I'm told there was a discussion about this topic on this forum in the past. I searched and was not able to find it. Would someone be able to point me in the right direction? I was told changing to freight valves results in jerky brake applications because freight valves are not being released gradually. But UC and D-22 values are getting difficult (and expensive) to recertify. Any thoughts?

Welcome to the interchange.

If you use the search function with “ABDX Valve”, without the quotes, you’ll find some topics where this was discussed.

PABCO still services both UC and D22. There are still a lot of D22 cars out and about. The conversion to ABDX can save a bit of money in the long run. They have a longer service interval and are less expensive to maintain. If the car is over 75’ long, you’ll need the ABDX-L variant.

With a short train in low speed tourist service, you won’t need or miss the graduated release. Even when we ran excursions on the main, our cars were run in freight mode, anyway.

It may not be as simple as it sounds. Be sure you have someone who knows how brake design is done. You need to be sure that after the conversion you still have the proper brake ratio.

Well I guess it depends on whether you consider your operation a "museum" vs a "tourist RR"

I personally don't like the idea of hacking up a historic car, and especially replacing equipment with a modern equivalent of *nothing* it ever would have carried! ABDX is a freight system. If you think about what the original RR might have done if the car stayed in service another 50 years, what about 26?

Even that being said, Strasburg is still running with P triples! And they do contract work. Last time this came up, they were contemplating getting into the UC-12 stuff.

"Modern Freight Car Air Brakes", by David G. Blaine (Simmons-Boardman, 1979) has a section, with drawings, on 'Large brake cylinder volume-Relay valve equipment', which should also cover the conversion for passenger equipment. This is on pages 150 and 151 of the Blaine book. I have personally seen this conversion applied to several cars; crawled under them and verified the pipe connections, in fact.

The RB-B&B Circus Train, running maybe 60 cars, with both freight and passenger equipment, was equipped with direct release ABDW equipment. I have a good friend, a soon to retire NS engineer, who handled that train a few times. He did mention that there was a Bulletin Order that mentioned the direct release. Knowing that, he said that he ran the train just as he would have run a similar sized freight train, and at the same speed.

I'm curious about the comment regarding brake ratio, which I've seen before in other places. Replacing the control valve is only changing the source of the air. It is not changing the size of the brake cylinder, or any levers or brake rigging. A 10 pound brake pipe reduction will result in a nominal 25 PSI cylinder pressure, regardless of whether the application is through an ABDW, UC or D-22 valve. This is like asking a microwave to differentiate between 115 VAC coming through a GE circuit breaker, as opposed to one from Westinghouse; it should make no difference.

One thing more, added as an edit- I took a look at some commuter coaches that SEPTA was having scrapped a few years ago, with an interest in acquiring some of the air brake valves for a museum group I belong to. These particular cars were equipped with Knorr brakes, Knorr being the current owner of New York Air Brake. I was told by another museum member that unlike older NYAB and WABCO valves, which can be serviced by many vendors, only Knorr will service Knorr valves, and service is very expensive! There is a lot of Knorr DB-60 equipment out there, but older WABCO or NYAB ABDW components are a far better bet.

The Everett Railroad, which is a freight and tourist railroad, not a museum, is running ABDW and ABDX freight brake systems on all of our passenger equipment. The freight brake systems do take a little longer to apply and release than most passenger systems do. This may be why the original poster has heard claims of jerkiness. I could imagine certain mixes of passenger and freight valves in the same train might lead to slack action on application and/or release.

ABDW and ABDX valves are more readily available, cheaper and easier to get serviced, and have a longer service interval than most passenger equipment. This is why the Everett Railroad elected to switch to freight systems as passenger cars were restored.

Lack of graduated release is not an issue for us.

I can see how a museum, whose primary concern should be for the integrity of the artifact, might be hesitant to remove a historically accurate brake system in favor of a modern brake system with the above stated advantages.

For those wishing to keep historic passenger car brake systems in service, HRA, in conjunction with RPCA and FRA, came up with guidelines which allow operators of cars with historic passenger brake systems a little bit longer between service intervals, as long as certain conditions are met and certain documents are maintained.

https://heritagerail.org/wp-content/upl ... -10-22.pdf

Jason Lamb
Everett Railroad
Running freight brakes on passenger cars since 2013
Not a museum

This comment is incorrect in particular for ABD variants and UC.

"Replacing the control valve is only changing the source of the air. It is not changing the size of the brake cylinder, or any levers or brake rigging. A 10 pound brake pipe reduction will result in a nominal 25 PSI cylinder pressure, regardless of whether the application is through an ABDW, UC or D-22 valve."


These two schedules rely on volume equalization. In fact the UC manual has a table that outlines specific chokes and reservoir volumes for specific brake cylinder volumes.

Just as on freight car systems with large cylinder volumes the ABD variants require a 900 cu. in. dummy cylinder volume and relay valve for proper operation. Also there is no service limiting feature which can be accomplished with the integration of an H relayair valve and safety valve.

As for the Knorr DB series of valves I have found them superior as they use rubber seated poppets much like the 26C/F control valve instead of the lapped slide valve of the ABD series. The latest incarnation also incorporates brake cylinder maintaining.

EBL

The Blaine drawings that I referenced do include an 800 cubic inch dummy reservoir, and a J-1 relay valve. Perhaps I should have mentioned this in my earlier post. I was not suggesting a 'one for one' control valve exchange. There is more involved than just valves.

Jason, thanks for pointing out that document, which was an important development to come out of the HRA's work in 2022.

A little off topic but, for those who are interested in continuing to run their "as built" valves,
here at the East Broad Top we do offer service and testing of UC valves on our two UC test racks. We are also capable of servicing and testing K,P and L type triple valves on our 3-T rack. Our AB rack, we hope to have set up soon to start doing D-22 and we have a 6-ET rack "in transit" which will eventually enable us to offer locomotive brake servicing as well.
Anyone interested in recieving more information or a quote please email me.

rfreitag@eastbroadtop.com

Ron Freitag
Chief Car Inspector
East Broad Top Railroad/EBT Foundation Inc.