Passenger Trains > Decelostat Question

Over the years, I have noticed that almost all of the former ATSF passenger cars were equipped with decelostats, mainly on cars with outside swing hanger trucks. I know that these devices have something to do with anti-skid braking, but have often wondered how they worked.

I have also noticed that they were removed from the ATSF Hi-Level cars, and other ex ATSF cars including the BNSF Business car fleet. Have they been replaced with a similar device, or are they just not needed anymore?

Does anyone know the answers to these questions?

Thanks, Larry (SWChief)

We still have them on our passenger equipment. I know I should, but I\'m not precisely sure how they work. I know they have an adjustment that allows the mechanical forces to change the settings. They can sometimes be a royal pain on wet or slippery track. From the cabcar with the window open when you come to a stop at a station, you can hear them allowing little jets of air out as you come to a stop. They\'re designed to prevent wheel slip during braking. If they\'re not adjusted properly, or not working, they can cause flat spots in a heartbeat.

The old style mechanical decelostats that were prevelant from the late 40\'s onward operated on the principle of a flywheel. There\'s a spline that goes into the center of the axle. When the wheel/axle turned, the spline went in to the decelostat housing and turned a large flywheel. There is/was a mechanical sensor that could detect if the wheel/axle locked up, or slowed down revolutions in comparison to the flywheel. When this was detected, the decelostat on the axle would send an air signal (by the hose comming out of the side of the decelostat)to the decelostat contol valve usually located on the inside or outside of the truck. UP cars usually had the contol valve located near the truck cutout cock on the carbody. When the contol valve recieved the signal from the decelostat on the axle, it would momentarily dump the air from the brake cylinder line for a split second so the wheels would start turning again and not slide. You could hear these "Pop Off" quite a bit repeatedly during heavy brake apllications. It was a pretty simple system.

The newer/modern decelostat systems that Amtrak has uses the "Teeth" that are mounted on the rotating endcaps on the roller bearings. There is a sensor that\'s mounted through the jounal box, usually located in the 5 or 7 o\'clock position, that "reads" the "Teeth" as the axle turns. There\'s a close tollerence, I beilive that\'s several 64ths of an inch from the sensor to the teeth. The teeth are counted electronically and is transmitted to the control unit in the electric locker. The control unit then dumps the air in the same manner as the mechanical system. It operates off of battery power from the car, so if the HEP is lost, it\'s still fucntional while there\'s battery power.

That\'s the downfall of the Electronic System. This is the reason that most privately owned cars, even cars that had the Electonic System, have reverted to the older Mechanical Systems because of having to move in freight service whithout electric power. I have worked with friends at AOE in helping them obtain parts to convert their cars back to the mechanical systems.

I\'ve over simplified these two systems in hopes of giving a basic understanding of how they work and their differnces.

I have pictures of the different styles of decelostats and will post when I find them.

Harry

There is a speed sensor on each wheelset, which is read by a central computer on each car. The computer looks at the speeds, and if it sees a significant difference between the axle speeds, or if it sees a sudden deceleration of any or all axles, it knows that one or more wheels is sliding. The system then partially releases the air in the brake cylinder to allow the wheels to start turning again, then reapplies the air for braking.

These systems are particularly necessary on equipment with disc brakes, so if you saw them removed from some equipment, they have probably just applied a newer system that uses a different wheel speed sensor. The newest systems are so fast that they can cycle the brakes perhaps a dozen times a second, to ensure the best braking effort and wheel protection is provided.

Had to capture this from video so it may not look too sharp, but it gets the idea across.

Did these decelostats use Hall Effect switches? I know that the Hall Effect was based on magnetism, and that the switches were used in applications where a very high frequency impulses were to be detected.

At the spacing of these teeth, I can expect that the impulses would be in the range of 400-600Hz at 60-80 MPH.


Kevin

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Thanks to everyone for their informative info.I have learned a lot about a subject I have wondered about for a while.

Larry

SWChief wrote:

>
> I have also noticed that they were removed from the ATSF
> Hi-Level cars, and other ex ATSF cars including
>

Santa Fe was very anal about using hard steel for wheels and maintaining decelostats and proper wheel tread profile. If Amtrak cared about passenger comfort, they would do the same. This would include keeping all of the splendid ex-ATSF Hi-Level cars in service. Bob

The decelostat also has a door function. If a door or doors are accidently left open the decelostat has a speed sensor that will trip a zero speed relay that will shut the doors. It will close one door or all of them if needed. The decelostat kind of works like the anti brake system in automobiles. It will pump the brakes when it measures a difference between the speed of two axles. This release of the brakes only lasts for a few seconds and is reapplied. This goes on till the wheels catch up with each other to prevent flat spots on the wheels. Also any one who works on cars out there. I have found that any kind a welding done on a car wihtout disconnecting the decelostat can cause damage to it. At least to the WABCO units I am familiar with.

There are three types of anti-slide systems that I know of:

Decelostats, a WABCo registered trademark.
Rollokron, a Budd trademark (probably also registered).
The electronic versions used by Atk etc. - - can\'t recall the trade name.

Both the WABCo and Budd systmes use a spline-drive adapter on the end of the journal.

The WABCo 3-AP Decelostat, which is advertised as "Mechanical-Pneumatic", has an internal counterweight in the housing attached to the end of each axle). An axle which slips or slides sets up an imbalance between its rotational speed and that of the counterweight, tripping an attached pilot valve which then triggers a relay valve to reduce the brake cylinder pressure on that axle. There is absolutely no electricity involved at all. The SP used these.

Budd Rollokron accomplishes the same ends by using small electrical generators on each axle instead of the rotating counterweight and a set of magnet valves in place of the relay valves. Any axle which slips or slides rotates more slowly, generating a lower voltage. The volage imbalance is detected by the magnet valves which momentarily reduce the brake cylinder pressure to the affected axle. I seem to recall that this system ties all the axles together in the sense that if all the axles were sliding, it wouldn\'t be detectable because there would be no voltage imbalances (with Decelostats, each axle acts independently of the others). I\'m not sure if this system needs electricity from the car battery (etc) or not, although I suspect it doesn\'t. The Q and CZ used Rollokron.

The "Atk system" uses the serrated ring speed sensor on the end of the roller bearing (see photo on previous posting) and onboard electronics (read "computer", which really is a "black box"). The sensor counts the teeth as the axle rotates, and this information is translated into a speed signal by the computer, which regulates slow rotating axles by reducing the brake cylinder pressure (with magnet valves). Being a computer, and therefore subject to the addition of all kinds of bells and whistles, not to mention all the inherent computer-realted foibles, this is the least reliable.

The word "decelostat" has become generic, much like "kleenex".

Once again, thanks to everyone for their contributions.This is a great forum,in that people are willing to share their expertise on such a broad range of Railroad subjects.

Larry

InsideObserver wrote:

> There are three types of anti-slide systems that I know of:
>
> Decelostats, a WABCo registered trademark.
> Rollokron, a Budd trademark (probably also registered).
> The electronic versions used by Atk etc. - - can\'t recall the
> trade name.

There are two electronic systems. Wabtec offers Decleostat, and Knorr-Bremse offers a competitive system. The current Wabtec system is their second generation electronic system, model E-7