In hydraulic systems, hoses carry pressurized hydraulic fluid to or from pumps, motors, valves, actuators and other system components. Due to their critical function, the hoses employed are designed and constructed for suitable flexibility and durability. They must be flexible enough to bend in and around the confines of equipment, fit into tight spaces and may span long distances while being durable enough to withstand the high operating pressures and temperatures. For these reasons, they are generally made from a combination of multiple layers of materials—such as elastomers, fluoropolymers, thermoplastics, textiles and metals. Typically, hydraulic hoses have an inner lining or tube made of rubber or thermoplastic, braided or spirally applied reinforcement layers of textile yarn or wire and a cover also made of rubber, thermoplastic or braided material. All of these are uniformly bonded together as one unit. Finally, for a hydraulic hose to be useful it requires suitable connections with hose fittings (permanent or reusable type) designed to attach to the hose to allow full utilization of the hose’s rated pressure and performance for maximum service life. It is vital to achieving this maximum acceptable service life and safe use that only manufacturers matched and approved components must used together and assembled to their recommendations. Mixing/matching of hose components outside of this recommendation can lead to unsatisfactory performance and disaster.
While hydraulic hoses are highly durable, the pressure cycles they experience through normal operation and natural degradation will eventually lead to failure. If hose failure occurs unexpectedly, it can result in employee injury, property damage, expensive cleanup, wasted production, unscheduled downtime and increased material and labor costs. With these consequences in mind, most hose experts recommend a proactive rather than reactive approach to hose replacement—i.e., replacing the hose assembly once it nears the end of its safe and useful life span but before it fails—for the sake of safety and cost savings.
Given the durability generally demonstrated by modern hydraulic hoses, it can be challenging to know when it’s time to replace them. Sometimes there are obvious signs that a hose has begun to fail, but that’s not always the case. In the following article, we discuss when and how to replace hydraulic hoses.
What Is the Typical Service Life of a Hydraulic Hose?
The Society of Automotive Engineers (SAE) has generally set the standard shelf life of unused bulk rubber hoses to ten years from their date of manufacture when properly stored. However, there are many factors that influence the actual working or service life of a hydraulic hose, such as the type and temperature of the fluids, operating pressure and flow, static or dynamic conditions and environmental conditions. While the hose manufacturer or distributor can provide insight into the expected working life when in doubt, replacement should not be delayed if the hose is showing any signs of wear or degradation. Most hydraulic hoses are designed to pass the cyclical impulse pressure requirements at specific pressure levels above the rated working pressure, temperature and bend radius. This qualification testing requires the use and assembly with the properly specified end fittings attached to the hose for a number of cycles. For example, most two wire braid hoses require a successful testing of a minimum of 200,000 pressure impulse cycles, while most wire spiral hoses require at least 500,000 cycles. This is why wire spiral hoses are normally considered longer service life hoses for equipment running lots of pressure surges within the hydraulic system.
You must keep in mind that every application is different and no manufacturer can predict with accuracy a service life for a particular situation without in depth knowledge of all parameters. The equipment designer bears this responsibility for a given system.
Generally, if the service life of a hose has proven to provide acceptable durability, replacement with the same or better rated hose should also provide similar life. The branding on the hose can usually provide the rating such as the manufacturer’s part number and/or the SAE or ISO ratings.
Factors Influencing the Service Life of Hydraulic Hoses
As indicated above, the actual working life of a hydraulic hose depends on many factors. Some of the considerations to keep in mind when assessing how long a hose assembly may provide acceptable service life include:
- Size: Hydraulic hoses differ in size depending on the anticipated flowrate needs of a system. It’s important to be aware of the limitations of the hoses employed to avoid exceeding their operating capacities. Excessive velocity will damage the inner surfaces of the hose’s tube and other system components may be damaged from the tube debris. Excessive flowrate will also raise the temperature of the hydraulic fluid due to friction. Using a simple nomograph provided by the hose manufacturer provides guidance in safely sizing the hoses for hydraulic system’s pressure and return circuits once the pump output flowrate is selected. Normally, return hoses must be sized larger than pressure lines (see manufacturer’s nomograph).
- Temperature: Typical rubber hoses are designed for operating temperatures ranging from -40° F to 212° F. Certain other hose materials can provide safe performance up to 250°, even 300° F. PTFE tubed hoses can safely be used up to 450° F. Hydraulic fluids or ambient conditions outside of this range can lead to premature failure. Higher temperatures can lead to the hose becoming hard, brittle and cracked, while lower temperatures result in the hose becoming cracked without losing its softness or flexibility. The cooler the hose fluids can be usefully used at well below the rated maximum, the longer the hose will be able to not experience material degradation. Care must be taken to properly route and shield hoses away from external heat sources such as engine manifolds which can quickly reduce the life of the hose and often lead to fires.
