Standards and common practices

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vanisaac
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Standards and common practices

Post by vanisaac » Sat May 27, 2017 2:36 pm

The IBLS wiki contains a wonderful number of standards for the home hobbyist to integrate into their designs in order to properly interchange with other equipment - tire gauges and machining profiles, coupler placement, track standards. However, there are some areas of common interchange where the fledgling hobbyist is at a significant disadvantage when trying to design their equipment, namely brake lines and bolster center plates. Does anyone have some 1.5" / 1.6" scale standards, or at least common practices when it comes to the following:
  1. What type and size of connector (tube and coupling hardware) is used to couple positive pressure air brakes between cars?
  2. What PSI air pressure is most commonly used for fully engaging positive pressure brakes?
  3. What size of center plate is most common between railcar bodies and trucks, and is there a standard profile/machining?
  4. What sized center plate pin is used?
Van Anderson
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Fred_V
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Re: Standards and common practices

Post by Fred_V » Sun May 28, 2017 7:45 am

The most irritating thing for me is couplers from different suppliers that won't fit each other.

There are some glad hands available for brake lines and you can make your own. Some use fittings from Clippard. I've seen mostly about 80# pressure as adequate for brake systems. I know this is going to open a huge can of worms as everyone on the planet has their own idea as to what should be done.
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vanisaac
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Re: Standards and common practices

Post by vanisaac » Tue May 30, 2017 10:45 pm

Thanks for your help, Fred. I will be building my brake system and measuring the force necessary for braking before purchasing the piston and the rest of the pneumatics, so that 80 PSI figure gives me the math I need to size things.
Van Anderson
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ccvstmr
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Re: Standards and common practices

Post by ccvstmr » Wed May 31, 2017 6:12 am

vanisacc...about the only thing you can be sure of once you get beyond the track 'n wheel standards is...there's nothing you can be sure of! There comes a point after your equipment can roll down any track (barring 7.25" vs 7.5" for the 1.5" or 2.5" narrow gauge tracks)...where things are pretty much left to the supplier or builder.

What type and size of connector (tube and coupling hardware) is used to couple positive pressure air brakes between cars?
- many people use 1/4" OD x 1/8" ID poly tubing between cars. Can be used on/under the car as well. Some people use copper tubing.
What PSI air pressure is most commonly used for fully engaging positive pressure brakes?
- my max pressure for a regulated brake pipe is approx 60 psi. Normal brake applications (for straight air brake system) are usually between 10 to 40 psi. Only on rare occasions is full pressure necessary. A remote brake system in a caboose for on/off control (to keep the rear end of the train from rolling away on grade) is in the 50 psi range.
What size of center plate is most common between railcar bodies and trucks, and is there a standard profile/machining?
- best response to this is...depends on the trucks. I've found a 2" x 7"/7.5" x 1/4 or 5/16" plate works fine for most trucks. But then, I've got Bee, Mercer, Harpur, Winton, Cannonball and a few non-descrip trucks under my rolling stock. The biggest problem is not all truck have the same rail head to top-of-truck bolster distance. The plate size described spans the side sway pads on the trucks while allowing the truck to swivel...and NOT hang up on brake hangers. On most of my equipment, the truck center and side sway pad are machined to the same plane. I use a 1/32" Teflon washer between the truck/car body centers for swivel AND to provide a 1/32" gap between center plates and truck side sway pads.
What sized center plate pin is used?
- I've used 3/8" hex head bolts for years...but am slowly upgrading to 1/2" bolts. The threaded end of the bolt is screwed into a drilled/tapped center sill and secured with a jam nut (usually there's a hole in the floor board to access the jam nut if necessary...which gets covered over). The center pin is left long to clear the underside of the truck bolster. A cross hole is drilled in the center pin for an "R" clip or hairpin clip. Usually have a large fender washer between the clip and the underside of the bolster. This keep the truck with the car when re-railing. This beats bolts screwed in from the underside of the car. Gravity is tough to beat! These kings pins have never failed. To service the truck, pull the pin, lift the car end until the king pin clears the truck and roll the truck out. Made it a practice to use Clippard MQC quick connect fittings to hook the brake pipe line to each of the trucks with brakes.

Make sense? Carl B.
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Harlock
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Re: Standards and common practices

Post by Harlock » Wed May 31, 2017 11:09 am

The truck bolster questions are part and parcel to the type of truck you are using, and don't relate to interchangeability of coupled cars. A standard wouldn't make much sense in a world with many radically different truck types and scales. As long as your coupler center height ends up where it should be, it's all good. Recommended practices for interfacing trucks with cars is a good idea to share though.

No one ever standardized on air connections, probably because few people had working air brakes back in the day beyond tender brakes, and by the time people started implementing train brakes more frequently, it was too late. Live Steamers here tend to be radical individualists.

Some countries with cohesive umbrella organizations over their clubs have done it - New Zealand has standardized their club vacuum brake connections except for one or two clubs. The clubs there are very focused on giving public rides and almost no one has their own rolling stock due to the economics of transport and storage over there, so it makes sense since all ride cars are shared and there are almost no scale model cars.

Air pressure: For the weights and cylinder sizes on my train, I use 65lbs max. For normal braking on 1 - 2% grades I find I am using about 10 - 18lbs of air. For a fast stop without sliding I apply full pressure. Depending on the weight of your cars and bore of your airbrake cylinders, this may vary widely.

