The New Zealand Railways Magazine, Volume 1, Issue 8 (January 15, 1927)
Modern Shunting Methods — Part VII.—Gravity Shunting Yards
Undoubtedly the greatest change in shunting yard methods that has taken place in recent years is the general adoption of the “gravity” principle. This has been brought about by the fact that operating officers have been compelled by reason of the ever-increasing operating costs and the need for speeding up terminal work generally, to devise some means of ensuring more rapid handling of wagons at less cost. The largest item of expenditure is the locomotive. The first thing to be considered, therefore, is, can the locomotive be dispensed with; if not dispensed with entirely, can it be made to perform more work in a given time at less cost? The solution is found in utilising the force of gravity for shunting purposes.
With operating officers all over the world the gravity system for large marshalling yards is now a recognised necessity. Not to be behind the times New Zealand is now to have two gravity yards, and although the application is different in each case, the principle is being applied to the two new marshalling yards now under construction, viz., at Middleton near Christ-church in the South Island, and at Palmerston North in the North Island. The former is a “hump” yard and the latter “semi-gravity.” It might be of interest, therefore, to discuss in some detail the various methods of applying the gravity system for shunting wagons.
Many of my readers have heard a good deal lately of “gravity” and “hump” shunting, and no doubt the terms are somewhat confusing. The profiles in illustrations Nos. 1 and 2 are readily understandable and should dispel any such confusion. It is seen that there are three distinct forms of gravity shunting as compared with flat shunting, namely, all gravity, semi-gravity, and hump. The profiles should not be taken too literally; they are merely given for the purpose of explanation. The two illustrations of yard page 31 layouts, page 25 of the September issue of this magazine, show clearly the actual profiles of two yards. As regards the French yard shown, the peculiarity of the profile is due to the fact that this is a double hump. The departure roads, of course, are actually on the level, and only the wagons to be shunted go over the hump.
“All gravity” yards are economical only when handling large traffic. 1,000 wagons per day should be the minimum, the reason for this being that a number of separate grids or groups of sidings are required to make the necessary classifications, irrespective of the number of wagons, and unless there is constant movement, the output per road would not justify the capital and maintenance expenditure. Given the same number of classifications, a yard handling only 500 wagons per day would require the same number of roads as for 1,000 wagons per day. Furthermore, the same shunting staff would probably be required in order to ensure con-tinuity of movement from one grid to another. It may be argued, of course, that the shunting gangs could move about as required and work one grid before proceeding to another. In actual practice, however, where the rapid make-up of trains after the arrival of others is essential, this could not be done, and more gangs would be required. It is plain, therefore, in regard to the smaller yards that, before deciding upon the “all gravity” method, operating officers have to determine whether shunting engines with more flexibility of working, less page 32 shunting staff, and fewer roads would not be more economical.
As regards larger yards requiring, for instance, six engines, four working 24 hours and two working 16 hours each per day, there is no question but that by employing the “gravity” principle and dispensing with engines very considerable economy can be effected. The “all gravity” yard to perform the same service would be smaller, in that the working capacity of each road would be considerably increased by the very rapid handling of wagons. Furthermore, the elimination of engines would represent in this country an operating saving of approximately £24,000 per annum, excluding the wages of shunting staff, but including the wages of locomotive men, interest and depreciation and repairs to the locomotives. This would more than compensate for the additional expense in obtaining correct grades, installing electrical point operation and wagon retarding devices, and employing any additional shunting staff.
There are, of course, other shunting operations incidental to large yard working, but dealing with the marshalling and sorting of wagons only, the “all gravity” method can truly be said to dispense with engines.
As regards the possible damage to rolling stock it is a recognised fact that with the introduction of wagon retarding devices the damage to rolling stock is reduced to a minimum. The car shocks set up by the protracted backward and forward movement of long rakes of wagons which flat shunting necessitates is entirely eliminated. What shocks do take place are caused by negligence on the part of the staff and are avoidable, whereas with flat shunting they are unavoidable.
The increased safety of the staff is another very potent factor when considering the advantages of the “gravity” method of shunting. Movements are all straightforward. There is an entire absence of confusion, whilst, in the most up-to-date yards, jumping on and off wagons is quite unnecessary. Points are operated electrically, and wagons are braked electrically, consequently the shunter's job is confined to coupling and uncoupling wagons and chalking the road numbers on the front of the wagons to enable the signalman operating the points to see which road to set. (To be continued.)