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 Railway / Railroad Products Freight Wagon (Car) Speed Control and Frog Dampers Ultra Dynamics, formerly a division of the Dowty Group of the United Kingdom, has designed and manufactured piston retarders for controlling the speed of freight wagons in marshalling yards (also known as freight cars and switching yards) since the mid-1960's. Ultra’s Piston Retarders are commonly called “DOWTIES” in North America. Ultra Dynamics also designs and manufactures hydraulic frog dampers for main-line and siding switches. Ultra Dynamics has BS EN ISO 9001 certification (since 1994).
Goals – Avoid Freight and Equipment Damage - Improve Switching Yard Productivity
• Controlling car (wagon) speed, especially when coupling in the class tracks. • Maintaining separation of freight cars (wagons) down the leads and tangent tracks. • Reducing risk of derailments and subsequent damage to cargo, rail cars (wagons), and rails.
Video of Cars Coupling (Large - 1.7MB) (requires QuickTime) Video of Cars Coupling (Small - 643k) (requires QuickTime) High Capacity (HC) Piston Retarders Used in marshalling (switching) yards to control the speed of wagons (freight cars) as they leave the hump and enter the class tracks. The Ultra HC piston retarders are bolted to the rail web. A quantity of retarders specified for the desired speed control are installed along one or both rails, between the sleepers. This grouping of retarders is called a “zone.” Each retarder is factory-set for the specified wagon speed, typically m/sec (6 mph) for the lead and 00 m/sec (4 mph) for the class tracks. Other speed settings may be specified. Operation: As the wagon (freight car) rolls over the HC piston retarder, the wheel depresses the piston. If the car speed is lower than the retarder’s speed setting, the piston offers no resistance. If the car speed is at or greater than the speed setting, an internal valve is activated to provide a resistance to the wheel, thus slowing the wagon. If necessary, energy equal to the sum of all retarders in the zone is removed thus keeping the wagon at the designated speed. Specification Installation drawing Video of HC operation (requires QuickTime)     Project Engineering Assistance: Ultra Dynamics offers project engineering support to verify quantity of retarders, number of zones, grade recommendation, car separation, throughput analysis, and on-site inspection. Please complete and return questionnaire to initiate support. Yard Project Questionnaire Ultra’s TrackMaster (TM) Piston Retarders Operation of the TrackMaster piston retarder is similar to the HC above, however, construction differs with a larger diameter piston and higher gas and fluid capacity. This achieves a flatter energy curve with less risk of wheel lift. Like the HC, the TrackMaster is used in marshalling (switching) yards to control the speed of wagons (freight cars) as they leave the hump and enter the class tracks. The Ultra TM piston retarders are bolted to the rail web. A quantity of retarders specified for the desired speed control are installed along one or both rails, between the sleepers. This grouping of retarders is called a “zone.” Each retarder is factory-set for the specified wagon speed, typically m/sec (6 mph) for the lead and 00 m/sec (4 mph) for the class tracks. Other speed settings may be specified. Operation: As the wagon (freight car) rolls over the TM piston retarder, the wheel depresses the piston. If the car speed is lower than the retarder’s speed setting, the piston offers no resistance. If the car speed is at or greater than the speed setting, an internal valve is activated to provide a resistance to the wheel, thus slowing the wagon. If necessary, energy equal to the sum of all retarders in the zone is removed thus keeping the wagon at the designated speed. Specification Installation drawing Video of TM operation (requires QuickTime)    Project Engineering Assistance: Ultra Dynamics offers project engineering support to verify quantity of retarders, number of zones, grade recommendation, car separation, throughput analysis, and on-site inspection. Please complete and return questionnaire to initiate support. Yard Project Questionnaire Ultra’s Retractable Piston Retarders The Retractable piston retarder utilizes the basic HCR piston retarder (described above) along with a pneumatic cylinder used to positively retract and hold down the retarder piston. The Retractable retarder is used when positive hold-down is required, such as when individual wagons, or a complete train needs to traverse the retarder zone. With the hold-down pneumatically actuated, the wheels do not contact the retarder pistons. Air pressure to operate the hold-down feature can be provided from a central yard pneumatic system or by smaller local air compressor powered by yard AC electric current. With either method, the hold-down feature is actuated by electrical signal from the yard operations center. Specification Installation drawing Video of Retractable Retarders operation (requires QuickTime)     Project Engineering Assistance: Ultra Dynamics offers project engineering support to verify quantity of retarders, number of zones, grade recommendation, car separation, throughput analysis, and on-site inspection. Please complete and return questionnaire to initiate support. Yard Project Questionnaire Ultra’s Vacuum Hold-Down Piston Retarders The Vacuum Hold-Down piston retarder is an alternative to the Pnuematic Retractable hold-down described above. There are two variations, both with the hold-down feature actuated by an electrical signal from the yard control
This simple version relies on air being expelled via a solenoid-operated check valve when the wagon wheel depresses the retarder piston. The resulting low pressure in the housing limits the return of the piston between wheel actuation. Some air returns via the piston seals so each wheel taps the piston. Same as without, except that a local vacuum pump helps to retract and hold down the retarder piston. Each wheel rolls over the retarder without contacting the piston Ultra’s Hydraulic Frog Retarders Frogs are the moveable rails in switches used to divert rail cars and trains to a another track. The frogs are typically spring-loaded to the closed position and are pushed open by the passing wheel flanges. Without Ultra Frog Retarders, the frog would slam shut under spring force after the wheel has passed. If this were to happen with every passing wheel, the frog and switch would soon self-destruct. The Ultra Frog Retarder acts as a spring damper to slow the closing speed of the frog to 25 to 30 seconds. The frog then stays open for the duration of the train passing, with each wheel tapping the frog. Specification Installation drawing   
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