Caterpillar recommends cleaning a hydraulic hose by using compressed air to push a foam projectile through each end of the hose.
Weeping hoses are a sure sign of impending failure.
Abrasion is the primary cause of hose failure.
Routine inspection allows you to catch many hose issues before they become failures.
The proper connector tightened to the appropriate torque value helps prevent leaks.
New technology, such as this LifeSense hose from Eaton, will notify users when it is time to change the hose.
Hydraulic hoses are literally the life lines of most construction equipment. Nothing can grind productivity to a halt faster than a ruptured hose. A little time invested up front to monitor the condition of the hydraulic hoses and fittings can dramatically reduce expensive failures in the field.
“The potential cost of hose failure in terms of lost production, environmental impacts and possible injury to operators and others argues strongly in favor of replacing hoses on a time-based schedule, periodic visual inspection or some combination of the two,” says Douglas Jahnke, marketing manager, Eaton’s Hydraulics Group. “Hose replacement while equipment is already ‘out of service’ as part of a planned preventive maintenance schedule can prevent critical downtime and expense.”
“As a general rule, hoses should be replaced as part of a preventive maintenance (PM) program, especially in critical applications,” agrees Tim Deans, Gates Global Hydraulic Systems engineer. “Consider that hose shelf life is similar to automobile tires. After four to six years, the rubber begins to break down and you can expect to see visual cracking and weeping around the couplings.”
Monitor for Signs of Failure
A preventive maintenance program for hydraulic hoses and fittings should begin with a thorough inspection.
“If there are no signs of leaking, abrasion wear, cracks or twisting, then there is no reason to proactively replace the hose assembly,” says Ronald Gruber, Caterpillar. “However, other considerations — including the remoteness of the jobsite or cost of the machine being down — may prompt some customers to replace hose assemblies at a scheduled overhaul, especially if the customer has developed experience with hose life in specific applications.”
A visual inspection can catch many potential hose failures. “In many (but not all) cases, there are indications of an impending failure,” says Gruber. “Wetness or leaks, cracked rubber, loss of flexibility or worn rubber are all signs of a potential problem. There is really no reliable way to tell how long a hose assembly will last once these symptoms are noticed.”
Joseph Skovrinski, Gates Condition Monitoring Engineer, agrees, noting, “In most cases, hydraulic hoses will provide clues that indicate a pending failure. That’s why it’s important to conduct a daily visual inspection before operating hydraulic equipment. But never conduct an inspection by running your hand over the hose while the system is pressurized. Hot materials and chemicals can cause serious bodily harm, or even death.”
No hose assembly will last forever. “All hydraulic hose assemblies ultimately will fail and they often generate consistent indicators of impending failure,” says Jahnke. “Until recently, however, there has been no practical way to detect those indicators and proactively replace the hose. The good news is that the technology now exists to monitor those indicators and provide a warning of impeding failure.”
For example, Eaton LifeSense hose delivers this capability. “As the technology becomes more widespread, the need to throw away perfectly good hose on a time-based schedule will disappear,” says Jahnke.
Gates also offers advanced hose monitoring technology. “For highly critical applications, it pays to install a hose monitoring and diagnostic system, such as Gates Sentry IQ,” says Skovrinski. It monitors what goes on inside a working hydraulic hose. “It measures pressure spikes and correlates them to the temperature inside the hose when the spike occurs. This correlation between the temperature and the pressure estimates the end-of-life for hydraulic hose assemblies.”
While many types of hose may look similar and even have the same physical dimensions, there are key differences you must understand. “The important thing to remember is the replacement hose must meet or exceed the specifications of the old or original hose assembly,” says Gruber.
Choosing the correct hose has a major impact on downtime. “Equipment operators and technicians can reduce, if not eliminate, premature hydraulic hose failure by giving maximum consideration to hose assembly selection and installation,” says Deans. “Yet, with all of the different types of hoses on the market, choosing the right one can be difficult. Gates suggests using the ‘STAMPED’ method to ensure you get the right hose assembly for the job. STAMPED stands for Size, Temperature, Application, Material to be conveyed, Pressure, Ends or couplings, and Delivery.”
Be wary of adapters that let you use a different size hose. “Adapters allow field operators to change OEM hose with a different size or type that may not be appropriate for the OEM equipment,” Deans cautions. “For example, to save money, or because a parts store doesn’t have the exact replacement hose in stock, an operator may replace a -12 hose (3/4-in. ID) with a -8 hose (1/2-in. ID), using an adapter to drop down a size.” This can have negative results. “Using the smaller size could increase the fluid velocity inside the hose, generating heat, crimping the hose, or exerting excess pressure on the coupling — all of which could lead to premature hose failure.”