I use clippard shutoff disconnects with 1/8" lines. They do not pull apart on their own, but I am using safety chains that are shorter than the lines, so I am not worried about damage. The great part about these is that they do not leak. I'll often leave the air in the reservoir in the boxcar between meets, come back a month or two later and find the pressure is still almost full. parts list: http://www.chaski.org/homemachinist/vie ... 60#p284360

I also now use those same disconnects for each truck, so I can detach the trucks and remove them from the car without cutting the lines.

Best,

-Mike
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John_S
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Re: Standards and common practices

Post by John_S » Wed May 31, 2017 7:16 pm

Myself and quite a few others in the CSPPRY use Tom Bee brakes on our rolling stock. His system uses 1/4" poly tube between cars with Schrader valves on the end sills. These are positive pressure brakes. Application pressure really depends on the weight of the car and trucks; I have three pieces of rolling stock that have brakes: the tender for my locomotive which is scratch-built prototypical brakes, a boxcar with Tom Bee brakes, and a gondola with Tom Bee brakes. I use 40lbs of pressure for full application.

If you have a lightweight car you may need to regulate the pressure down a bit to keep from locking up the wheels.

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Bill Shields
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Re: Standards and common practices

Post by Bill Shields » Thu Jun 01, 2017 7:06 pm

If you have a lightweight car you may need to regulate the pressure down a bit to keep from locking up the wheels.

Just like the 56.5" railroads (giggle....)
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johnpenn74
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Re: Standards and common practices

Post by johnpenn74 » Fri Jun 02, 2017 9:01 pm

How much braking force:
Wait a sec.... Brakes on an empty car should be on the edge of locking up at FULL application or emergency. This way all cars brake with the same behavior regardless of their empty or loaded weight. I think that is how the prototype does it. That being said, brake size (cylinders) and linkages should be calculated and sized for a car of a specific empty weight. Also, brake shoe to wheel material makes a difference and has to be in the calculations since friction coeffs for wheel to rail and wheel to brake shoe vary.

Air pressure:
Trainman once told me 75 for freight and 90 for passenger. Makes sense. Someone else told me it killed their pump to keep it up that high. I know several people that use 60 in Ohio.

I have been working on my log cars, calculating the weight to friction to force to PSI relationship. Easy enough once you set it up in excell.

Hose location :
Another thing one might consider is hose location. Since most people have straight, a few have vacuum and some even have automatic. Lets start mounting the car air hoses on the correct side of the coupler based on which system you have.
Facing the coupler:
- Automatic on right, straight on left.. no idea which side the vacuum line was one (if it was even on the cars, maybe it was only on engines?)
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vanisaac
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Re: Standards and common practices

Post by vanisaac » Sun Jun 04, 2017 5:15 pm

So John, the way I am doing this is I am building my car with the braking system all set, but using a hand brake, and not installing pneumatics until later (mostly for cost reasons). So my plan was to measure the force required to stop the car with the hand brake, and then size my piston by that calculation. But I can't measure that force without riding the car. So should I be able to do a simple weight conversion - (empty car weight / full car weight) x full car braking force = empty car braking force - or is there some other way I need to figure out the braking power needed in order to size my piston?
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Greg_Lewis
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Re: Standards and common practices

Post by Greg_Lewis » Mon Jun 05, 2017 10:43 am

Clippard makes a small pressure regulator that could be used to control the pressure to a car cylinder. Thus you could adjust via trial and error, which might be better than figuring out friction and leverage factors. And if you wanted to get fancy you could use two with a swtich and have one set for empty and one for loaded.
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Re: Standards and common practices

Post by BigDumbDinosaur » Mon Jun 05, 2017 2:01 pm

Greg_Lewis wrote:Clippard makes a small pressure regulator that could be used to control the pressure to a car cylinder. Thus you could adjust via trial and error, which might be better than figuring out friction and leverage factors. And if you wanted to get fancy you could use two with a swtich and have one set for empty and one for loaded.
Another way to decrease the likelihood of sliding wheels on light cars is to have an equalizing reservoir as part of a straight air brake system.

The output from the brake valve is piped to the equalizing reservoir and the reservoir, in turn, is connected to the brake pipe. When the brakes are applied, the equalizing reservoir must be charged before the brake pipe will be pressurized. As that takes a certain amount of time, rapid changes in brake pipe pressure cannot occur, producing a smooth brake application, no matter how abruptly the engineer moves the brake valve. A smooth application is less likely to cause immediate lockup.

I did this with my F-unit and achieved brake operation that is very smooth and predictable. The reservoir is mounted on the forward end of the control car and is built into two unequally-sized sections: the larger one a reserve air supply that is pressurized through a check valve from the main reservoir on the locomotive, and the other section being the equalizing reservoir. The reserve supply stores enough air to make two full brake applications, even if the locomotive's air compressor goes kaput, a major leak develops in the locomotive's compressed air plumbing and the compressor can't maintain pressure, or the main reservoir hose between the locomotive and the control car bursts.

As a bonus with this setup, the air discharge that occurs when the brakes are released makes a more realistic sound than would be heard from the brake pipe discharge alone. :D

The one negative is that more air will be used per brake application/release cycle, as each application has to charge the equalizing reservoir, as well as the brake pipe. Obviously, when the brakes are released that reservoir charge will be lost.
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