Ever wonder how freight cars are safely slowed down and sorted in bustling railway yards? A reel on Facebook went viral for a video of this railway equipment. Enter the Joule Piston or Hydraulic Retarder, an ingenious device that plays a crucial role in managing train speeds and ensuring smooth operations. Let’s explore how these marvels of engineering work their magic on the tracks.
The Basics of operation of railway retarders
Joule Piston Retarders are self-contained, hydraulically operated devices installed on railway tracks to control the speed of rolling stock. These retarders require no external power source, making them efficient and reliable tools for managing train speeds in marshaling yards.
They are effective speed retarders. After being plunged by a rail car, they immediately pop up with higher resistance to being pressed in again, so if the next wheel comes by too soon it applies more resistance against it.
How Railway Hydraulic Piston Retarders Work
The engineering design behind their technology is the kinetic energy principle.
$$E = \frac{1}{2}mv^2$$
where E is the energy extracted, m is the mass of the railcar, and v is its velocity.
1. Energy Extraction: As a railcar rolls over the retarder, it extracts energy from the vehicle. The faster the railcar moves, the more energy is extracted. As energy can not be destroyed, it is converted to another form of energy as heat, sound or vibration.
2. Hydraulic Mechanism: The retarder uses a pre-calibrated hydraulic system with specific flows and pressures. Hence, a hydraulic fluid is filled inside the piston and this fluid serves as a damper. A speed-sensitive valve activates at predetermined speeds.
3. Piston Action: When a railcar’s wheel flange passes over the retarder, it presses against the piston tube, forcing down the piston rod of the damper.
4. Speed-Dependent Operation: If the railcar’s speed is below the set threshold, the valve remains inactive, and the retarder “idles.” At higher speeds, the valve activates, extracting energy from the car and slowing it down.
Advantages of Joule Piston Retarders
– Versatility: They can handle all types of wagons with various cargo types at sorting stations.
– Flexibility: These retarders can be used for fastening rail cars on station tracks.
– Integrated Track Creation: By deactivating the cylinders, it’s possible to create an integrated track when used on station tracks.
The Applications of Railway Retarders
Joule Piston Retarders find their primary use in speed control systems on classification tracks for deceleration and coasting runs. They’re particularly useful in train formation yards, where precise speed control is essential for efficient and safe operations.
The design of retarders in railroad marshalling
Engineers calculate the design of Joule Piston or hydraulic retarders for railway tracks using a combination of simulation tools and empirical data. The process involves several key steps:
1. Retarder Simulation: Engineers use a Retarder Simulator to calculate predetermined flows and pressures for the hydraulic system. This simulation ensures that all setting parameters maintain efficiency during final assembly and calibration.
2. Engineers consider various parameters to determine the number and density of the retarders such as car weight, gradients, curves, rolling resistance, and space for their installation.
2. Energy Extraction Calculation: The retarder’s performance is based on energy extraction, which is speed-related. Engineers calculate the energy extraction using the formula:
$$E = \frac{1}{2}mv^2$$
where E is the energy extracted, m is the mass of the railcar, and v is its velocity.
3. Speed Setting Determination: Engineers determine the speed at which the retarder’s valve should activate. For example, a retarder might be set to extract 1180 Joules of energy at 4 mph which is the speed with which most railroad yards operate. (1.80 m/s, 6.4 km/h)[3].
4. Environmental Considerations: Designs must account for a wide range of operating conditions, including ambient temperatures from -40°F to 150°F (-40°C to 65.6°C), as well as rain, snow, and ice].
5. Noise Emission Calculation: Engineers calculate noise emissions, aiming for levels around 55 dB to make the retarders suitable for use near residential areas.
By carefully considering these factors and using advanced simulation tools, engineers can design Joule Piston or hydraulic retarders that effectively control train speeds in railway yards while minimizing noise and maximizing efficiency.
Sources:
[1] https://repo.journalnx.com/index.php/nx/article/download/3888/3724/7524
[2]]https://assets.new.siemens.com/siemens/assets/api/uuid:b09fc4aa-f417-4801-9bd3-7eee3d9abb97/rz-sie-trackguardretarder-broschuere-eng.pdf
[3] https://en.wikipedia.org/wiki/Retarder_(railroad)
[4] https://argent.co.za/subsidiary/new-joules-engineering/
[6]https://newjoulesengineering.com/info/documents-manuals-drawings/