Hydraulic hoses are an often-overlooked part of hydraulic maintenance, but they are critical to the efficient and safe operation of your machine. If hydraulic fluid is the lifeblood of your machine, then hydraulic hoses are the arteries of the system - containing and directing the pressure to do its work. But they’re also equally dangerous if poorly maintained. Damaged hydraulic hoses are the main cause of accidental injection, which causes severe injuries to workers. And, as you can imagine, hydraulic hoses that fail while the machine is in operation ould lead to catastrophic results if a load were to fall at an inopportune time.
So, for the health of your machine and your people, it’s important to understand the common causes for hydraulic hose failure and know how to intervene and maintain hoses to keep them in good condition. With that in mind, here are some of the most common reasons for hydraulic hose failure and how to protect against them.
WHAT CAUSES HYDRAULIC HOSE FAILURE?
Tube erosion is characterised by a breakdown of the inner surface of the hydraulic hose and is usually caused by either persistent high velocity fluid flowing through the tube, or fluid that is contaminated by small particles.
High fluid velocity can be caused by using a hydraulic hose that is too small. Small orifices accelerate fluids (think of the way the stream from a garden hose is increased when you hold a thumb over the hose mouth). In some cases, tight bends in the hydraulic hose can produce this effect and also cause fluid acceleration, which leads to excessive erosion at this point.
Fluid that is contaminated with small particles is another source of erosion - acting like sandpaper moving past the inner surface of tube, breaking it down and wearing it away. Eventually, this will lead to weak points and eventual failure. This is another reason to change hydraulic fluid filters regularly and keep an eye on contamination levels at all times.
Overheating will cause the hose to become stiff and brittle. Heat causes the elastomer material to break down and lose its flexibility over time. The inner tube will also harden and begin to crack because the plasticisers in the elastomer will break down or harden under high temperatures.
The outer cover may appear cracked and dried out, or blackened. The hose assembly may retain its shape once removed from the machine and and you will see and hear cracking if you attempt to flex the hose.
To avoid heat-hardening, review the application and either replace the hose with that of a higher heat rating, or take steps to reduce the temperature to which it is exposed. Installing shields or heat guards will help protect against ambient heat. In the case of high fluid temperature, consider installing a heat exchanger or adapting the system design itself.
Abrasion is a very common enemy of hydraulic hoses, especially in hard working environments where machines perform hundreds of cycles every day. Hoses that come into contact with other machine surfaces will inevitably encounter some form of abrasion. Contact with moving parts and sharp edges will obviously encounter extreme abrasion very quickly, but even subtle vibrations can have an abrasive effect. Over the course of weeks and months these can have a significant effect on the hose integrity. Eventually, the hose cover will be worn away, exposing the reinforcement layers. At this point, the hose is no longer fit for duty. For this reason, it’s very important to consider the way in which your hoses are routed to avoid the worst potential abrasion situations. Where contact is unavoidable, special reinforcing hose guards can be used to beef up these areas.
If a hose blows out in a very clean fashion with no signs of abrasion, it is likely that the hose experienced more pressure than it was designed to cope with. In this case, review the application and either reduce the working pressure below the maximum pressure rating for the hoses or replace the hose with one which has a higher working pressure.
Incompatible hydraulic fluid
Not all hydraulic fluid is compatible with all hose types. Depending on the application, hydraulic fluid must perform in different ways and thus, the chemical makeup of hydraulic fluid types can differ quite radically. Certain types of hydraulic fluids react chemically with certain types of elastomers - of which hydraulic hoses are made.
Incompatible fluids will cause the inner tube of the hose to deteriorate, swell, and delaminate. This is particularly dangerous since it’s not always apparent that this is happening from outward observation. Meaning hoses can fail suddenly and without warning.
Never use hydraulic fluid without checking the compatibility with the hoses. To be safe, you must ensure the fluid is not only compatible with the inner tube, but also the outer cover, fittings, and the o-rings. Mixing incompatible fluids is also a no-no.
Exceeding minimum bend radius
While hydraulic hoses are flexible, they all have a limit beyond which they should not be bent. Exceeding the minimum bend radius can cause buckling, kinks and blockages, which can easily overpressure the hose and cause a blow-out failure. Even minor excessive bend radius can create a wear point in a machine where vibrations magnify at that point.
To prevent failures, check the hose length and routing to ensure it does not result in tight turns that exceed the minimum bend radius as prescribed by your hose manufacturer.
Improper assembly is another cause of hydraulic hose failure. If the hose fitting is not seated deeply enough and crimped and secured properly, high operating pressure will quickly reveal this as a weak-point. Resulting in leaking fittings or blown-off hoses.
In addition, when hoses are cut to size, they must be carefully cleaned and flushed to prevent contamination by abrasive debris that is left behind. Abrasive debris left in the hose will contaminate the hydraulic system and lead to small fractures that damage the inner tube of the hose assembly. Thus, the inner tube should be as clean as possible, and the ends of the hoses should be clamped after the fittings have been crimped into place.
Exceeding hydraulic hose maximum service life
Hydraulic hoses endure a torturous life and are subjected to extreme pressures during the course of their duties. As such, they are subject to stretching, fatigue and eventually failure. Thus, it’s important to be aware of the age of your hydraulic hoses and replace them before they reach the maximum service life for the application.
Hydraulic hoses endure tough operating conditions which eventually take their toll. If not inspected on a regular basis, abrasion, heat, age, hardening, pressure and other factors can cause a hose assembly to burst and leak. However, many hose failure problems can be addressed by making sure the hoses are compatible with the environment in which they will be operating. Problems can be reduced through careful routing and assembly procedures, however, the majority of hydraulic hose failures can be avoided through effective inspection and routine maintenance.
If you need any assistance, contact our helpful on-site maintenance staff. Berendsen’s fleet of mobile maintenance vehicles is armed with specialist hose-fitting equipment and is on hand to diagnose and fix many common hydraulic maintenance issues.