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Engineering Essentials: Types of Hydraulic Hose
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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.
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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?
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The SAE standards
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SAE answers those questions with its J517 hydraulic hose standard. This <a
href="http://www.chuanhseng.com/lpg-hose/" target="_self">LPG hose</a> 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.
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Hydraulic hose construction
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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.
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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.
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Not surprisingly, hydraulic hoses have a finite life. Proper sizing and use of the
correct type of <a href="http://www.chuanhseng.com/lpg-hose/tpr-lpg-hose/"
target="_self">TPR LPG hose</a> 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:
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flexing the hose to less than the specified minimum bend radius
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twisting, pulling, kinking, crushing, or abrading the hose
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operating the hydraulic system above maximum or below minimum temperature
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exposing the hose to rapid or transient rises (surges) in pressure above the maximum
operating pressure, and
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intermixing hose, fittings, or assembly equipment not recommended as compatible by the
manufacturer or not following the manufacturer's instructions for fabricating hose
assemblies.
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Selecting the proper hose
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Here are seven recommended steps the system designer should follow during the hose and
coupling selection process. To help determine the proper hose for an application, use the
acronym STAMPED - from Size, Temperature, Application, Materials, Pressure, Ends, and
Delivery. Here is what to consider in each area:
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Size - In order to select the proper hose size for replacement, it is important to
measure the inside and <a href="http://www.chuanhseng.com/natural-gas-hose/"
target="_self">natural gas hose </a>diameters exactly using a precision-engineered
caliper, as well as the length of the hose. Hose OD is particularly important when hose-
support clamps are used or when hoses are routed through bulkheads. Check individual hose
specification tables for ODs in suppliers' catalogs. When replacing a hose assembly,
always cut the new hose the same length as the one being removed. Moving components of the
equipment may pinch or even sever too long a hose. If the replacement hose is too short,
pressure may cause the hose to contract and be stretched, leading to reduced service life.
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Changes in hose length when pressurized range between +2% to 4% while hydraulic
mechanisms are in operation. Allow for possible shortening of the hose during operation by
making the hose lengths slightly longer than the actual distance between the two
connections.
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Temperature - All hoses are rated with a maximum working temperature ranging from 200
° to 300° F based on the fluid temperature. Exposure to continuous high temperatures can
lead to hoses losing their flexibility. Failure to use hydraulic oil with the proper
viscosity to hold up under high temperatures can accelerate this problem. Always follow
the hose manufacturer's recommendations.
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Exceeding these temperature recommendations can reduce hose life by as much as 80%.
Depending on materials used, acceptable temperatures may range from -65° F (Hytrel and
winterized rubber compounds) to 400° F (PTFE). External temperatures become a factor when
hoses are exposed to a turbo manifold or some other heat source.
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When hoses are exposed to high external and internal temperatures concurrently, there
will be a considerable reduction in hose service life. Insulating sleeves can help protect
hose from hot equipment parts and other high temperature sources that are potentially
hazardous. In these situations, an additional barrier is usually required to shield
hydraulic fluid from a potential source of ignition.
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Application - Will the selected hose meet bend radius requirements? This refers to the
minimum bend radius (usually in inches) that a hydraulic hose must meet. Exceeding this
bend radius (using a radius smaller than recommended) is likely to injure the hose
reinforcement and reduce hose life.
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Route high-pressure hydraulic lines parallel to machine contours whenever possible.
This practice can help save money by reducing line lengths and minimizing the number of
hard-angle, flow-restricting bends. Such routing also can protect lines from external
damage and promote easier servicing.
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Materials - It is mandatory to consult a compatibility chart to check that the tube
compound is compatible with the fluid used in the system. Elevated temperature, fluid
contamination, and concentration will affect the chemical compatibility of the tube and
fluid. Most hydraulic hoses are compatible with petroleum-based oils. Note that new
readily biodegradeable or green fluids may present a problem for some <a
href="http://www.chuanhseng.com/natural-gas-hose/csa-natural-gas-hose/" target="_self">csa
natural gas hose</a>.
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