What happens when you’re off the air?

Written by William C. Vantuono, Editor-in-Chief
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Air brake technology is improving. Do FRA brake test rules need updating?

Freight train operations continue to evolve—specifically, longer heavier consists running in all kinds of weather conditions and ambient temperatures—and air brake technology is evolving along with it. Though regulatory issues involving PTC and tank car safety have been capturing most of the attention, air brake R&D continues quietly in the background. Here’s a look at what’s being examined at present.

IAROO, ABA BNSF 90 CFM Test Waiver

At Railway Interchange 2015 in Minneapolis, the International Association of Railway Operating Officers (IAROO) and the Air Brake Association (ABA) held a joint session to discuss the BNSF Railway’s 90 CFM pilot test waiver.

Jeff Garrels, Director of Train Handling at BNSF, explained that the need to increase from 60 CFM to 90 CFM for DP (distributed power) operations is specifically meant for extreme cold weather, such as on the railroad’s Northern Hi-Line route, Minneapolis to Whitefish, Mont.

Current Federal Railroad Administration and previous Transport Canada air brake rules limit train line air flow not to exceed 60 CFM for an entire train, including DP units, with no more than a 15 PSI brake pipe pressure gradient between the head end and the rear end. These requirements have been in place since 1984 in Canada and 1989 in the U.S.

According to Garrels, one advantage of DP is “the ability to charge and maintain the brake pipe with multiple air sources, distributed throughout the train.” In 2009, CP and CN began testing 90 CFM, which was approved in Canada in November 2011. Calculating data from the Canadian railroads, BNSF began 90 CFM Waiver testing in Great Falls, Mont., in August 2012. The intent is to establish FRA waiver criteria for increasing air flow limit to a maximum 90 CFM combined on DP trains.

BNSF’s 90 CFM Waiver testing generated the following results and observations:

– 90 CFM brake pipe pressure did not adversely affect GE LOCOTROL® Communication Interruption recovery protocols, nor were there any negative impacts on overall air brake functionality under certain conditions of DP and train segment lengths.

– As temperature decreases, air flow increases. This was specifically seen at temperatures below 0 degrees F.

– No difference in DP performance across various train types.

– Brake applications and releases ranging from a minimum reduction to a full-service application were made without any problems at brake pipe leakage rates for 60 CFM and 90 CFM.

– No significant differences were noted between the brake applications made at 90 CFM vs. the brake applications made at 60 CFM or in between.

– Several trains did exceed 90 CFM but were secured until air flow resided. “Testing conducted thus far has validated our theory that air flow rates can be increased from today’s maximum of 60 CFM to reach as high as 90 CFM combined on DP trains and still allow continued safe train operations,” Garrels said.

BNSF provided a waiver update to FRA, and in September 2015, the railroad submitted this update to FRA for admission to docket. In addition, a Waiver Subcommittee has been formed to assist this effort. The Association of American Railroads is helping to facilitate the process. The test waiver, Garrels said, has been extended until 2017, and in the interim the railroad “will continue to operate under the waiver in place, as it offers operational benefits during cold weather. The Waiver Subcommittee is actively working with AAR to finalize a petition for proposed change in regulation and its subsequent submission to the FRA.”

Time off and cold temperatures

For U.S. operations, the Code of Federal Regulations stipulates that Class I brake tests (initial terminal inspections) and Class II brake tests (intermediate inspections) be conducted on cars that have been disconnected from a source of pressurized air (“off air”) for more than four hours before they are moved in a train. This time limit was codified in 2001, providing an increase from an “administrative interpretation” that had allowed a maximum of two hours off-air, increasing it to four.

In describing its justification for the higher time limit, the FRA stated that it “tends to agree that the amount of time equipment is left off a source of compressed air is not directly related to the operation of the brake system on that equipment. However, FRA does believe that in certain circumstances the length of time that equipment is removed from a source of compressed air can impact the integrity and operation of the brake system on a vehicle or train. Particularly in cold weather situations, where freeze-ups in train brake systems can occur… if equipment were allowed to be off-air for an excessive amount of time, it would be virtually impossible for FRA to ensure that equipment is being properly retested, as it would be extremely difficult for FRA to determine how long a particular piece of equipment was disconnected from a source of compressed air.”

In 2008, the four-hour limit was increased for trains equipped with ECP (electronically controlled pneumatic) brake systems to between 24 and 80 hours, depending on where the train is parked. For example, if such a train is parked at an “extended off-air facility” such as a fenced-in power plant, FRA allows up to 80 hours without requiring a retest.

The No. 1 and No. 1A brake tests required by Transport Canada are similar in procedure to FRA Class I and Class II tests, respectively. These tests also establish off-air time limits, but the maximum allowable off-air time without retesting is 24 hours.

Since FRA last considered the question of changing the off-air time limits for non-ECP equipped trains in 2001, “a number of changes in the industry have occurred,” TTCI says. “Railroads have increased the use of information technology systems to track off-air time, which should alleviate concerns about regulation enforcement difficulty. Increased use of wayside wheel temperature detectors to monitor brake system health allows for the ability to identify cars with poorly performing brake systems without a visual inspection.

