Often taken for granted, hoses are a vital part of the hydraulic system. However, when neglected, their failure can have severe consequences for machinery, the environment and for the well-being of those who must work around them.
The National Fluid Power Centre (NFPC) has been running a series of ‘Ask the Experts’ webinars to raise awareness of the importance of implementing an effective hose management scheme and the benefits this can deliver.
“Hoses may be a lower-cost item and often taken for granted,” states John Savage, NFPC director, “but failure may endanger life, and cause damage to machinery and the environment at a very high cost. It’s vital that those who are using the technology have been properly educated and trained to handle the equipment, as should anyone working on and maintaining hydraulic systems.” Everyone should be trained at a level that meets or exceeds the minimum educational recommendations of the BFPA (British Fluid Power Association), he states.
What is the worst-case scenario where a hose management scheme hasn’t been put in place or staff have not been effectively trained? Savage replies: “You might have a situation where a hose has been damaged while connected on site, and an operative decides to go in and replace it without taking the proper precautions, such as isolating the equipment, locking it off and applying proper safe working procedures. It must be remembered that this active machine will have been installed with hoses that meet a particular specification, and replacement hoses must meet the same specification and be correctly installed by fully-trained competent staff as part of the hose management scheme.
”While a great deal of attention is paid to the functioning and maintenance of the major hydraulic components – pumps, motors, valves, for example – unfortunately how the actual oil is transported from one part of the system to another to carry out the task in hand is often given less consideration,” he adds.
CONTEXT IS ALL
Philip Ingate, training manager for Parker Sales UK & Ireland, stresses the importance of the application in considering hoses. He says: “Our products have to work across every industry, for every type of application, and right across the world. We manufacture and design a vast range of hydraulic hoses to meet that need, so any given hose has to be selected to perform the task required, then assembled correctly and finally given to the user for installation. If any one of those elements were not to be managed correctly, in accordance with the ‘STAMPED’ guidelines [see box], it could cause a damaging domino effect, so it is essential to manage that process at every stage and throughout the life of the hose.”
By way of example, Ingate points to the extreme consequences that a hose failure can provoke. “If a £500 hose on a £5 million tunnel boring machine were to fail suddenly, the machine would grind to a halt, possibly causing serious delays, as well as financially impacting the project. So you must have a high-level inspection system in place, covering maintenance, inspection and the timely scheduling of hose replacement, so they can be swapped out before failure occurs.”
He also emphasises how no single strategy can be applied to hoses collectively, as the environments in which they function can be so varied. “There is no one measurement or standard that can be applied when you are working with differing pressures, flows, media and exposure to UV and ozone, for example. So, that is where the criticality of the inspection system comes in. Some hoses under extreme conditions will need frequent checking, whereas for others in more benign environments, perhaps carrying only water and operating indoors, it might be every two years.”
One way for users to proactively manage the hydraulic hose inspection and maintenance process is via the web-based Parker Tracking System (PTS). With two platforms to manage their assets, PTS Mobile App and PTS Web App, distributors and end users can retrieve all of the product information and history relating to every single hose in use, via a bar code labelling and scanning system (pictured, top), and schedule a service.
As Savage points out: “Monitoring, logging and tracking the working life history of hoses, from the day they are installed to when they are replaced, has been greatly aided by today’s wealth of technology – mobile phones, tablets, the cloud, barcodes on hoses etc – making hose management far easier to implement. But what lies at the heart of any strategy is that education and training on all aspects of hose management is an absolute must.”
BOX: Hydraulic hose management problems ‘STAMPED’ out
When implementing a hose management scheme, says Richard Walker, an independent consultant and member of the NFPC Advisory & Strategic Planning Group, the acronym ‘STAMPED’ is one that all users of hydraulic flexible hoses need to be aware of and adhere to. “It covers the seven key areas of information that are needed when providing the right hose assembly for any given situation, and it has to be remembered that these can vary greatly from operation application to operation application.”
Each item is worth considering in some detail, he advises, as the success or failure of any hose management scheme is dependent on how well these principles are applied.
Size: The hose inside diameter must be sized to be able to keep the flow velocity within a specified range and avoid damage to the hose due to heat generation or excessive turbulence. Stated minimum bend radius must not be exceeded, as that will lead to hose reinforcement damage. Hose length is also a key factor.
Temperature: Maximum fluid operating temperature and environmental minimum/maximum temperatures should be specified to ensure correct hose materials selection. When routing a hose near a hot manifold, the temperature will accelerate hose ageing and cracks will appear on the hose cover.
Application: This includes correct routing to avoid abrasion of the hose cover that will expose the wire reinforcement, which will then corrode and weaken the pressure resistance, leading to premature failure. It also includes fittings orientation to avoid hose twist that will fatigue the hose when pressure is applied, due to torsional stress.
Media: Some applications require specialised oils to be conveyed through the system. Hose and fittings selection must ensure materials compatibility with the internal media.
Pressure: Working pressures of the hose assembly (including end fittings) must be equal to, or greater than, the maximum system pressure. Frequent pressure surges above the hose rated working pressure can shorten the life of hose assemblies.
Ends: Compatibility of hose fittings with the hose is imperative and this is only possible through integrated design, backed up by extensive testing and accreditation to international standards requirements.
Delivery: In addition to ensuring the hose is sized to prevent excessive flow velocity, it must also be sized to prevent pressure drop, especially for long-length hoses. Charts are available to check pressure drop per metre of hose against the system pump output. Angled end fittings can also add to pressure drop and affect machine performance.