By Josh Cosford, Contributing Editor
Hydraulic hoses are designed to withstand much higher pressure than expected during regular operations, which everyone will agree is good. Should your machine’s working pressure fall within a typical 3,000 psi, you’d be little comforted by a hose designed to burst at 3,100 psi. The slightest pressure spike would lead to catastrophic failure or even personal injury.
We expect hydraulic hoses to handle their everyday demands with ease, which is why burst pressure should be vastly higher than working pressure. Burst pressure is defined as the minimum pressure a hydraulic hose will withstand under specific laboratory conditions before it will fail entirely and permanently. You can expect no less than four times the working pressure before a hydraulic hose fails, providing a significant buffer between typical operation and a bad day.
Using the SAE J343 testing standard, hoses are connected to a test stand and put through their paces to confirm the manufacturer’s design and construction yields no less than four times the rated working pressure. In reality, most hoses exceed the minimum 4:1 burst ratio, which makes sense if you’re a manufacturer. You’d much rather account for any variances in material or construction on any given day at the factory so that even a “bad batch” still meets the requirement.
In the context of the SAE J343 test method for hydraulic hoses, a “burst” refers to the point at which the hose fails under pressure by rupturing or bursting. This failure occurs when the internal pressure within the hose exceeds its maximum capacity, leading to a sudden release of fluid and the physical disintegration of the hose. During burst testing, according to SAE J343, the hydraulic hose is subjected to increasing pressure until it reaches the point of failure. The pressure at which the hose bursts is recorded as the burst pressure or burst strength of the hose.
Part of the J343 standard defines a zone of failure between working pressure and outright failure that should still concern the maintenance team. Under SAE J343, fatigue pressure refers to the pressure at which a hydraulic hose undergoes repeated cycles of pressure fluctuations without experiencing failure due to fatigue. Fatigue pressure testing is conducted to evaluate the durability and resistance of hydraulic hoses to cyclic loading, which simulates the real-world conditions experienced during operation.
According to SAE J343, during fatigue pressure testing, the hydraulic hose is subjected to a specified number of pressure cycles, typically ranging from hundreds to thousands, at a predetermined pressure amplitude. The pressure cycles involve alternating between high and low pressures to simulate the fluctuations that occur during normal hydraulic system operation.
The fatigue pressure represents the maximum pressure that the hose can withstand for a specified number of cycles without exhibiting signs of fatigue failure, such as cracks, delamination, or loss of structural integrity. In the simplest of terms, fatigue pressure should also exceed double that of working pressure. This parameter is crucial for assessing the long-term reliability and service life of hydraulic hoses in applications where they are subjected to repetitive pressure fluctuations.
Using the SAE J343, both hydraulic hose burst and fatigue pressure provide machine designers, technicians and mechanics with important safety information to elicit peace of mind when installing hose assemblies.
Filed Under: Components Oil Coolers, Engineering Basics, Hose & Tubing, Hose Assembly Tips, Technologies
