Even in optimal conditions, and in cases where hydraulic hose assemblies were properly made, the life expectancy of any hydraulic hose assembly is directly related to the operating parameters of your application. When a hose fails, it is often the result of some form of human error, misapplication, improper usage, or improper maintenance.
So, let’s look at the most common incidents that go wrong with hoses, the likely causes, and how to address each of these situations. Knowing how to properly identify any of the key causes of failure will help you avoid emergencies in the future!
A bursting hose occurs when the wire reinforcements fail in the braid along the outside of the hose. When this happens, there is little to no outward deflection of wire in the failed area. This can happen when a hose has simply lived out its service life, but it can also be a result of a high number of pressure cycles, or a continuous flexing of the hose in that one area. If you experience a burst hose, we recommend that you review the application, replace the assembly, and develop a preventative maintenance schedule.
Sometimes a hose will burst at the fitting, and there will be broken wires at the last shell grip or sometimes at the end of the nipple. This occurs when the hose continuously moves or pulls at the fitting. Excessive movement may be the result of pressure surges, the hose assembly length being too short, incorrect crimp dimension, or the hose bend may begin too close to the fitting. This can be fixed by lengthening or re-routing the assembly to allow for some slack. It is important to never stretch to fit, as assemblies may shorten when pressurized. Before starting to bend it, the hose should be routed straight for at least double the inside diameter of the hose. Clamp the assembly as necessary to avoid movement and review crimping techniques as well as proper tooling.
When a hose bursts at an outside bend, it stays set in a bent position, usually in sort of an oval shape—yet it’s still flexible. There may be some broken wires near the problem spot on the outside bend of a hose. If the application is a vacuum or suction, the hose may tend to be flattened out in the bend area, which may restrict the flow. If the bend is severe enough, the hose may have a kink. This happens when you don’t use the recommended minimum bend radius or the starting bend right at the fitting. When this occurs, the hose assembly has to be replaced. When doing so, you should make sure to re-route the new hose assembly to increase the bend radius according to the requirement. The hose should not begin to bend for a minimum distance of two times the inside diameter of the hose, and then stay within minimum bend requirements. It is also important to use the proper clamps as required.
Sometimes pressure issues cause a hose to burst in multiple places. These are usually clean bursts with no random wire breakage and no sign of wire-on-wire abrasion or cover abrasion. This is normally caused by excessive pressure or pressure in the range of the minimum burst rating for the hose. You can adjust the system pressure to be within the established working pressure of the hose or replace the hose with one that has a higher working pressure than the system pressure. Don't forget to include any pressure spikes when choosing the PSI of your hose.
A fitting can blow off when the hose is not inserted into the shell of the fitting per the recommended length—which means all the grips are not being used. All the grips in the shell are needed to hold the fitting onto the hose. In fact, the last grip in the shell does about a quarter of the work in holding the fitting to the hose. In this case, you simply have to replace the hose assembly, and before inserting the fitting, make sure you mark the cover of the hose per the recommended value stated in our catalog—then insert the fitting until the end of the shell lines up to your mark.
When the assembly leaks between the shell of the fitting and the hose, it causes the fitting to blow off as well. This can happen when the shell of the fitting is either under or over the recommended crimp specifications. In this case, the hose assembly needs to be replaced and checked for proper fitting usage. It is also important to review the crimping instructions for the particular crimper being used, including tooling.
External damage to the hose cover occurs when the hose bursts around an area where there is an obvious twist in the hose. You will be able to see some broken wires. This occurs when the hose gets an unwanted twist during the assembly of the fitting due to a lack of proper lubrication. The next step is to review proper hose assembly procedures and replace the hose assembly. You may also have to use clamps to re-route the hose using the hose layline as a guide to assure the hose flexes in one plane.
When the cover has foreign object damage and/or abrasion, the reinforcement wire shows signs of being rubbed and possibly torn and corroded. This is from excessive rubbing or chafing of the hose against an external object—possibly other hoses or the wrong size clamp, or perhaps the impact of the hose on sharp corners or brackets. This could potentially call for: replacing the hose assembly, use a protective sleeve or hose guards, re-routing the hose assembly or, if appropriate, use proper-sized clamps to avoid contact with other objects.
When the hose bore appears to be torn or may have broken loose from the reinforcement and piled up at the end of the assembly, resulting in a reduced flow or maybe no flow at all. In these cases, the outside of the hose may show signs of being flattened. This comes down to vacuum failure; the hose may have been kinked, flattened, or bent too sharply. In some cases, it may be due to poor adhesion or insufficient cure of the inner tube. Replace with a hose rated for the specific vacuum application.
When hoses are exposed to temperatures below their recommended limits during hose movement, the hose becomes affected. To address this issue, review the application and raise the temperature to within the boundaries specifies or replace it with a hose recommended for the given temperature parameters.
Heat effects can be apparent when the hose is hard, brittle, and cracks when flexed at room temperature. On its cover, there may be visible signs of being dried out and charred. What’s happened is aerated oils have caused oxidation in the hose’s inner tube, making the hose harden. Any combination of oxygen and heat will accelerate the hardening of the inner tube. The same effect may be caused by cavitation—the formation of empty spaces within the material; long service life can create these symptoms.
If your hose isn’t near or beyond its service life -
review the application
lower the temperature to within the hose’s working limits
replace the hose with one that has a qualified temperature rating
install heat guards or shields as required
If you find a hose’s inner tube contains numerous fine cracks yet remains flexible, and no cracks are found in the hose under the fittings, then the internal air may be too dry—probably due to the use of a lube-dry compressor or a refrigerated air-drying system. Replace this hose assembly with one that is rated for extreme dry air.
When fluid is emitted at high velocity from an orifice and hits the inner tube, erosion occurs, and eventually, the inner tube is gouged through to the wire braid for several inches, causing the hose to spring a big leak. The erosion can also be caused by particles in the fluid. When this happens, you must replace the hose assembly.
Fluid can be incompatible with just the inner tube, which can
In this situation, you need to replace the hose assembly with a hose that’s compatible with the fluid to be used or replace the fluid with one that is compatible with the hose material.
When a hose cover blisters, these blisters might contain fluid or a grease-like substance which may be a combination of the system's fluid and the plasticizers from the hose material. This happens when there’s fluid incompatibility with the hose materials. If this is the case, you should replace the hose assembly with one that’s compatible with the fluid, or replace the fluid with one that is compatible with the hose.
Check out our STAMP blog series and videos for additional information on selecting the right hose for your specific application.
If you have any questions about assembly techniques or bending, talk to your local ParkerStore professional or read our hose installation and routing blog for best practices. Also, talk to your ParkerStore pro about ways you can extend the life of the hydraulic hose in your application.
Knowing the above will help you in understanding how hose failures are caused, how to address them, or better yet, avoid them altogether. It is crucial to ensure you have the correct hose assembly and that it’s set up properly. Remember, you can always turn to the pros at your local ParkerStore—they will make sure you have the product that’s right for your application, and answer any questions you might have.
Watch the video and see Mike, our ParkerStore professional, walk-through the key reasons a hydraulic hose fails:
Article contributed by:
the ParkerStore Team, Parker Hannifin
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