There are applications that combine working conditions of pressure, temperature, flexing, aging and mechanical loads the designers could never have thought of.
Think of hydraulic hammers as they pound into rocks, tree harvesting machines as they lift and tilt huge tree trunks, ground engaging tools on backhoes suddenly hitting a rock or root hydrostatic transmissions suddenly being thrown into reverse gear while travelling forward.
All these applications and many more put great stresses on hydraulic hose assemblies.
It’s not possible to design laboratory tests to simulate all the possible combinations of conditions that a hose coupling may encounter during its life, there are some extremely demanding tests that are used to test hose assemblies and couplings before they are signed off to go into production.
The evidence gathered over many years shows that if hose assemblies can pass these rigorous tests in the research and development lab, they will perform trouble free for years in their final application.
Two basic static tests
There are some basic static tests that can be undertaken:
1. Burst testing
A simple burst test will show if the hose assembly meets minimum burst pressure.
2. Tensile testing
This is trying to pull the coupling out of the hose mechanically. This is an indication of how well the coupling grips the hose.
These two tests by themselves are not enough to prove the coupling design.
Think of the many pressure changes that occur within a hose over its lifetime, not to mention the temperature changes, bending and flexing, end and side loading.
All of these factors demand the hose to coupling interface be able to withstand the most demanding applications thrown at it.
A dynamic (fatigue) test is required to test the hose assembly to its limits.
Standard Testing Protocols
For this reason, the Society of Automotive Engineers, SAE, long ago developed Specification SAE J343: “Test and Test Procedures for SAE IOOR Series Hydraulic Hose and Hose Assemblies”.
There are also similar, almost identical, tests covered by:
AS (Australian Standards)
EN (European Norman)
DIN (Deutsche Industrie Normen)
ISO (International Standards Organisation)
These impulse tests subject the hose assembly to a specified number of impulses (very sharp and quick pressure peaks), at 100% to 133% of the hose’s maximum working pressure, at maximum working temperature, while being bent to minimum bend radius in either a 900 or 1800 arc (depending on bore size).
The combined factors of the extremely rapid pressure rise and release, high temperature, and tight bends, over a large number of pressure impulse cycles soon sorts out the good designs from the bad.
These conditions are tightly controlled, to ensure that the hose assembly is subjected to appropriate stresses before being approved.