If someone were to drop a post-war rail engineer into a 21st century depot, I’m sure he’d feel fairly at home. On the face of it, much of the equipment looks very
familiar, but when you dig a little deeper, that is where the similarities end.
The last 50 years have seen a quiet revolution in the maintenance of rolling stock. Gone are the simple, labour-intensive regimes in which components could be separated into small packages. We are now in an era where strength and precision are crucial, as train builders create large-under floor modules for ease of manufacture and removal.
Complex train control systems and improved passenger facilities mean that decoupling takes time, so unscheduled maintenance involving full under-floor access can potentially delay a train’s availability and disrupt services. In some cases this can result in a penalty for the operator for non-availability of rolling stock.
As a result, manufacturers of depot equipment are finding ways to lift increasingly longer trains. The industry is even talking about ‘formula one style pit stop’ facilities for rolling stock that would see a bogie changed within two hours. So how do we meet these quick turnaround times, without compromising safety standards? We believe it is to make just as rapid technological advancements to enhance the capacity of our equipment.
Jack control systems are a key area in which technological gains are driving forward innovation. The latest networking expertise is being employed to synchronise larger numbers of jacks, whilst still producing a smooth and safe lift. By broadcasting the theoretical position of every jack in a chain at regular intervals, each unit can monitor its position against this information. If the measured height deviates by more than the permitted tolerance, speed adjustments so precise they are undetectable to the eye take place to correct the difference.
As the number of operatives required to lift rolling stock reduces, the quality and quantity of information we can provide has increased commensurately. A chain of jacks can now be operated remotely from a full colour touch screen control panel that displays useful information about maintenance, servicing and faults in a similar way to a car dashboard. The user can monitor an entire lift from one screen, or focus in on a particular jack, should a problem arise. These improvements in data collection and communication mean diagnosing a fault is much quicker and obstructions can be identified without having to check each jack manually.
Time and power savings are being found, as technology enables old, cumbersome maintenance procedures to be streamlined. The use of inverters to control the drive system has also seen great improvement in power usage. As the inverter regulates power to the motor much more efficiently, loadings drop dramatically.
Whilst these general objectives are common to all maintenance depots, the specific apparatus needed in any one location depends on fleet size, frequency of routine component replacement, estimated unscheduled work and availability of spare rolling stock to maintain service commitments. Engineering equipment, therefore, falls into two main functional categories: general maintenance and heavy overhaul.General maintenance equipment
This is normally required to carry out on-train maintenance, such as wheel turning, plus the removal and replacement of items that need to be returned periodically to the manufacturer during their useful life.
Lifting jacks, which I have already touched upon, are at the core of general maintenance and offer complete flexibility in terms of rolling stock type, configuration and location. They are vital for access to bogies, wheelsets and under-floor components and can be linked together to lift long trains without placing stress on the body shells or couplers. It is now possible for a set of 48 jacks to be used simultaneously for a 12-car lift or configured into sets of four or more.
Under-floor lifting systems are considerably more expensive than jacks, but offer certain advantages, namely speed and convenience of operation, plus they eliminate the need for inspection pits. They are best suited to new build depots designed for one train type, or ‘captive stock,’ as the vehicles are lifted by an in-floor system that raises the rail sections under the bogies, then deploys retractable stands to support the body while one or more bogies are removed. Depending on the system, the bogies are transported sideways via turntables, or rolled out along the track beneath the raised vehicle.
Fixed location bogie and wheelset drops are another way to remove under-floor modules without lifting or splitting the train, permitting regular inspection and cleaning to be carried out simultaneously. This makes them particularly beneficial when an unscheduled change is required within a regular servicing timeframe. Drop systems involve initial investment in pit construction, but can provide a complete and very flexible maintenance solution, incorporating a through pit to allow access along the entire road if necessary. The smaller wheelset drop is useful for unscheduled removal when other lifting equipment is otherwise engaged.
Components grouped together in underfloor modules weigh several tonnes and need accurate handling to avoid damage or injury. Basic scissor tables are now being superseded by handlers that facilitate fine adjustment in various axes and may feature optional jigs or fixtures compatible with specific modules.
Battery-powered component handlers are becoming a favoured alternative to a trailing power cable and for safe handling of smaller modules, special undercar manipulators with optional quick change adaptors help overcome manoeuvrability and accessibility problems.
In depots where rails are elevated relative to the floor, rail removal systems enable sections to be taken away to give clear access to the underside of a carriage. Depending on the depot layout, this section may be rolled out or swung clear like a gate, allowing wheelsets or modules to be removed for overhaul. A number of removable sections can permit multiple working locations and shared use of facilities whilst given sufficient rail elevation and other design requirements, this system may also be adapted for bogie removal.
Appropriate access equipment is often built into a depot (in the pit or at high level) to provide safe and efficient access to various parts of the rail vehicle. Fixed equipment does not always offer the required degree of flexibility, so it is supplemented with standard battery-powered scissor platforms. When access is required beyond the wheelbase of the platform, safety considerations dictate that guided or counterweighted equipment must be employed. Thanks to recent innovations, access platforms with automated height adjustment are now able to interlock with other equipment to ensure overhead line clearance and full safety gate functionality. They can also be designed to cover the full length of a coupled train.
The latest laser measuring systems are a must for checking wheel, brake disc and rail wear, whilst sandbox refilling systems should not be forgotten. Shunters may also be needed to aid the movement of vehicles within a depot.Heavy overhaul equipment
The heavy overhaul work carried out at some depots can include stripping down and rebuilding bogies and even the refurbishment of vehicle bodies and interiors. Bogie and wheelset turntables enable items that have been removed from rolling stock to be moved between adjacent roads and around the depot as necessary. Turntables may be electrically or manually rotated and if bogies are to be subject to high pressure cleaning, resistance to water and chemicals, as well as dirt and debris, are key requirements.
Lifters and rotators are also used to handle bogies, but may be designed to facilitate inspection and overhaul of other components as well. Lifters can incorporate two or more jacks with adaptors to engage a bogie frame, offering low-cost flexibility, or they may take the form of in-floor equipment that raises a bogie on its wheels, which is quicker and easier to use and provides a clear floor when lowered. Bogie and module raft rotators may be fixed or mobile. They are equipped with adaptors to fit and grip the component, enabling overhaul access at any required angle.
Once wheelsets and bogies have been reassembled, the suspension must be set on a bogie test machine. Known as a bogie press, varying load cycles are applied to simulate accurate use, which are monitored for load and ride height.
Keeping large items at overhaul facilities can present space and accessibility problems. Stacking frame and pallet systems are used to store traction motors, module packages, wheelsets and bogies, which can then be moved by crane or forklift. For better floor space and efficiency, automated crane and grab equipment may be incorporated into a custom storage solution.Conclusion
Pressure to increase rolling stock availability by reducing maintenance times means the development and refinement of depot equipment will continue. The need to service coupled vehicles, combined with the safe and accurate handling of heavy equipment modules, is making it increasingly important to integrate all required equipment into new depots at the design stages. Installation later is possible, but sometimes more costly.
Richard Carr is managing director of Mechan Ltd