As the drive to reduce the costs of maintenance and replacement components continues to gather pace, the demands on those who supply critical components become more stringent too. Rail operators and maintenance contractors are increasingly seeking to foster partnerships with companies which can guarantee product quality and availability, and an innovative approach based on deep market understanding which can drive performance improvements and reduce operating costs.
One example of this type of company is Norgren, a global market leader in pneumatic motion and fluid control which has more than 30 years’ experience in delivering a combination of high-performance products, innovation and technical excellence to the rail industry.
As simple as drying air
To understand how a company such as Norgren, which is backed by the global resources and expertise of the IMI group, can offer an ‘engineering advantage’, just consider the supply of compressed air. Moisture and other contaminants make operating compressed air applications very problematic in rail. Air dryer packages are widely utilised to clean and dry compressed air before it reaches critical downstream applications, such as brakes, door systems and pantographs.
Two air dryer types – membrane and desiccant – are currently used. Both have their problems when used in rail applications.
Membrane dryers use fibre tubes suspended between two columns to form a semi-permeable membrane, allowing water vapour to pass through to the low concentration outside.
To maintain lower moisture concentration on the fibre bundle’s exterior surface, much of the dry air produced is employed to sweep away collected water vapour into a small vent which releases it into the atmosphere. This sweeping action is continual so the membrane self-regenerates with no cycling, pressure changes or maintenance.
Membrane dryers are lightweight, have no external power requirement and create no dust. However, the fibres are susceptible to contamination and, if one fibre should break, others tend to follow, causing catastrophic failure.
With a life cycle of up to 24 months, membrane dryers require monitoring and replacement through regular maintenance schedules.
![VR24Z [online]](http://railengineer.uk/wp-content/uploads/VR24Z-online.jpg)
Desiccant dryers, on the other hand, adsorb moisture and contaminants using two canister towers or columns. These are filled with beads combining adsorbent material mixed with a clay binder, which is formed into spheres of various diameters.
Although tightly packed, train vibration causes the beads to rub together, eroding them and forming dust which can then contaminate the air and damage downstream equipment. An additional downstream filter is usually installed to collect dust near the dryer output, but this is not totally effective.
As the beads erode, they become less tightly packed, allowing more moisture-laden air to pass through gaps in the desiccant bed and flow into downstream equipment. Some manufacturers use a spring to compress the canister stopping the gaps between the beads – this can restrict air flow and cause a pressure drop, making the dryer work harder to push air through, reducing efficiency.
As the desiccant bed’s size reduces, it can become over-saturated, with the beads irreparably damaged. Depending on the application, desiccant air dryers have a life cycle between six and 36 months. The frequent replacements mean additional costs, extra maintenance (it is usually a two-person activity, sometimes requiring special lifting equipment) and unnecessary downtime.
There is a better way
Harnessing the best of existing desiccant and filter drying systems, Norgren’s latest generation of air dryers feature Adsorbent Media Tube (AMT) technology which employs a desiccant substance housed within
an extruded polymer tube. During manufacture, the desiccant crystals are mixed with the polymer – although the polymer plays no part in the drying process, its molecules are wider than the clay binding molecules found in a regular desiccant dryer, allowing moist air to get to the drying agent and be adsorbed more quickly. During regeneration, the moisture is removed just as quickly, leading to a reduction in air volume required for the purge cycle.
The polymer tubes are tightly packed into their housing, but are more uniformly shaped than beads, making them unaffected by vibration. This also means consistent air flow through the tubes, while the unit’s performance does not degrade over time. No clay component also means no dust.
AMT polymer tubes are extruded into a water bath during manufacture so they are essentially ‘born’ in water, meaning there will be no by-product or chemical reaction if they become saturated. The tubes are simply dried, returned to their original state and reused as normal, so no maintenance is required.
These new dryers are lightweight but also flexible, being mountable horizontally or vertically. Tests show they collect more moisture per m3 than traditional desiccant or membrane dryers. They also last up to six years or 18,000 hours in most applications, changing their status from regularly serviced items to major refurbishment items. With a considerably lower cost of ownership, they dry better to ensure a reliable flow of clean air to downstream applications, keeping the railway network moving.
And there’s more…
Having dried the air, Norgren also use it. Developed specifically for use with circuit breakers in electric rail vehicles, VR24Z solenoid valves are direct acting, fast response products delivering optimum reliability and safety for a range of applications including cam shaft contactors, line breaker contactors, vacuum and air blast circuit breakers and shoe gear controls. They have recently been specified by a major international rail operator which was experiencing issues with its existing technology.
Norgren’s approach was to modify one of its proven core technologies based on the specific application requirements, and then supply samples to the customer for testing and validation. These products met all specifications over a four-month live train test, resulting in a highly prestigious contract.
A pioneer in door control systems, another of Norgren’s innovations is a reduced force cylinder for external and internal door control. The cylinder has been developed to meet the needs of purchasers who are finding it hard – and often expensive – to source and service OE products. Already, these products have been specified by major train companies and suburban network operators.
So a dedicated rail sector team with good practical experience, such as the one at Norgren, can make a difference by developing and specifying items which are best suited to a railway application. And that’s how you can gain an ‘engineering advantage.’