- Pressure: In addition to having set operating temperatures ranges, hydraulic hose assemblies have maximum rated working pressures. If the system pressure exceeds beyond this point, the hose may suffer permanent damage and/or fail. For this reason, it is recommended to use hoses rated for a few hundred psi over the system’s maximum working pressure to avoid surpassing the hose’s rating. The integration of quick acting pressure-relief valves can also help minimize the risk of excessive pressure spikes. Pressure spikes create cumulative damage within the hose and adds up over time and eventual likelihood of hose failure.
- Application: Each hose is designated for a specific set of system functions and duty cycles. However, even when used properly, hoses can be damaged by environmental factors related to their application. For example:
- Hoses used in mobile equipment often rub against other equipment components or even other hoses, which leads to damage to the cover and reinforcement over time. Again, routing of hoses near engine exhaust components can quickly damage a hose from the high temperatures.
- Hoses used in indoor environments may be exposed to higher temperatures, especially when situated near furnaces or ovens, which can lead to thermal damage.
- Hoses used in vertical installations experience more stress than those used in horizontal installations.
- Hoses used in applications with cyclical pressure loading can move due to up to 3% change in length. Hoses have to be routed and design length chosen to account for this movement. Any such application should have suitable inspection of the hose to see if there is degradation of the hose itself or the connections leaking. Any rotation of the fitting swivel under use will lead to leakage or ultimate failure unless the connection is made using a “live swivel” intended for dynamic swiveling.
- If the hose is installed on components that experience movement (such as a pivoting hydraulic cylinder) routing is very important to allow for proper length for flexing and all twisting or bending in multiple planes of the hose should be avoided.
While these conditions may be unavoidable, ensuring the hose is properly installed and implementing protective measures (e.g., hose guards or shielding) can significantly extend the service life of the hose assembly.
- Fluid: When selecting a hydraulic hose assembly for a system, ensure all of its construction materials are compatible with the chosen hydraulic system fluid. Its compatibility can be determined by checking the Material Safety Data Sheet (MSDS) for the fluid in combination with the hose manufacturers listings of compatibility. Using incompatible materials can damage the assembly and compromise system performance. Some fluids can easily damage the hose tube and lead to failure, so you must make sure of compatibility with the hose.
Signs Signaling a Need for Hydraulic Hose Replacement
While it is often difficult to determine whether a hose assembly needs replacement, there are some visual cues that indicate it has reached the end of its service life. For example, if the hose assembly has any of the following conditions, it must be replaced:
- Crushed or distorted hoses
- Fluid leakage (within the hose length or at the fitting end)
- Exposed wire reinforcement
- Significant surface damage (beyond scuffs and small nicks)
- Kinks (an indication of incorrect routing)
- Twisted hoses (another indication of incorrect routing)
- Hardened or blistered cover as well as any signs of the cover softening significantly which may signal a fluid compatibility problem
- Corroded fittings (white oxidation is normally, acceptable while red rust warrants replacement)
Steps for Replacing Hydraulic Hoses
The replacement process for a hydraulic hose is as follows:
- Identify the issue. Verify which hose is damaged before removing and replacing it. Be thorough in assessing the situation to ensure that the repair actually addresses the problem. With this information in hand, purchase a suitable replacement that will provide same or better performance rating.
- Assess the situation. Check what system components need to be removed to allow for the replacement of the problem hose.
- Prepare the system. Address any components connected to and around the hose to ensure they do not hinder the replacement process. This step must include relieving pressure to avoid the leakage of process fluids, lowering pieces to the ground to prevent them from falling and removing parts to allow for an obstructed view and workspace. Note, at this point it may be useful to photograph a few suitable views of the hose’s routing to assure a replacement is put back in place properly.
- Loosen the fittings. Once the hydraulic assembly is prepared for the actual replacement operation, loosen the fittings as required that attach the hose to the machine.
- Remove the hose. When the fittings are loosened, remove the hose and pour any residual fluid into a waste container.
- Seal the fittings. Before installing the replacement, seal the fittings with a designated fitting plug or rag to avoid further leakage.
- Install the new hose. Install the replacement using the proper techniques and reassemble the rest of the system. Refer to manufacturer’s recommendations for details and any applicable torque recommendations. Consider tagging the hose (see later in this document).
- Visually check the installed hose. This will help make sure the installation is proper in routing and connection.
- Test the system. Once the hose assembly is replaced and the system is fully reassembled, test the system to ensure there are no leaks or performance issues.
Determine Replacement Intervals
Keep records as to what the inspection of the hoses is showing regarding hose durability and determine what replacement intervals may be needed to assure hoses are replaced before failure. Tagging the hose when installed, inspection intervals and replacement dates will help in this process. The goal is to make sure that the hoses are replaced before failure.
Contact the Hydraulic Hose Experts at Jason Industrial Today
All hydraulic hoses will eventually fail. Preventing their failure from affecting equipment or facility operations necessitates proactive measures, as outlined above. For further assistance determining when and how to replace a hydraulic hose assembly, turn to the experts at Jason Industrial.
At Jason Industrial, we have over six decades of experience handling industrial hoses and an extensive selection of hydraulic hose products. These qualities make us the ideal partner for all hydraulic hose needs. To learn more about our offerings and how we can help extend the service life of hydraulic equipment, contact us or request a quote today.