To support the AAR SRI (Strategic Research Initiative) on brake system performance, Transportation Technology Center, Inc. (TTCI) conducted testing to evaluate the effects on freight car brake system performance after being disconnected from a source of pressurized air for different periods of time during winter weather. Using a block of 20 coal gondola and hopper cars, TTCI conducted Class I brake tests 10 times over the course of five days. The air flow and leakage rate tests were used to evaluate the brake pipe pressure leakage. Brake cylinder pistons and brake shoes were checked on each car to ensure that the brakes applied in response to a 20 PSI brake pipe service reduction and again to ensure that the brakes released when the brake pipe pressure was increased. After each test, the gladhands were uncoupled between the locomotive and the first car to allow ambient air to infiltrate the train line as it would in a revenue service situation. Air temperature at the time of the tests ranged from 17 to 57 degrees F.

“There was no change in the brake system performance of any of the 20 cars throughout the course of the testing, regardless of the air temperature or off-air time prior to the test,” TTCI said. “On all the cars, the brakes were applied in response to a 20 PSI brake pipe service reduction and released only when the brake pipe pressure was restored. A variety of brake pipe pressure leakage rates were recorded, and all of the values met the Class I test criteria. The brake pipe pressure flow rate and gradient values likewise met the Class I test criteria. Due to the measurable leakage in the brake pipe, the flow rate and gradient values must have been slightly greater than 0 cubic feet per minute and 0 PSI, respectively. However, on a short consist of 20 cars using typically available measurement devices (a flow meter on the locomotive and pressure transducers on the locomotive and end-of-train device), these values were too small to quantify.”

“Railroads are proactively pursuing improved brake system health monitoring through the use of wayside wheel temperature detectors,” TTCI stresses. “These devices allow an in situ evaluation of the brake system health of every car that passes the detector. Such methods are able to identify not only cars with inoperative brakes, but can also be used to identify cars with chronically under-performing brake systems. For example, while the brake cylinder may look fully pressurized to an inspector, it may only have sufficient air pressure to extend the piston and may not be providing the intended brake shoe force. Wayside wheel temperature detectors are capable of identifying the symptoms of this type (and other types) of poor brake system performance.

“Railroads have invested heavily in information technology over the past 20 years. Using commonly held technology, it should be possible to compute an estimate of off-air time for a car or cut of cars by querying the arrival time at the current terminal. Railroads utilizing AEI (automatic equipment identification) technology have the ability to research the time a car, train, or cut of cars arrived at a location and when it departed, without the need for a physical observation of the event.

NYAB and BCM

Brake cylinder leakage during train operations can create safety problems, and affect productivity. Brake cylinder leaks are caused by such environmental stresses as vibration and impacts; dirt, grime, oil, solvents and grit; moisture; and extreme temperatures. “For short-duration brake applications, such leaks are inconsequential, because the system quickly recharges after release,” notes New York Air Brake Team Leader, Valves and Foundation Equipment-New Product Development Derick Call. “The AAR Brake cylinder leakage allowance, per S-486/3.14 (Brake Cylinder Leakage Test), is no more than 1 PSI per minute.”

Recent data indicates that 90% of freight cars have some brake cylinder leakage. Exponential distribution results in an average 0.5 PSI per minute leakage across the AAR fleet. “On long downgrades and in winter conditions, small leaks become a bigger problem,” says Call. “Braking power diminishes with each minute, since the system cannot compensate on the fly. Safety and control are reduced. Wear and tear increases on brakes with smaller cylinder leaks as they attempt to ‘make up the difference.’ Wheels on cars with brakes that have lost their braking force become ‘cold’—which becomes its own problem.”

Across the U.S. there are more than 6,000 wayside hot/cold wheel detectors installed. “Originally introduced to detect ‘hot’ wheels—bad bearings—these systems now detect ‘cold’ wheels,” says Call. “The detector looks for and passes wheels of sufficient temperature. Warm wheels equate to ‘good brakes.’ Conversely, cars with ‘cold’ wheels (based on average) are flagged for service and repair, so cold wheels equate to ‘bad brakes.’ But cold wheel detectors are not infallible. Cars with good brakes can be flagged after downgrades. Many of them later pass the single-car test and are returned to service, resulting in lost productivity and unnecessary costs.”

New York Air Brake offers a solution to this problem: The The DB-60 II™ with Brake Cylinder Maintaining (BCM™), which compensates for common brake cylinder leaks by recharging the brake cylinder while the train is moving. “BCM works on long downgrades, and in cold weather conditions to improve the accuracy of hot/cold wheel detection systems,” says Call. “The benefits are more braking control, improved productivity, cars in service longer and reduced operating costs.”

On grade braking, BCM “provides the needed flexibility to handle a train with leaky brake cylinders,” says Call. “In addition to avoiding delays and lost revenue due to unnecessary stops, and reduced stress in the brake system due to brake cylinder leakage, there’s an added safety margin for unexpected events, such as loss of dynamic brake.”

A non-maintained brake cylinder will leak down to the 10 PSI QSLV (Quick Service Limiting Valve) level, “an unsafe level by any standard,” Call notes. “The DB-60 II with BCM will maintain brake cylinder pressure to within 8 PSI of the target pressure—what the pressure would have been with no leakage—at a rate of 1 PSI per minute (chart, p. 32). For 10 PSI of target pressure, the rate is 2 PSI per minute. NYAB has a simple concept to achieve the BCM function that can be used to easily upgrade existing valves. The 8 PSI offset is an inherent design characteristic. Other designs that would have been able to maintain target pressure could have been used, but they would have been impractical for upgrading current valves. BCM preserves up to 85% of the braking effort that would otherwise be lost to leakage.”

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