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 Post subject: Brake Question
PostPosted: Mon Nov 15, 2021 6:39 pm 

Joined: Thu Oct 08, 2015 11:54 am
Posts: 1773
Location: New Franklin, OH
I’ll start by stating that I am in no way a brake expert. I know enough to get in trouble. The scenario is that our caboose won’t hold a set. Say we’re standing with a 20lb. reduction. The pressure gradually leaks off somewhere releasing the brakes on the caboose. This does not affect the train line as it holds pressure. The valve is an AB. I think the service portion of the valve needs serviced but is there anything else I should be looking at?

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Eric Schlentner
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 Post subject: Re: Brake Question
PostPosted: Mon Nov 15, 2021 8:18 pm 

Joined: Wed Feb 08, 2006 10:56 am
Posts: 43
Location: Bonsal, NC
Hello Eric,

Could be a number of things. I would check the packing cup on your brake cylinder, it may need to be replaced. Also check the fittings on the line from the pipe bracket to the brake cylinder for leaks and repair if needed. Does the same thing happen if you put it in emergency? If not I would suspect the service valve.

Also, while it may not be historically accurate, you may want to consider replacing the AB valves with ABD/W for operations, as the newer ABD/W valves are still widely supported by the industry.

Good luck!
Mike
New Hope Valley


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 Post subject: Re: Brake Question
PostPosted: Tue Nov 16, 2021 5:55 am 

Joined: Thu Oct 08, 2015 11:54 am
Posts: 1773
Location: New Franklin, OH
Thanks Mike. I’ll have them dump the air on the caboose and see if it leaks off.

Updating the valves has been tickling the back of my mind specifically for availability but that brings up another question. Is the mounting bracket with the pipe connections the same for ABDW and AB for an easy swap-out or is that going to require a bit of plumbing adjustments to fit a new bracket?

I’m educating myself as I go along to hopefully avoid some of those “uh-oh…” moments that turn a two hour job into a two month job.

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Eric Schlentner
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 Post subject: Re: Brake Question
PostPosted: Tue Nov 16, 2021 9:50 am 

Joined: Fri Mar 04, 2005 5:29 pm
Posts: 278
Location: Three Bridges NJ
Eric,

Mike put you in the ballpark as what to check for. You could also get a solution of soap and water and check the connections from the pipe bracket to the brake cylinder.

As far as the AB to ABD/W conversion, its just a matter of changing the top stud on the pipe bracket where the service portion mounts. It is shorter on the ABD/W and that's it.

Mulit-Service Supply in still services AB portions. Although, new AB cores have not been made in many years and refurbishing them time after time you might get a refurbished one that might not have much life left in it.

However, I have found that the AB portions to be very reliably. I just moved five vintage freight cars from a storage track a couple of miles away that had been sitting for probably three years. I brought a spare set of AB valves just in case, didn't need them.

Also, a good reference document to have is AAR S-486 https://aar.com/standards/pdfs/S-486.20180820.pdf

Scott


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 Post subject: Re: Brake Question
PostPosted: Tue Nov 16, 2021 12:32 pm 

Joined: Wed Sep 15, 2004 8:16 pm
Posts: 42
Eric,

What others have already said is good information.

One other thing that I would add is that you might - either by ear or soap suds - determine whether the release of air is coming direct from the brake cylinder or related piping, or whether the release of air is coming from the brake cylinder exhaust piping that leads to the atmosphere from the control valve pipe bracket.

If the former, this likely indicates an issue with the brake cylinder packing cup or associated components and piping.

If the latter, this likely indicates an issue with the control valve or related piping, being as the control valve itself is going into release position, versus the brake cylinder pressure simply bleeding off. If a car were equipped with an ABD or other more modern AB variant, a valve release would likely increase brake pipe pressure throughout the train, as ABD and more modern valves dump unused emergency reservoir air back into brake pipe upon release to effect a more prompt and positive release and recharge of the brake pipe and reservoirs on a long train - essentially the key function that makes it a no-no to bottle air on modern freight equipment.

Erich Armpriester
Strasburg Rail Road Mechanical Services


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 Post subject: Re: Brake Question
PostPosted: Fri Nov 19, 2021 9:07 pm 
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Joined: Sat Aug 28, 2004 1:15 pm
Posts: 1466
Location: Henderson Nevada
Is it bleeding off through the retainer (aka via the exhaust) ? Is so the automatic brake valve is releasing... for one of several reasons...

If not through the retainer, look to the cylinder packing...

Back to through the exhaust port/retainer... AB valves are sensitive to air pressure waves in short trains... and not a brake issue... just a system issue... or the service portion could be bad... Last time I checked Wabtec would service and test a ABD or later for about $130. for ABD or later... if true AB (early AB) look to Multi Service or Pittsburg Air Brake for clean and test..

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 Post subject: Re: Brake Question
PostPosted: Fri Nov 19, 2021 11:17 pm 

Joined: Thu Oct 08, 2015 11:54 am
Posts: 1773
Location: New Franklin, OH
Thanks for the suggestions. I’m heading to the yard in the morning so we’ll pump it up and dump the air to see if it bleeds off. On a 20 lb. reduction, it’ll bleed off in about 10 minutes.
The retainer is tight but…. We can’t hear any leaks anywhere so we’ll soap all the connections and joints. They found that one of the conductor’s dump valves did seep a tiny bit but that’s connected directly to the train line and wouldn’t affect the set.