Many users can be tempted to use adapters due to lack of hose availability. “The biggest offender is -10 hose (5/8-in. ID), which is not prevalent in North America,” says Deans. “Operators typically want to drop down to a -8 (1/2-in. hose ID) to save money. On a drive or control mechanism, doing so could cause the equipment to behave unpredictably.”
Also keep track of any trouble spots on the machine. “One often overlooked factor in hose replacement is frequency of failure at a particular location on the equipment,” notes Jahnke. “If a particular hose fails or requires replacement more often than average for all of the hose on that piece of equipment, it may be prudent to upgrade to a stronger or more durable product.”
He adds, “It is particularly important to follow proper installation procedures, as well as guidelines regarding minimum bend radius, twist and orientation, securement and storage. Most hose will carry either a generic SAE or ISO specification on the ‘Layline’ or a manufacturer’s product designation. For example, a SAE EN856 Type R12 is a four-spiral high-pressure hose specification, which prescribes certain levels of performance no matter who manufactures it.”
All manufacturers provide cross references between generic designations and their proprietary product numbers. “However, in some cases, a manufacturer will exceed the specification, providing even higher levels of service and longer life,” says Jahnke.
Keep the system clean
Today’s high-performance hydraulic systems utilize extremely tight tolerances that can easily be damaged by even small amounts of contamination.
“Before removing hose from equipment, spray it down with brake cleaner to remove all the oil, grease and debris,” says Deans. “This will minimize the chance of dust, dirt or grime falling into the port when you remove the hose. Use a cap or plug to close the ports on the machine while you are servicing the hose or waiting for a replacement to prevent dust or debris from being blown into the ports. If you have a replacement hose on hand, you can forego capping the ports and simply install the new hose. Use brake cleaner to clean the threads and surfaces that the replacement hose will mate to in order to avoid introducing contaminants into the hydraulic system.”
Gruber advises, “When a broken hose assembly is removed, the preferred method to keep contamination from entering the system is to install clean plastic or metal plugs and caps to cover all open hose ends, tube ends and related ports. Wrapping exposed hose ends, tube ends or related ports with clean plastic is also acceptable.”
Don’t leave anything exposed longer than absolutely necessary. “Any system port exposed to the atmosphere is a potential entry point for contaminants, so the duration of that exposure should be as short as possible,” says Jahnke.
New doesn’t mean the same as clean. In some instances, the new hose can have debris left over from the manufacturing process. “It is very important to clean new hose assemblies prior to installation,” notes Gruber. “An unclean hose assembly is an easy way to introduce contamination into the hydraulic system.”
To remove contaminants from a new hose assembly, Caterpillar recommends shooting a foam projectile through the hose and couplings using forced air. “This procedure is done twice, once in each direction though the hose assembly,” says Gruber. “After cleaning a hose assembly in this manner, the ends should be capped and plugged to further protect the assemblies from contaminants during transport and storage.”
There are other ways to clean a hose, as well. “Cleaning methods vary based on shop capabilities, the cleanliness level required and the critical nature of the application,” says Skovrinski. “For hose going to a pumping component, cleanliness is absolutely critical; for hose going to a tank or filter, cleanliness is less critical.”
Three different methods are used to clean hydraulic hose assemblies with varying levels of cleanliness: shop air blow, pellet gun (projectile or ‘cleaning pig’) or fluid flush. “The easiest and most commonly used cleaning method is to blow shop air through the hose assembly after the hose has been rough cut to the desired length,” says Skovrinski. “However, a shop air blow offers minimal cleaning and is the least effective method.”
A better method is to use a pellet, which is shot through the hose with compressed air. “The pellet breaks up the debris and cuttings that accumulate up to 6 in. back from the hose openings after the hose has been cut, and flushes them out of the hose,” says Skovrinski.
“A fluid flushing apparatus provides the most effective cleaning method,” reports Skovrinski. “With this technique, cleaning fluid is flushed at a high velocity through the hose until the hose meets the strictest cleanliness levels. After cleaning, cap the assembly on both ends to prevent debris from entering until the hose is installed.”
Through daily inspections, a proactive preventive maintenance program, proper selection and a concerted effort to maintain cleanliness, you can eliminate much of the downtime due to hydraulic hose failure.