Thanks for the info. We're scrounging for a manual tester or may build our own.

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.

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.

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.

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.

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.

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.

Circling back here on the subject of orifices for the HRA device as we finally found some time to confirm things in greater detail. Data for orifices used in SRC's device as shown in the attached screenshot.

No change was made to the entrance or exit features of the McMaster orifices, nor of the resulting orifice length. Using the "alternate" method of testing the device, all tested orifices charged and exhausted air from the 800 cu. in. volume reservoir within the prescribed limits.

Perhaps if we can ever open up RP-002 for some edits we'll add some data for suggested hardware. For now, hopefully this may be of some help for anyone looking to construct the device.

- Erich Armpriester
Strasburg Rail Road Mechanical Services

Erich, thanks so much for posting that additional documentation! This confirms that the devices used as orifices were actually designed as such, and not just hex socket pipe plugs drilled out haphazardly. I agree that the list of McMaster part numbers, or the actual manufacturer's part numbers, "or equivalent", would be a good addition to the Recommended Practice. This would ensure that people fabricating the device according to the plans will wind up with something that passes the self-test.