NW-Mailing-List Digest, Vol 62, Issue 3

[NW Mailing List]

Hey, I actually learned something from the air brake portion of 
mechanical in my engineer training! :)

You're right, to an extent, but there's more to it.  If you have a 
reservoir as big as Texas (at 90 psi) and a normal sized brake cylinder 
(at 0 psi), the two will equalize pretty darn close to 90 psi.  If you 
have a reservoir and a brake cylinder of exactly the same volume, the 
two will equalize at 45 psi.  The larger the reservoir, the higher the 
final pressure in the brake cylinder.

Thus, both reservoirs actually DO supply air at the same time, because 
both are trying to equalize with the lower pressure of the brake 
cylinder, and of course with each other when all three are connected by 
an emergency application.

To take it a step further (Jimmy, you probably already know this, but 
others might not)..  If I make a service reduction, the aux. res. and 
brake cylinder will equalize at some pressure, say around 50 psi.  If I 
then make an emergency application, the emergency reservoir pressure is 
higher than either the aux. res. or brake cylinder, and it will then 
cause the system to equalize at a higher pressure, closer to 70 psi.

Physics is never basic. :)
Ken Rickman

NW Mailing List wrote:

>     Like I said, being as both cylinders have the same pressure, they 

> cannot supply air to the brake cylinder at the same time. You can have a 

> reservoir as big as Texas , but it still only has the same amount of 

> pressure in it that the aux. res. has. Basic physics.

-- 
Kenneth Rickman - krickman1 at carolina.rr.com
Salisbury, NC