In the August, 2001 TRAINS on page 48, he says “IDP (Integraged Distributed Power ) allows railroads to run larger trains downhill, because the remote units can recharge the train air–not possible with manned helpers.”
Why is this true?
Do they even hook up the brake hoses for helper service? Seems like there would be some concern about pulling the train in two since the car nearest to the brake control always brakes a tad before the next car further away, etc etc. Seems like if you had a brake application starting from the rear of a heavy train, someone would spend a lot of time changing knuckles…
Yes, the brake hoses are connected in helper service to if the train parts and goes into emergency the helper units also go into emergency and stop pushing which could cause a derailment. Some helper operations now use a feature called Helper Link which is a box mounted upon the helper units platform walkway and attached to the helper unit’s brake pipe. It is electronically to the controlling locomotive of the lead consist like the head end and rear of train device are. If the engineer dumps the air on the rear of train device or the train hoses part and the rear of train device air is dumped then the Helper Link senses the loss of full air pressure and dumps the air on the helper locomoteves as well. This Helper Link box is the connection of the helper air brakes in lieu of the direct connection via the brake pipe.
In manned helper operations, helpers not attached to the point of the train will have their feed valve in the cut out position. The feed valve is the control that allows that locomotive to pump air into the brake pipe. Only one can be cut into the train so only that locomotive engineer can control the application and release of the trainline airbrakes. If another feed valve is cut in then when a brake pipe reduction is made to set the brakes the second feed valve would allow the trailing units to pump air into the brake pipe to maintain the trainline brake pipe pressure the Engineer wants to reduce to set the brakes. That would never be a good idea.
With DPU, the feed valve on the lead locomotive of the DPU is also cut in to allow those units to feed air into the brake pipe. That sure seems to conflict with the last paragraph doesn’t it? With DPU the lead engineer has electronic control of most of the functions of the trailing DPU consist including the air brakes. So the DPU feed valves work almost exactly the same as the feed valve on the lead locomotive. When air is set on the lead unit, it is also set on the trailing DPU consist. If the air dumps on the lead
I thougt all IDP’s where always in the middle,and the main reservoir has to be cut in to continue the main train line.In pushers service they are of course in the rear,and yes all the air is cut out,and all the air is controlled from the headend unit.I can see that the air would help charge the train.I have been on a train with pushers on the rear before and had to wait till the pusher cut his air out on the control stand.The pusher engine is the same as another car as far a the air is concerned.So if it does come uncoupled it will put the train in emergency.In other words it just like a trailing motor in the headend consist.[2c]
The IDP or DPU units can be any where in the train. If they are in the middle the angle cocks on both sides of the DPU are left open so the train line is continuous. The feed valve on the DPU is still cut in on this consist so as to allow the DPUs to charge the trainline as well as to set the air at that point. Remember the engineer on the lead unit still has control of the DPU locomotives. The same is true when the DPUs are at the rear of the train. It is only when the helpers are manned by another crew that the helper unit feed valves are cut out before the train can move.