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 Post subject: Re: Single car air brake tester
PostPosted: Wed Sep 11, 2024 6:06 pm 

Joined: Thu Oct 08, 2015 11:54 am
Posts: 1848
Location: New Franklin, OH
Thanks for the info. We're scrounging for a manual tester or may build our own.

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 Post subject: Re: Single car air brake tester
PostPosted: Thu Sep 12, 2024 3:01 am 

Joined: Wed Oct 13, 2004 12:56 am
Posts: 487
Location: Northern California
I agree with Jeff about an orifice. They are so touchy that I would avoid a square corner orifice. If a square corner orifice was used, the faces should be ground and the hole drilled then reamed. But even that is not good enough. The length of clear straight pipe on both the input and discharge can impact the results.

I worked on some HVAC testing at ETL years ago. Part of the test was measuring air flow through a orifice. If a person walked across the discharge stream with in 20 feet of the orifice it would change the results.

The HRA committee needs to revise their recommend practice and provide appropriate data on the design of the orifice.


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 Post subject: Re: Single car air brake tester
PostPosted: Fri Sep 13, 2024 12:13 am 

Joined: Fri Mar 14, 2014 11:44 pm
Posts: 207
Erich Armpriester wrote:
Eric,


On the chokes/orifices, so long as the HRA device is plumbed together such that it meets overall form and volume requirements, there is no specification on orifice form other than diameter. See Figure 3 of RP-002 for construction details. So long as the device is air tight, and charges and exhausts air at the proper rates from a fixed volume as called out in the test code, it will perform its function properly - just the same as OEM manual devices are tested for proper function. This allows a railroad some flexibility (within limits) to use equipment and tooling that is available to them to construct the device.

-Erich Armpriester


I agree that if the constructed device has the same charge/discharge times when self-tested, it will properly conduct the actual test on the single car.

There should be some guidance given on the construction of the orifice, e.g. a recommended supplier, or a more specific procedure for constructing it other than just the diameter. Without that, people may construct the device as specified, and have it fail the self-test, with no further guidance on how to get it into compliance.


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 Post subject: Re: Single car air brake tester
PostPosted: Fri Sep 13, 2024 10:28 am 

Joined: Thu Oct 08, 2015 11:54 am
Posts: 1848
Location: New Franklin, OH
That's pretty much my prime question. I know the diameter, length and shape of the orifice affect the air flow. Diameter we know but what of the other two? Or does it not matter that much considering the pressures and orifice sizes we're working with here? All the other parts are basically hardware store type items. To me, the orifices are the sticking point to building your own.

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 Post subject: Re: Single car air brake tester
PostPosted: Thu Sep 26, 2024 9:52 pm 
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Joined: Thu Nov 12, 2020 1:04 pm
Posts: 6
Location: Rochester, NY
Jeff H,

I purchased Hex Pipe Plugs from McMaster-Carr and drilled the proper diameters specified in the HRA spec. For the two smallest holes, I pre-drilled with a larger bit to remove the majority of material and then finish drilled with the specified bit for the last 0.100" of material. I tried my best not to break any of those really small diameter bits.

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 Post subject: Re: Single car air brake tester
PostPosted: Thu Sep 26, 2024 11:15 pm 

Joined: Thu Oct 08, 2015 11:54 am
Posts: 1848
Location: New Franklin, OH
Looks like we're going to go a different route. We're off the hook for doing a DIY freight brake tester or begging/borrowing one, I hope. We've gotten lucky and it appears we're having an older automatic tester donated to us. I guess we'll find out how well that works for us. With the railroads using the new four port testers, it may be advantageous for you to ask around and see what pops up out of the far corner in the back room of someone's car shop. Shops will sometimes hang onto to stuff for "just in case". It never hurts to ask.

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 Post subject: Re: Single car air brake tester
PostPosted: Fri Sep 27, 2024 11:40 pm 

Joined: Fri Mar 14, 2014 11:44 pm
Posts: 207
Justino99 wrote:
Jeff H,

I purchased Hex Pipe Plugs from McMaster-Carr and drilled the proper diameters specified in the HRA spec. For the two smallest holes, I pre-drilled with a larger bit to remove the majority of material and then finish drilled with the specified bit for the last 0.100" of material. I tried my best not to break any of those really small diameter bits.


Thanks for the info!

How did you install the chokes inline with cocks 1 and 2 and still have enough thread for the nipples?

I've made chokes out of hex plugs in almost the same way. It's possible that the pre-drilling with the larger bit is accomplishing the gradual entrance region. I take it your device passed the self-test within the required charging and discharging parameters?

The HRA pipe fitting test device is using these individual valves and chokes in place of the "A valve" rotary valve. Much easier to keep air-tight than the rotary valve.


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