What is in this article?:
- Cartridge valve manifold makes light work of lifting
- Simplified functionality streamlines operator control
Railroad cars carry huge loads, typically 250,000 lb. That capacity makes them very economical for long-distance freight transfer. But until the 1950s, moving rail cars very short distances — such as from one track or train to another — was costly and time consuming. The procedure required a conventional switching locomotive, an engineer to operate it, and a switchman to assist.
Then, in the late 1940s, Trackmobile Inc., introduced its mobile rail car mover. This vehicle drives around the railyard on rubber tires to the rail car location and positions itself over the tracks. It then lowers a second set of wheels, made of steel, onto the rails. Using a special coupler, it attaches to the rail car and moves it to its new location. The movers’ ability to relocate rail cars more simply and efficiently made them popular workhorses.
Heavy lifting with hydraulics
The rail car mover transmits drivetrain power through a torque converter and transfer case. A pressure-compensated hydraulic system operates hydrostatic steering, wheel lifting and lowering, and coupling. However, the coupling procedure is not quite as straightforward as it seems. The rail car mover’s power approaches or equals that of a conventional switching locomotive, but its light weight generates much less traction against the steel rails. To improve traction, the coupler uses hydraulic power to lift the front end of the rail car slightly, transferring some of its weight to the rail car mover.
The lifting action requires care because it is possible to lift the front end of the car completely off its truck. (A simple vertical pin makes the mechanical connection between the rail car body and its truck.) Too little lift produces insufficient traction; too much lift can cause separation. And the rail car may be full, partially loaded, or empty.
Electrohydraulics offers smooth control
In the 1990s, Trackmobile modernized and streamlined the weight-transfer function on its Magnum line with a combination of rugged microprocessor controls and electrohydraulic valves. The patented Max-Tran autolift system eliminated operator guesswork and ensured appropriate weight transfer and tractive effort. The system consisted of a controller, pressure transducers, control panel switches and indicators, and software, supported by an electrohydraulic cartridge-valve manifold.
The basic concept of the Trackmobile rail car mover hasn’t changed from the Magnum series to the current Titan, Hercules, and Viking Series. The same solenoid operated, hydraulic cartridge valves used on the Magnum series are still in use on the three new series. The integrated circuit is manufactured by Parker Hannifin, but the original valves were not. Because they are so close in design, the newer valves are anodized red instead of the original blue, to distinguish the two. Simply put, the reason for staying with the same valves for so long is that they work so well.
The hydraulic integrated circuit incorporates SV3A-10 solenoid-actuated directional valves and PR3B-10 pressure-reducing/relieving valves, rated for 3600 and 5000 psi, respectively. These cartridge valves are designed and built for low leakage and long life. The directional valves control the cylinders that raise and lower the road wheels and those that position the coupler up, down, left, and right.
A transducer monitors pressure in the coupler’s lifting cylinder, and application-specific software translates that pressure into tractive force. When commanded, the controller adjusts the output pressure of the hydraulic system supplying the coupler. This limits the height to which the rail car can be lifted. The controller’s closed-loop system ensures safe operation. It also adjusts for the weight of the rail car as well as the inevitable variances in track elevations, including dips and hills.
Another aspect of the Max-Tran electronic package — jointly designed by Trackmobile and suppliers — adds anti-lock braking and traction-control functions to the machine. It is now designed and manufactured by Class1, Ocala, Fla. (www.class1.com), according to Trackmobile’s specifications. By monitoring wheel and ground speeds, and comparing them to a predetermined ratio, the control will automatically pulse the brakes and/or the wheel torque to keep the rail car mover travelling smoothly. The versatile package also allows Trackmobile to offer radio remote control as an option.