We do own a single car test device stored and maintained at PABCO. We have a few more cars to go over with minor brake work over the winter down time so when we’re ready, we’ll have it shipped out or pick it up and test them all in one shot. I’m gonna have to get myself some more education.

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 Post subject: Re: Brake Question
PostPosted: Mon Nov 22, 2021 10:23 pm 

Joined: Wed Sep 15, 2004 8:16 pm
Posts: 42
Eric,

While not textbook perfection, the duration of 10 minutes for a 20psi reduction to bleed off to a release doesn't sound like a terrible issue. Theoretically, with an 8" piston travel this amount of BP reduction should create about 50psi in the brake cylinder, therefore suggesting that you have about 5psi of brake cylinder leakage per minute (assuming the leak is slow and steady, and coming directly from the cylinder or related piping).

The brake cylinder and retaining valve leakage test in the January 1956 single car test code allowed you a maximum of 5psi brake cylinder leakage per minute for "out of date" (newly repaired) cars, and 8psi brake cylinder leakage per minute for "in date" (actively in service) cars.

The same test in the April 1987 single car test code (the last test code to cover brass piston and ring AB) is even simpler, and only requires a set to remain applied for 3 minutes.

Given the seemingly minor nature/rate of your leak, a few minutes with some soap suds and a brief repair may get you back to "factory settings".

-Erich Armpriester


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 Post subject: Re: Brake Question
PostPosted: Tue Nov 23, 2021 6:59 pm 

Joined: Thu Oct 08, 2015 11:54 am
Posts: 1773
Location: New Franklin, OH
Erich - Good point.

After we put the 471 to bed for the winter, we’ll use our little 8-ton Plymouth to pull the caboose for occasional rides (no Santa trains this year). Our line has a slight down grade east to west so it’s a little unnerving when you don’t expect it and the brakes release on the caboose when standing. So far, I’ve found that the retainer does leak - but intermittently. So that’s one thing. We did an emergency set and it didn’t leak off. Then we did a service application with the same result. Go figure. I didn’t have enough time last Saturday to really dig into it further. I’ll take a more devoted whack at it on the 4th when I have a lot more time. We’ll service the cylinder if we have everything handy and cap the retainer pipe and see what happens.

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 Post subject: Re: Brake Question
PostPosted: Tue Nov 23, 2021 7:15 pm 

Joined: Fri Dec 18, 2015 8:30 pm
Posts: 77
jayrod wrote:
Erich - Good point.

We’ll service the cylinder if we have everything handy and cap the retainer pipe and see what happens.


I don't think that capping off the retainer pipe is what you want to do. The brake valve exhausts the air in the cylinder through the retainer pipe. Once air is in the cylinder, there's no way to release the pressure when the train line is re-charged. Capping it off would be alright to check for leaks around the cylinder and the pipes, but you would have to back the cap off slowly to get the brakes to release. Maybe swap out the retainer valve with a known good one and get that one a COT. Good Luck!


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 Post subject: Re: Brake Question
PostPosted: Tue Nov 23, 2021 7:38 pm 

Joined: Thu Oct 08, 2015 11:54 am
Posts: 1773
Location: New Franklin, OH
Ed - yeah, I wasn’t clear on that. I wanted to cap it to see if the cylinder leaks off since the retainer is intermittent. If we have the correct cup and whatnot, we’ll change it out along with the retainer and not bother to cap it for testing. I’ll paw through the parts bins to see if we have another of the same style of retainer for an easy swap. Still haven’t ruled out the service portion yet. We’re working our way towards it.

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Last edited by jayrod on Tue Nov 23, 2021 7:40 pm, edited 1 time in total.

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 Post subject: Re: Brake Question
PostPosted: Tue Nov 23, 2021 7:40 pm 

Joined: Thu Sep 22, 2011 4:29 pm
Posts: 1899
Location: Youngstown, OH
Why would a caboose even have a retainer? Our Erie caboose doesn't have one and the P&LE cabs have whistles bolted to the pipe bracket so that it sounds off when the brakes release.

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 Post subject: Re: Brake Question
PostPosted: Tue Nov 23, 2021 7:42 pm 

Joined: Thu Oct 08, 2015 11:54 am
Posts: 1773
Location: New Franklin, OH
Don’t know if it’s weird or not, but it has one. Mounted high on the outside end wall.

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 Post subject: Re: Brake Question
PostPosted: Tue Nov 23, 2021 9:27 pm 

Joined: Thu Aug 05, 2010 2:06 am
Posts: 329
I can say the DM&IR caboose C-74 at Mid-Continent Rwy has a retainer........mld


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 Post subject: Re: Brake Question
PostPosted: Sat Nov 27, 2021 9:19 am 

Joined: Thu Sep 22, 2011 4:29 pm
Posts: 1899
Location: Youngstown, OH
If you would like to upgrade to ABDW brakes on that car, I have a set of control valves off of a CSX boxcar that I would give you. Emergency portion is good. Service portion doesn't release so it would be good as a core for unit exchange.


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