John:
In 1960 th UP took delivery of both GP 20s and SD 24s. These were our first experience with the 26L. It is my understanding that the biggest advantage to this valve is that it can be overhauled with a "kit" by a parts replacer rather than a machinist hand lapping metal parts to the correct fit. I personally loved the 24RL. It has the self lapping independent with the down bail just like 26L but the automatic quadrant is just like 6ET except that it doesn't have the "hold" position. I preferred this as I never liked the fact that the 26L has such a harsh initial application like 6 psi minimum. There are times when a 3 lb set can do wonders in train handling so long as you are going to stop and can then make a heavy reduction to assure a good release. The late UP Steam power had (has) 8 ET. It is like 24RL except with an independent like 6ET. Both 8ET and 24RL have pressure maintaining features with a cut out cock for checking brake pipe leakage during the air test.
One of the threads here mentions bridging the brake valve. This, of course, was strictly against the rules but some hoggers did it. The big danger here is that you accidently "bridge too far into release and kick off the brakes. The "feed valve" method made more sense if you didn't mind standing on your head. With this you backed off of the feed valve setting a ways and let the leakage make your initial set. If you need more, you just reduced more. But like bridging, if you went too far, you couldn't come back for fear of releasing everything. It was verbotten by the rules also but at least you had an air gauge to guide you. It just goes to show what a wonderful thing pressure maintaining features really are especially with long trains at higher speeds.
Les Clark
