It was comforting to read the mention of the rule relating to the precautions
that MUST be taken BEFORE a person goes between cars or performs a work related
activity on the end of a piece of rolling stock. Over the years many an
employee has been injured or killed because a piece of equipment moved
unexpectedly ------------- regardless of the reason.
Retainers: Since it is a fact of air brake design that pressurized air entering
the brake cylinder causes the brakes to APPLY it stands to reason that if
braking effort is to be maintained this pressurized air must be RETAINED within
the cylinder. The simplest method of achieving this is to not release the
brakes on the train. It is also a fact of brake design that, as long as the air
remains "set", the trainline cannot be recharged**. The safest method utilizes
the RETAINING VALVE. The retainer is a devise that allows the trainline to be
recharged because it RETAINS some of the pressurized air within the cylinder.
During a release of the brakes this pressure would normally vent directly to
the atmosphere . As mentioned by John Knopp the Engineer may need to release
the air in order to have a good charge in the trainline for the next steep,
descending grade but, since his train is still on a downgrade, the release of
the brakes would probably result in an overspeed condition (over the max.
authorized speed). If the grade conditions require the use of retainers
specific formulae are used to determine the total number of retainers that must
be set ("turned up"). On a 1% grade the maximum allowable tons per retainer is
250. On a 3% grade the max. allowable tons drops to 70.
Current RR practice only allows the use of the "HP" (no,not a printer) or HIGH
PRESSURE position when setting retainers. With the handle in the 45 degree
below horiz. position the valve will retain 20 psi. in the cylinder. Other
positions include EX, Direct Exhaust (full release, handle up) SD, Slow Direct
(handle 45 deg. above horiz.) which produces a blowdown time of approx. 86 sec.
and LP, Low Press. (handle horiz.) which retains 10 psi. in the cylinder.
**The new Electronically Controlled Brakes have a feature that allows trainline
charging while a brake application is in effect.
If someone hasn't done it before I get time to write again I'll hit on the
control (triple) valve for the next discussion.
Later
Karl
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