Greetings:
When Steamtown was still at Bellows Falls, VT, our air brake man was John Eames, retired from the Maine Central. John had been a valve setter at Waterville, but when MEC dieselized, he went into the airbrake shop.
John always used "air brake hones" made by Carborundum Co. for the seats. The hones were made in a variety of sizes to fit all airbrake valves. They also made "bricks" to grind the slide valves on. The hones and bricks themselves are flattened on a cast iron surface plate, which as noted above are incredibly cheap. Aluminum oxide powder is used as a grinding medium on the plate as it is much easier to work with than Clover compound. Clover compound is used for lapping the slide to the seat.
John taught me to use these methods and I bought a set of hones for myself.
When I went to the Valley Railroad in 1986, they were having horrendous airbrake issues, so we sent pickup truck loads of valves up to John, who had a small (but well equipped) shop in his basement. Wayne Hebert (now the Shop Supervisor at VRR) took many loads of valves up and worked with John for days at a time, learning John's methods.
When we have the time, we still clean and repair our own valves, but occasionally we send them out for cleaning. Usually, we can send a valve out twice before it needs to be honed again.
If we have a triple valve that won't pass a single car test after we have worked on it, it is sent to Strasburg, who, as noted above, has a 3T rack (and folks that know how to use it!)
Be well,
J.David

A big THANK YOU for the many responses and advice!
Of course, don't let that stop other responses. This knowledge base is what make the forum great.

-Clyde Putman
Friends of the Cumbres and Toltec Scenic Railroad

With the hope that it is of some help, I can share a few thoughts regarding my experiences lapping valves through my years in Strasburg's air shop.

We have an inventory of various lapping blocks/sticks/plates that are a proper fit for the various valves we deal with. When it comes to lapping triple slides, these sticks are made from steel, about 10"- 12" long, have relief cuts in them similar to what was described in posts above, and are roughly 1" square in section (or, about .010 - .020 narrower than the sides of the slide valve seat to which the lap is to fit). We true these lapping blocks on our surface grinder as needed.

The general process is to use these lapping sticks and our lapping plate to take care of the vast majority of truing the seat of the bushing and the valve. Ideally, the valve and the bushing are only lapped together as the last step of the process, and then only very lightly with fine grit (800 or 1000) lapping compound. The theory is that the lapping sticks and plate will get the surfaces truly flat, and the last light lap or two between the valve and the seat simply serves to "kiss" these two together. Any more than a light lap will only serve to begin to replicate the wear that the valve and seat see in service, and here you can start chasing your tail in a hurry. Linn had a helpful suggestion recently in adding a few drops of (clean!) solvent to the fresh lapping compound at the start of the lap. This is something I had not tried until he suggested so, and, turning the lapping paste into more of a lapping oil, it seems to help free up the abrasive grains and allow the lapped surfaces to come into more intimate contact with each other.

For my eye, an extremely helpful check on the progression of the lapping progress and the condition of the seats is a dry lap. Clean the lapping stick (or slide valve, as the case may be) and the slide valve seat, and lightly lap the two together in their perfectly clean and dry state. The high spots will show a pronounced shine, and the low spots will still be dull from lapping. The valve and seat are flat when you have a reasonably even, continuous shine across the entire seat.

We recently had quite a fight with lapping in a slide valve and a rotary valve. I think where we went off the deep end at step one was that we were starting with flat laps that weren't flat, rather they were worn hollow from previous use. In initially using the laps in this condition, we made the seats worse before we made them better. The lesson learned here was to make absolutely certain that the lapping stick or plate is truly flat, and if there is any question, true as needed. We won the fight with these valves in the end, but had a long uphill battle to get there.

In my experience with lapping and maintaining brake valve slides, I've found two cliche phrases to hold true:

"Less is more." The less lapping you can do, the better. Don't be afraid to start off with a coarse grit to take care of the "heavy lifting". One or two laps with 200 grit is far better than lapping your brains out with 800 grit. This will save time and - as much as anything - help alleviate mental and physical fatigue during the lapping process.

"If it ain't broke, don't fix it." When I started my work in the air shop I inherited a fleet of valves that had their slides in excellent condition. Over the past 12+ years of my involvement in this work, we've seen the leakage in our slides creep up ever so slightly due to the inevitable wear seen with regular service. However, the vast majority are still in very good condition, still passing the "new and repaired" test limits with ease. A valve that is in good condition can easily be kept that way with regular, thorough cleanings and proper lubrication.

Lastly, as Kelly and J. David mentioned in earlier posts, SRC does have a 6ET test rack, feed valve test rack, and 3-T test rack, and we welcome contract repair work from those that don't have this equipment.

As time goes on and more and more historic equipment is ABD'd and 26L'd, it is nice to hear of those fellow operations that continue to hold true to preservation and keep these older braking systems - and related knowledge and skills - alive and well.

-Erich

Has anyone got a good photo of a 3t test rack they can post?

What's the dif between the 3t and the 6ET?

Thanks!

.

Make sure you keep your fingers away from the jaws of the clamps! I have been told that many of the air room guys from the triple valve era were missing the end portion of a finger because it was in the wrong place when the valve for the pneumatic jaws was operated.

The 3T must mean the rack will test three models of triple valves: K, L, & P.

Thanks for the photo and info.

Also the H valve, M and R triple valves according to the test code booklet from Westinghouse Air Brake

Found a couple of interesting items on the internet:

Google Books: Railway & Locomotive Engineering, November, 1917 issue
Introducing the 1917 "Improved No. 3 T Triple Valve Test Rack"

http://www.hawaiianrailway.org/maintenance/WestinghouseTripleValves.PDF

Nope. It is simply the 3rd generation of triple valve test rack. The #1 and #2 generations were
wooden workbenches with a very different layout. As I recall, the #3 rack introduced the
"finger buster" method of mounting the valve under test, also the universal adapter plates
so that #1, #2 and #3 size triple valves could be tested on the same rack. The "R" valve
which controls the piston stop and ring leakage tests may have also been introduced with
the #3T rack.

There were far more than 3 models of triple valve. This board is dominated by diseisel and
boiling-water traction types, but us juice jocks get to deal with more obscure valves. The M
was a very popular valve for short interurban-style trains. The R and variants saw a lot of
use on elevated rapid transit equipment. S & T were sometimes used on motor-trailers.
All of these can be tested on a 3-T rack.

Incidentally, I have modified my 3-T rack with a safety catch that makes it harder to accidentally
open the cock which admits air to the finger-buster jaws.

I will second JeffH's comment that the 3-T rack can test many more types than just K, L, and P triples. As he noted, those are simply the most common to us steam and diesel hauled railroaders. In addition to the other types already mentioned, the rack can also test numerous styles of obscure (these days) New York design valves, and the older plain-style triples.

As for the "finger buster" clamping jaws, as simple as it is, this is a bit of engineering at which I've always marveled; it's pretty darn slick. Through the process of mounting cumulative hundreds of valves to our rack, I've often thanked Westinghouse for incorporating this in the design. It sure beats the heck out of tightening and loosening three or four bolts every time a valve is cycled in and out of the rack. In addition, I can't say I've ever had an issue with the "finger buster" part. During the clamping process, one hand is operating the valve to admit air to the clamping cylinder, while the other is supporting the front end of the triple and holding it up and against the rack, well away from the clamping jaws.

-Erich