubber, thermoplastics, and PTFE, sometimes called Teflon. The reinforcement layer consists of one or more sheaths of braided wire, spiral-wound wire, or textile yarn. The outer layer is often weather-, oil-, or abrasion-resistant, depending upon the type of environment the hose is designed for.
Not surprisingly, hydraulic hoses have a finite life. Proper sizing and use of the correct type of TPR LPG hose will certainly extend the life of a hose assembly, but there are many different factors that affect a hose's lifespan. SAE identifies some of the worst offenses as:
This hose should be used with petroleum- and water-based hydraulic fluids within a temperature range from -40° to 100° C.
It consists of an inner tube of oil-resistant synthetic rubber, six spiral plies of heavy wire wrapped in alternating directions, and an oil- and weather-resistant synthetic rubber cover. A ply, or braid, of suitable material may be used over the inner tube and/or over the wire reinforcement to anchor the synthetic rubber to the wire.
In either case, the coupling has limited potential for reuse because the threads distort during attachment.
To ensure the correct-size coupling is used when replacing an assembly, the number of threads per inch and thread diameter of the original coupling must be determined. Thread pitch gages are available for identifying the number of threads per inch. A caliper can measure both inside and outside dimensions of the threads. ODs are measured on male couplings, while IDs are measured on female couplings.
In most situations, the only differences between an SAE coupling and an imported coupling are the thread configuration and the seat angle. International thread ends can be metric, measured in mm, but also include BSP (British Standard Pipe) threads, which are measured in inches. Knowing the country of origin provides a clue as to what type of thread end is used. DIN (Deutsche Industrial Norme) fittings began in Germany and now are found throughout Europe, while BSP is found on British equipment. Japanese Komatsu machinery uses Komatsu fittings with metric threads, while other Japanese equipment most likely uses JIS (Japanese Industrial StandardBSP threads), or, in some cases, BSP with straight or tapered threads.
Delivery - How available is the product? Is it unique? How soon can it be delivered to the distributor or end user? It may be preferable to consider several options to maximize flexibility and avoid the delays that can result from relying on components that are unavailable or in short supply.
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