 |
Re: Auxiliary Braking, DPU is better
Author: SP5103
Date: 02-10-2019 - 15:39
>When stopped on a grade the locomotive independent brakes would be fully applied which cuts out the dynamic brake. This is why you "bail off" or actuate the locomotive brakes when setting train brakes (automatic brake) and you want to retain dynamic braking.
Not exactly.
When you apply the dynamic brakes, the Dynamic Brake Interlock will bail off the engine brakes. There are actually two standards, in one they truly do bail off the engine and the engine brakes will not apply, the other standard is if you get out of dynamics any automatic brake application will reapply on the engine unless you have manually bailed it off. BN may have had a third standard, limiting the dynamic braking effort to a minimum once brake cylinder pressure reached a certain pressure.
If the engine is equipped with extended range dynamics, there is a pressure switch that will cut out the extended range feature if brake cylinder pressure above a moderate amount. The only time you use the engine/independent brakes with dynamics is just before stopping to keep the slack from running out as the dynamics fade out to zero, otherwise both brakes can slide the engine wheels.
You can't use dynamic brakes to hold a train stopped on a grade - if the wheels aren't turning, the dynamic brake system isn't creating braking effort. I believe the independent/engine brakes generally can create about the same braking effort as the dynamic brakes, so adding dynamic brakes on top of the engine brakes for a stopped train does nothing, unless you are slowly releasing the engine brakes preparing to begin movement.
Not to confuse things, but most passenger engines now have "blended braking". When in effect, making a brake pipe reduction causes the engine dynamic brakes to automatically apply (assuming the throttle is in idle). In addition, the engine brakes are also applied by the system, from 10 psi or more depending on the brake pipe reduction, and the how much dynamic braking is being created in relation to speed. Properly functioning, the system balances the combined engine brake cylinder pressure and dynamic braking effort to a safe limit to keep the wheels from sliding. This is how the dynamic braking is usually controlled when a cab car is leading.
Not exactly.
When you apply the dynamic brakes, the Dynamic Brake Interlock will bail off the engine brakes. There are actually two standards, in one they truly do bail off the engine and the engine brakes will not apply, the other standard is if you get out of dynamics any automatic brake application will reapply on the engine unless you have manually bailed it off. BN may have had a third standard, limiting the dynamic braking effort to a minimum once brake cylinder pressure reached a certain pressure.
If the engine is equipped with extended range dynamics, there is a pressure switch that will cut out the extended range feature if brake cylinder pressure above a moderate amount. The only time you use the engine/independent brakes with dynamics is just before stopping to keep the slack from running out as the dynamics fade out to zero, otherwise both brakes can slide the engine wheels.
You can't use dynamic brakes to hold a train stopped on a grade - if the wheels aren't turning, the dynamic brake system isn't creating braking effort. I believe the independent/engine brakes generally can create about the same braking effort as the dynamic brakes, so adding dynamic brakes on top of the engine brakes for a stopped train does nothing, unless you are slowly releasing the engine brakes preparing to begin movement.
Not to confuse things, but most passenger engines now have "blended braking". When in effect, making a brake pipe reduction causes the engine dynamic brakes to automatically apply (assuming the throttle is in idle). In addition, the engine brakes are also applied by the system, from 10 psi or more depending on the brake pipe reduction, and the how much dynamic braking is being created in relation to speed. Properly functioning, the system balances the combined engine brake cylinder pressure and dynamic braking effort to a safe limit to keep the wheels from sliding. This is how the dynamic braking is usually controlled when a cab car is leading.
