Well, back in the steam days that is how you dropped a train down a long grade.

Long story short, you start down a grade and make a set. It holds the speed in check but starts to slow way down. You kick the brakes off and pretty soon here comes the speed. You go after them again and again finally slow down too much and you kick them off. This time when the speed gets you going again you make another set. Trouble is you have not charged up the brake pipe from your first set. You have maybe 50 lbs in the caboose and the brakes are released. This time you come to a stop, send the brakeman back to tie brakes and start charging up the brake pipe.

With a retaining valve, the brake cylinder pressure is held, on that car, while the brake pipe is recharged. In effect it holds some of the cars set up, while the others release and recharge. Rule 17 on the SP stated, "If at anytime in Engineer's judgement use of retaining valves is required, stop will be made and retaining valves will turned up in accordance with his request."

Back in the day, most of the "Pops" were near the top of a car if it had a high brake. Easy for the brakeman to walk the top of the cars and set them up or knock them down. When you did use retainers you had instructions where and how long you had to stop to cool the wheels back down. Each division had special instructions of how many pops would be used, where and what tonnage per car.

With the diesels you now had dynamic brakes. That gave you more control on the balance of the air and the speed and how you could recharge your brake pipe.

There were a lot of tricks you could use to try not to set the pops unless you had to. It took a long time to set them up and then knock them back down. An easy hour or more. You could "Ping-Pong" the brake valve and get a couple of brakes hung up back in the train.

In the steam days with the old brake valves you could "Bridge It" setting the brake valve on just the edge of release.

There was always "Feed Valving It" that was very much against the rules. I only had to set some pops once, trying to get down Cuesta. I was a young runner and had a by-pass lumber train going east out of Wat.Jct.. It was heavy for the Coast around 8,000 tons. Well, I made my set coming out of Tunnel 6 and everything was going okay. Then we started to bog down. Thinking my dynamics were okay and had a helper back there, I kicked them off. Before I knew it I was up to 35 at the east end of Serrano before the air checked and started to bring the speed down. I came to a stop almost at Tunnel 11. Now what. I had never used retainers before. The head man told me to leave the air set and called the conductor on the radio. Told him he was going back to check on a possible stuck brake. He went back and set up 12 pops. Came back up and told me to kick em off. I was able to make it the rest of the way down to Hathaway on one set. As a young runner you don't want to "Baby Food It" but there is a time when you need some help. Retaining valves were just that. Out of 8 units, only had one dynamic brake working. The helper lost everything when he started down the hill.

The other heavy trains were the beets but that was something all by itself. You made a set with them and you just never released them, pulling on them if you had to. Their brakes were so bad, pops wouldn't help you.

Only one other time and that I sued them was on the Siskiyou line. We lost all DB on the head end and helpers. "E" ticket ride until we got stopped for the first time.

Nudge