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Hydraulic Dampers Help Improve Railway Safety and Stability

Oct. 21, 2019
Technological developments in railway suspension sealing products and materials offer several operational advantages.

As demand and investment in the global railway market grows, so have needs for railway components and equipment. Locomotives, passenger and freight cars, wheels, axles, and brakes are among numerous essential parts manufactured by equipment suppliers for railways.

Hydraulic dampers are a primary part of the suspension system of a railway bogie, or coach. They are invisible to passengers, but their presence is evident as they sustain the weight of a train to reduce vibration and railcar wear for increased stability and comfort. Assembled inside each hydraulic damper is an arrangement of seals that allow the mechanism to absorb shock impulses.

How can seals help railway hydraulic dampers (or shock absorbers) perform most efficiently in three areas that matter most to operators—load, friction, and speed? We will attempt to answer this question by first examining how these important mechanisms work.

All About Railway Dampers

A hydraulic railway damper is a device designed to absorb and reduce shock impulses incurred when a railcar is in motion. Dampers also help reduce noise and track wear. They operate on diesel and electric locomotives, passenger mainline coaches, and diesel and electric multiple-unit trains.

Assembled inside each hydraulic damper is an arrangement of seals.

Steel, cast iron, and aluminum are the primary metals used in constructing railway dampers. The average life span of a damper is three years, and in some instances, a bit less. Manufacturers continuously refine and improve the application of materials in the construction of railway dampers to equip them to withstand long, demanding work periods. Material and design innovation promote longer product life. As a result, railway operators benefit from reduced downtime and costs due to damper repair, overhaul, and maintenance. 

Railway car suspension systems are categorized as primary and secondary. The primary system consists of vertical dampers fitted between the railcar wheelsets and the bogie frame. Secondary hydraulic railway dampers fit vertically and laterally between the bogie and the railway car. This system includes a yaw damper configuration for shock absorption and to prevent excessive swaying.

Hydraulic dampers designed with PTFE seals play an important role in a railway bogie’s suspension.

Interestingly, the sealing systems designed into a railway damper play an important role in ensuring its ability to perform as intended. Let’s review some important characteristics to consider when selecting seals for a railway suspension system.

Load, Friction, and Speed

Load-carrying capacity for a railway suspension system accounts for the weight, height, and width of a railcar to ensure its capacity for the safe and stable transport of people and goods. During the hydraulic damper design, shock absorber manufacturers and sealing suppliers collaborate on seal specifications and materials custom-suited for carrying various freight.

Also, to meet industry requirements and address a trend towards increasing axle load for greater transport capacity, operators must adhere to local, national, and international standards. For example, the Association of American Railroads (AAR) is one organization that helps sets standards for freight cars in the U.S. The International Union of Railways (UIC) supports the development of standards worldwide.

Friction plays a major role in the function and life of a railway damper. When balanced, it helps prevent leakage on rod seals moving at a speed of 0.7 m/sec (1.6 mph). Most seals manufactured for the device are designed to endure up to 1.2 million km (746,000 mi) of use, which is generally a life of four to five years. It is important to note that the amount of force generated from friction in railway shock absorbers pales in comparison to the total damping forces.

As railroad speeds increase, dampers and their sealing components must be equal to the task. For example, the Gatimaan Express is currently the fastest train in India, operating at a speed of 160 km/hr (99 mph). Depending on the route, distance, and track conditions, several trains in the country run at speeds between 100 to 150 km/hr (60 to 90 mph). Plans are currently underway in India to construct 10,000 km (6,200 mi) of new speed corridors to run trains at 200 to 250 km/hr (120 to 155 mph). With the upgrading of existing rail lines and the initiation of new rail construction projects worldwide, speed will be a constant factor to consider.

A Case from the Field

A major global manufacturer of rail components operating in India sees a significant improvement in the durability of one of its damper products because of innovation in sealing material technology.  Seals constructed in Hallite proprietary Armorlene PTFE materials and compounds and Hythane TPUs (thermoplastic polyurethanes) replaced an incumbent Teflon PTFE seal. Sealing products constructed in these high-performance materials offered greater longevity than their predecessor. The manufacturer’s state-of-the-art product testing facilities confirmed the sealing material’s ability to handle the operational requirements.  Hallite seals passed the customer test requirements of 10 million endurance cycles, 1.2 million km run of train, and temperatures sustained at −40 to +80°C (−40 to 176°F).

The supplier prescribed a high-performance combination of seals composed of four key products:

Piston seal—The Hallite’s P54 is a double-acting, O-ring-energized, low-friction piston seal. Its wear, extrusion-resistance, temperature, and media compatibility are well-suited for the demands of the railway damper. The P54 seal face employs notches that make the seal responsive to changes in pressure and travel direction.

Rod seal—The R16 rod seal is a single-acting, O-ring-energized, low-friction rod seal. It is designed for tandem installations and optimum sealing in high-speed applications like railways. The R16 is a pressure buffer seal that protects the primary rod seal from high-frequency pressure spikes.

Wiper seal—The Hallite’s E5W is a double-acting, O-ring energized rod wiper seal designed to keep dirt and contaminants out of the cylinder. It includes two different wiping lip geometries that scrape debris from the rod, contains residual oil on the
rod extension, and allows oil to pump back into the cylinder. This seal is suited for
high-speed applications and various temperatures and fluid media.

Bearing strip (guide ring)The 506 bearing strip offers a hard-wearing solution for reciprocating, oscillating, and slow rotary movement applications. It can withstand extreme side loads and prevent metal-to-metal contact between the piston and the rod and the gland.

As new hydraulic sealing products and materials become available, manufacturers rely on knowledgeable, experienced suppliers for the latest developments. Testing will become increasingly important, and this was the case for the global railway component manufacturer. After the prescribed sealing products passed the company’s rigorous in-house testing regiment, they were accepted. Test results help build confidence in product integrity and ensure adherence to acceptable production standards.

This information was submitted by Bansidhar Gaur, managing director for Hallite Sealing Solutions India. For more information, e-mail him at [email protected] or visit hallite.com.

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