Old diesel and electric multiple units were a common sight running in two, three and occasionally four car formations, however these vehicles were easily uncoupled and the jumper cables disconnected allowing single vehicle handling. This fact, together with the multitude of vehicle types, precluded use of anything other than lifting by sets of four railcar jacks or overhead crane.
The introduction of modern coupled vehicles into Britain’s railway system, and the creation of dedicated routes for particular vehicle types have allowed the consideration of alternative lifting methods for maintenance purposes.
One such method is underfloor lifting for both trains and trams, which has for some time been common throughout Europe, where dedicated stock on selected routes is already common practice. This method allows the trains to enter the depot and run on to the underfloor lifts positioned directly below each of the vehicle bogies. With a single press of a button, the entire coupled train is then raised to allow access below for removal of bogies and any equipment modules. Combined body supports are built into some lifters, which support the vehicle body whilst the bogie is removed.
When the lifters are not in use, a clear, unobstructed workshop floor is available.
The alternative method is the use of multiple railcar jacks to lift the coupled vehicles. The whole train still enters the depot as in the first method, but in this case the jacks stand each side of the train and are engaged to the vehicle body at pre-determined points. Once the jacks are in position the controller facilitates a fully synchronised lift across all the jacks.
Both systems use screw technology as the basic lifting method, so offer a safe system for persons to work below and power requirements for both are very similar.
Underfloor systems provide a clear workspace when not in use, and importantly, a flat and level floor. No pit below the vehicle is required for staff to make the necessary disconnections to release the bogies as these are carried out when the vehicles have been raised on the lift tables. With the body supports in place, the bogie to be removed is lowered on the individual lifter, back to floor level and can then be pushed from below the raised vehicles for replacement.
Rail jacks do all the things required to facilitate a bogie change, but they do require a full-length pit below the train for staff access in order to make the disconnections of the bogie. Additionally, when not in use, the jacks will still be present in the workshop posing obstructions to other activities within the workshop. Trailing cables are usually associated with rail jacks, another major hazard in the workshop environment.
Considering the civil engineering requirements of both systems, the underfloor units require a pit of approximately 4.5 metres x 4 metres and to a depth typically of 3 metres plus, for each lifter, which results in a requirement for 540 cubic meters of pit construction for a five-car lift system. A full-length access pit for a jack system will be approximately 1.2 meters x 1.2 meters deep x 130 meters long, which produces a considerable saving on civil costs totalling only 190 cubic meters.
Trailing cables on multiple jack systems are no longer the problem they have been in the past. Where the jacks will be working in a set position, as in a comparable case with underfloor systems, the jack cables would normally be installed into ducts or conduits installed in the access pit.
There is no disputing the fact that the jacks will always be present above floor level, and this may pose a problem, however maintenance roads within a depot environment are intended to house vehicles undergoing maintenance, therefore it would seem there is no advantage for either system once the workshop is empty of trains.
Also the underfloor system has itself some disadvantages. Consider the implications of the train operating company requiring an extra vehicle to be added to the train. This is not an unusual occurrence, but the impact when related to an underfloor system would mean the provision of two more pits for the additional lifters, with all the associated cost and disruption.
These pits obviously have to be in the maintenance road of the depot, so whilst the new pits are being provided, and the lifters installed, the road is totally out of commission. This is likely to have serious repercussions for the operation of the depot. The requirement for an additional vehicle to be lifted would have little effect on a system of jacks, in that four new units could be set to work with no interruption to the working of the depot.
Although it is normal for both underfloor and jack systems to have fairly large and fixed control cabinets, there are railcar jacks now available with a distributed control system, which requires no fixed control cabinet. This system provides all the necessary control plus diagnostics in a portable unit the size of a small brief case. Jacks with this system provide the maintainer the facility to move the jacks anywhere within the depot, or should the need arise to transport the whole system to another depot for an emergency lift.
Although both systems have an excellent reliability record, what happens if a problem does occur? The underfloor system usually has a mechanically linked system of four screws operated by one or a connected pair of motor/gearbox units. Single screw failures are thus virtually unknown. Any failure of any lifter will result in the total failure of the entire system which could strand a train in the raised position. Recovery to allow repairs can be extremely difficult.
A failure of an individual railcar jack will also be extremely inconvenient. However a spare jack can be easily brought in to replace the failed unit permitting normal operations whilst the failed unit is repaired.
Author: Mechan, Published: 09 Nov 2015, Last Modified: 04 Nov 2015
Summary:This article discusses the respective merits of both Underfloor and Jacks for train lifting environments.