Hydraulic hoses are often the last consideration in building a machine, even though they are often the factor most likely to blame when machines fail. The list below details some of the most common dangers to hydraulic hoses, and the products that are available to help protect them.
Abrasion occurs when the outer cover of a hydraulic hose becomes worn, exposing steel reinforcement wires and happens when the hose comes into contact with a metal edge or another piece of hose. The rubbing action occurs because the hose stretches and contracts as the pressure of the hydraulic oil inside the hose fluctuates and the hydraulic circuit changes functions. The standard rubber covers on hydraulic hoses wear quickly at contact points, causing many hose failures seen in the field.
Hose manufacturers developed abrasion-resistant products to overcome this issue. By adding polymers and plasticizers to the hose cover material, they were able to extend hose life dramatically. Early versions of abrasion-resistant covers were stiff and difficult to manipulate; now, advances in material designs have lead to abrasion-resistant hose covers with better flexibility than those for traditional hydraulic hoses.
For specific and severe points of abrasion, a plastic guard can be zip tied to the hose. By wrapping a heavy gauge plastic card around the hose and holding it in place with plastic ties, the piece acts as a buffer between the hydraulic hose and sharp edge. Another option for abrasion resistance is to install a nylon sleeve over the hose.
2. External Damage
Hydraulic hoses in mobile applications are exposed to very different dangers than in industrial applications. You likely wouldn’t expect a piece of rebar to rip through your injection molding machine, but hoses on excavators can experience threats such as rebar in every bucketful. In an attempt to protect hoses on heavy equipment, many contractors choose to have wire spring guards installed over their hoses. The heavy gauge plated steel coil is held in place between the crimp shells at each hose end. Although the spring does not make the hose indestructible, it does protect against debris and rocks encountered in construction applications.
This protection is also available as a flat steel coil, and now as a flat heavy gauge plastic coil. Plastic coils have the additional benefit of being able to be added to the hose after the ends have been crimped on. For extreme applications such as scrap grapple, a hose can be covered in full steel armor made of flexible plated steel or stainless steel hose crimped over the top of a rubber hydraulic hose. These covers protect against gouges in the cover which would expose reinforcement wires, leading to hose failure.
3. Failure at the Fitting
The place in which a hydraulic hose meets the crimp sell is one of the most common places for a hydraulic hose to fail. These failures are generally caused by the hose being bent too closely to the fitting due to improper routing or the weight of the hose. In order to support the hose at the crimp in applications where a bending force cannot be avoided, a bend restrictor can be installed on the hose at the crimp. Bren restrictors are rubber or plastic sleeves that cover the first six inches of hose after the crimp fitting. These sleeves are more resistant to bending than the hydraulic hose underneath, and therefore absorb bending force to protect the hose.
In applications where worker safety can be compromised by hose failure at the fitting (such as with hydraulic hand tools) a burst shield can be incorporated into the bend restrictor. Burst shields are steel or hard plastic sleeves that are built into bend restrictors in order to deflect a stream of oil from hose failure. By deflecting oil away from the operator, the risk of injection injury is reduced. Safety tethers are another safety feature that can mitigate the risk of hose failures at the fitting. These tethers attach to the hose and port fitting so that if a hose fails at the fitting, the tether will absorb the discharge force, keeping the hose from flailing and causing injuries.
4. Application Damage
Some applications pose specific dangers to hydraulic hoses. In the machine tool industry, hot chips pose a threat to hose covers. As such, this industry uses hydraulic hoses that possess an extra stainless steel braid cover. The braid is crimped under the fitting shell to stay in place. These covers provide protection against hot chips, but can fray from abrasion and become hazardous. Other temperature threats can be overcome by adding a fire-sleeve jacket over the hydraulic hose, which consists of a silicone jacket with fiberglass insulation to protect the hose from high-temperature machine parts.
5. Bad Routing
Many of the dangers posed to hydraulic hoses can be mitigated by properly routing the hydraulic hose. The addition of clamps along the length of a hose can keep the hose in a protected area and remove stress points. Plastic DIN block clamps are always available with smooth interior surfaces that are designed to hold hoses without damaging the covers. Plastic-dipped loop clamps can hold a hose out of harm’s way in extreme applications.
The proper choice of port fitting configuration can also help in reducing the stress on the hydraulic hose, and hydraulic swivels can be added to the ends of hoses to absorb movement and reduce flexing or twisting.
As you can see, there are many different types of threats to a hydraulic hose, and that for each specific danger, a specific solution can be found. Taking the extra time and cost to add the right protection pays off tenfold in the long run. Be sure to consult your hose manufacturer and local hose shop to be sure you are using the right product in the right application.
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