when commuter trains run push-pull is there a difference in how the train handles in push vs pull?
also, any differences in operating the train (speed , curves etc)?
One difference of which I am aware is that the engineer cannot use the independent brake when the train is in the push mode. As a regular passenger, I’ve noticed that there seems to be a bit less control of slack action when pushing.
Can’t answer the first part, but here in the UK there has been 125 mph push-pull operation for years (8/9 passenger cars with a 6000hp electric loco at one end) - and the schedules are the same whichever way round the train is operating.
Tony
In the Metra cab-cars there is an “independent” brake of sorts. It is called a parking brake, and it is used during station stops to hold the train, allowing the brake system to recharge during the stop.
It is an all-or-nothing type of valve, and it puts 90psi (nominal train brake pipe pressure setting) of main reservoir air directly to the brake-pipe on both trucks of the cab-car only. It works ‘independently’ of the automatic brake valve, despite the fact that when the parking brake is in use the cab-car brake-pipe air gauge shows brake cylinder pressure, regardless if the air is from the brake-pipe reservoir or the parking brake.
The only operating difference is that one cannot “bail off” the independent in a cab-car when the automatic is applied: the cab-car wheels set just like any other coach. However, one can activate the ‘parking brake’ on top of an automatic application, and the result will be an increase of pressure to the cab-car brakes only, and is almost guaranteed to cause the wheels to lock and slide, resulting in flat-spots on the cab-car.
The slack action is rather similar to that of the locomotive independent brake in that if the station is not on level ground, the coach slack will behave the same, rolling toward or away from the controlling unit.
There is no difference in operations regarding any temporary speed restrictions, speed limit around curves, over interlockings, etc.
And just for reference, when operating from the cab-car, the leading end of the train is considered the “front”, designated by an “F” on the cab-car.
Thanks for the good answer Zardoz. I was not aware of the independent brake/parking brake in the cabs cars. A couple of questions… Is the parking brake a new feature on the cab cars that Metra has recently purchased, or has there always been this type of brake in the cab cars? Also, is the parking brake ever used when the train needs to make an emergency stop?
Thanks,
CC
Chris30,
The parking brake has always been a feature of the cab-cars. One the very first ones the CNW bought, the parking brake only set the brakes on the leading truck. This was found to be insufficient to hold a longer train at certain stations, so theyy were modified to actuate the brakes on both trucks of the cab-car.
The parking brake can be used during an emergency stop, but unless the rail is extremely dry, and sometimes even then, applying the parking brake on top of an emergency application will only result in causing the wheels on the cab-car to pick up and slide, actually REDUCING the braking effort, and creating nasty flat spots on the wheels.
On NJ transit the cab cars are equipped with an automatice brake valve the same as in the locomotive. Operation is basically the same whether the engineer is in the locomotive or cab car but train handling differs somewhat because, in the push mode, the heavy end (locomotive is on the hind end rather than leading) and it can change the way slack is handled. Operations can be as smooth from either end depending on the engineer and the mechanical condition of the train.
Steve
And a bit of trivia about Metra cab-cars:
They actually have a good-old-fashioned pull cord for the whistle. Not a lever like on the older SD’s, and not a (shudder, yuk) frikin’ push-button like on the new units. An actual pull cord (like in the old geeps), connected to the air valve which is on the inside of the roof of the cab-car.
The cab side windows of the cab-car slide open; and there is a small (about 1’x1’) opening on the bottom of the doors leading from the coach seats to the operating cab. When the window on one side is opened while the train is moving, it creates a huge airflow under the door on the opposite side of the cab. This condition led to one the more common practical jokes we would play on deserving grouchy old engineers: the setp would include placing a nice amount of debris (ashes preferably) just in front of the door of the intended victim. Then, at an appropriate time (best if you have an actual reason) you pen your windxow, sucking in all the debris you placed at the mark’s door opening, and he gets covered with all the debris. Nasty, yes; but some of them SO deserved it.
of huge interest to me ,in australia we only have rear assist loco,s in the push/pull mode (both ends at once)