There are more reasons why a hose will fail than we can discuss here, so we will discuss the top five hose failures and how to prevent them. Remember, as discussed in the previous lesson, that most hydraulic hose failures can be avoided by regularly checking the system.

Abrasion:

Abrasion due to rubbing against another hose or part of machinery is the number one reason why a hose will fail. Although most hoses have a tough protective outer layer, if the hose continuously rubs over time, it will wear the protective layer thin, which is an integral part of the hose that helps maintain the high pressure. Often, these situations are unavoidable, but that doesn't mean there are ways to protect the hose in these situations.

Protection:

The hydraulic hose industry realized the abrasion problem and came up with several solutions to help extend the life of a hose due to rubbing.

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Steel Protective Coil Spring:

The most common of these solutions will be the steel coil spring. The spring is a good solution for keeping your hose from rubbing against a flat, smooth surface. Due to the wide gap of the individual coils, this option allows for the bend radius of a hose and ample flexibility. However, using the spring coils on a rough surface or around sharp corners will catch, stretch, and possibly break, putting extra stress on the hose and connections.

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Steel Protective Coil Sleeve:

The protective sleeve is like the spring, except the sleeve covers more of the hose with more comprehensive coils. These wider coils are less likely to get caught on flat, rough surfaces but will still get hung up on corners like the spring coil cover. The disadvantage to these protective coils is that they are less likely to break but more likely to rip and bend, which means these rips and bends could be forced into the hose and cut or deform the outer later—leading to less life of your hose. Also, due to the wide coil, the bend radius is severely reduced.

The same type of coil sleeve is also available in a rigid plastic; if it gets hung up, rips, or bends, it will not damage the hose. However, the disadvantage is if it continuously rubs over a flat, rough surface, it will not last as long as a steel sleeve. Coil sleeves are also available in stainless steel.

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Nylon Abrasion Sleeve:

A nylon abrasion sleeve is an excellent choice for all the above situations. The nylon sleeve covers 100% of the hose. Allows maximum bend radius. Will not get hung up on corners and rough flat surfaces. A nylon sleeve is excellent for bundling hoses together. Unlike the coil and spring covered, which require a more precise fit to the outside diameter of the hose, the nylon fit is less critical.

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Improper installation:

Incorrect installation practices, such as insufficient or excessive tightening of fittings, bending the hose below its minimum bend radius, or using incompatible fittings or hoses for the application, can weaken the hose assembly and cause failure.

Incorrect installation:

Over-tightening of the fitting or adapter will lead to immediate hose failure. From the above picture, the JIC fitting is over-tightened and caused the 37-degree angle to crack and split. As you can imagine, it fails as soon as the system is charged.

As over-tightening causes damage, not tightening a fitting enough can also lead to a damaged hose. If under-tightened when the system is charged, the pressure can blow the fitting from its connection; not only will you get a horrific mess, but if someone is close, the hose will whip around like an air hose and cause someone to get seriously injured. In addition to the possibility of injury, the threads could be damaged when the fitting blows off, rendering the fitting and adapter useless and leading to costly repairs.

To ensure proper tightening, first, ensure you align the fitting with the correct port and hand tighten the fitting as far as possible; if aligned correctly, the fitting should finger tighten easily. Complete the assembly by tightening it to the recommended torque value.

Fluid Compatibility:

Incompatible fluids or additives can degrade the hose material over time, leading to loss of flexibility, cracking, or deterioration of the inner tube. Fluid contamination, such as water, dirt, or debris, can accelerate wear and compromise hose integrity.

All hydraulic hoses are identified by the inner tube, which we will cover in more detail in "Identifying Hydraulic Hose" later. For now, we will talk about the basics. The inner tube of a hydraulic line is like the veins in your body that convey blood to every part of your body. If the wrong blood type is put into your body, it will reject the fluid, and the body will begin to fail. The same goes for a hydraulic line; the inner tube of a hydraulic line is designed for a specific type of fluid. If the wrong fluid is pipped through a hose not designed for that particular fluid, it will begin to break down and eventually fail.

High Pressure and Temperature:

Operating hydraulic systems at pressures or temperatures beyond the hose's design limits can cause the hose to weaken, soften, or harden, increasing the risk of burst or leakage. Thermal cycling and pressure spikes can further exacerbate these effects.

One of the most essential rules of hydraulic lines is that the highest pressure rating of a hose is the slightest pressure of the components. In other words, if a hose is rated for 5,000 psi but the fitting is rated for 3,000 psi, then the assembly's WP (working pressure) is 3,000 psi.