Some responses for additional comment
1. On a non-maintaining brake valve, how much does brake pipe leakage affect your "set" on a long grade? I would think that gradually the application would increase depending on the rate of leakage. Say you draw off 10# and leakage is 1 PSI/min., 5 minutes later you'd have around a 15# set. Sounds like a problem unless you open the throttle and drag the train down the hill (power braking).
Leakage effects operation.
Except, that in heavy grade territory, if you have to get rid of the air for some reason, there generally isn't enough recharge time before you have to go into them again. And deeper than the first set if the recharge wasn't completed. Retainers are there for a reason.
When I worked for the Grande, I recollect that power braking was not done on freights in mountain grade territory. Too hard to keep them under control. use air & dynamic only.
Power braking can be difficult without an almost zero leakage train line and or the pressure maintaining feature. Especially when long down hill moves are being made.
With the older wood equipment, the ends came out of cars on occasion, especially when diesels first arrived on the property, some the old heads had difficulty understanding the use of the load meter and the power available at the rail. But this also occured when trying to power brake.
So power braking with steam or diesel could be looked for shorter tains in 'roller coaster' teritory, but not on heavy grade. It should be well thought out before doing it and, if your not sure, take the safe course and don't do it. And, always have a back up plan (or method) for handling any train.
Whether your hauling people or freight, this isn't play time.
Power braking can be a nice 'tool' to use, but there are limits:
Knowing train length & weight, load/mty make up, available power, grades, curves (heavy curves give additional brake effort but can cause string-lining if too much power is used), rail condition, brake shoe materials of cast iron Vs composition shoes (can give different handling charateristics), etc, etc.
Also, since brakes (just using the automatic air) - set and release from front to rear, the release of a long train at too slow a speed can cause a break in two if the head end is not controlled and runs out.
I wonder what some of the old heads thought the 1st time they had one of those 70 plus car freights eastbound from Cumbres to Ala? Wonder if the rear end crew made out?
One of the better features or additons including the maintaining feature is the air flow meter. For those that don't know, this indicates the air flow from the brake valve into the train line and this gives you an very good indication of the recharging condition of the auxiliary reservoirs. On longer trains, just because the brake pipe pressure to have arrived at the prescribed pressure, doesn't mean that the aux reservoirs are completely charged.
With 6ET or the old A-1 equipment, how many of you in a recharging situation, have momentarily moved the brake valve from running to lap, looked at the brake pipe gauge to see the rate of pressure drop compared to the initial terminal leakage test, and then moved the handle back to running position to complete the recharge? If there was a drop, that wasn't just leakage, it was that the aux reservoirs taking air from the train line. So the gauge 'drop' included recharging plus the leakage.
One of the biggest problems with the K and P brakes? No emergency reservoir. The greatest brake pressure you can obtain is when the system is completely charged and the 1st set is made.
The #6 automatic brake valve had a holding position also.
Also consider the other generalities - whether to use the bunch train or stretch train braking methods? And that doesn't include power braking.
There is so much that could be added to this, but enough already!
2. If that's the case, do you wait for the speed to drop sufficiently to allow you to release the brakes, recharge the train, and repeat the process? (What I've called "cycle braking") Clearly, on a heavy grade, retainers make this much easier by retaining brake cylinder pressure.
True. But while I am familiar with this and the operating procedure, I have never had to use this method. Others out there will have had more actual experience with this than myself and should be able to comment on it.
3. Dare we get into the difference between freight air and passenger air?
Maybe someone else wants to dive into this discussion.
Chris
