low idle, high idle..?

Trains Magazine General Discussion
1

I’m confused by something.

Sometimes I hear EMD 645 engines just sitting there in run 1, and then starting to roll without going to idle to switch to front “gear”

Do some engines have run1 RPM as their idle.
Is idle RPM adjustable on these engines? And if yes, when is it done and why?
.

2

The RPM in idle can be the same as the RPM in run 1. Moveing the throttle from idle to notch 1 enguages the juice to the traction motors. But the RPM settings for each notch can vary.

3

Yea, that’s what I’m asking

So each railroad may use different RPM?

I have a couple of subquestions then, if you have answers please specify the number of the question so that I know which one are you answering:

  1. How is RPM tuned?
    2.When you change the RPM of the Idle, does that mean all other notches have increased/decreased RPM?
  2. Is there some kind of default RPM for each notch specified by the manufacturer?
  3. Which major american railroads do this kind of stuff (set the RPM differently)?

thanks

4
  1. On modern (current production) units, this is done by rebooting the control module then adjusting the settings accordingly. BUT do not try this without a member of your railroads local “flying squad” to lead you through this process the first time-or else! 2. No. 3. Yes. 4. All of them! NS is the most prominent, but they all do this at one time, or another
5

Thanks. That leads me to:

  1. Why do they change the Idle RPM? And do they usually increase it or decrease it from default?

  2. You say all RR’s do it at some point. Can you think of a couple of first class RR’s that do what I described in the first post (have the idle running at same RPM as run1 on EMD’s) ?

6

The differance is more by the model type then the railroad. I am no expert so keep that in mind.

Here is a site with various loco manuals that would have specific information:

http://www.rr-fallenflags.org/manual/manual.html

I can’t really answer the question in that format. But I’ll try to explain it the way I understand it. I’m sure Randy S. could answer this as he is a experienced loco mechanic. I am not and this is just from observation. So till then…

The way the MU throttle works is similar to digital to analog conversion. There are 4 lines on the MU cable that connect to the governor of each locomotive. Each of those four connections and there corresponding governor valve settings (A,B,C,D) has a ‘weight’ to it. The combination of these lines / valves will determine the total throttle. If A is the least significant valve then it will have the least effect. If D is the most significant valve it will have the most effect. I don’t know the RPM numbers so I’ll use nice round numbers to try to explain. Say A has a factor of 1, B-2, C-4 and D-8. If valve A is on then you would be at say run 1. Then if you advanced the throttle to 2 then A would close and B would open. The ‘weight’ af A alone would determine the RPM and can be adjusted by some means. The same would go for the B valve alone in run 2. But for a factor of 3 a combination of the A valve and B valve together would determine the RPM and would be dependant on what the individual settings of each of the A and B valves is. Then the next notch would be 4 and the C valve with the factor of 4 would be on by itself and its setting alone would determine the RPM. Then for the next notch, 5, the combination of the C and A valves (with weights of 4 and 1 for a total of 5) settings would determine the RPM. And so on and so on…

Again this is just

7

I hope Randy Stahl jumps in here–he’s the guy that ought to know.

I was under the impression that “default”, as you call it, was the same for all EMD 645s, and is the same for each and every engine type out there. It isn’t changed–you m.u. three locomotives of the same builder, and they’ll all sound the same, because they’re running at the same RPM in each throttle session.

And, yes, Run 1 is the same RPM as normal Idle.

Low Idle is something different–engines will slow to a “low idle” setting after a certain length of time in idle, or when the reverser is centered. Saves a bit of fuel.

8

Old school way to do it is adjusting the mechanical fuel rack. AKA: Turnin up the fuel. Just like Joe Goober can do on his older diesel pickup.

Adrianspeeder

9

Most, if not all, microprocessor-controlled 710 engines have a low “neutral-idle” speed, where the throttle is in idle and the reverser is in neutral. SP’s 645-powered GP40M-2 units rebuilt by MK Rail do this as well.

10

Hi, could you elaborate on that?

Does that mean that when you put the reverser to forward, the RPM goes to run1 RPM?
Or what?

11

No, on older locomotives with the woodward PGR governers , low idle was accomplished by energizing the A and the D solenoids in the governer. When the reverser handle is thrown in forward or reverse the engine goes into NORMAL idle ( around 360-400 rpm) . The locomotives that have this feature also have a NIR relay ( normal idle relay ) to activate when the reverser relays move.

There is another feature sometimes found on older locomotives called an LIP (low idle panel) . This system has a temperature sensor somplace that decides when and if the engine will run in low idle or not.

On newer locomotives (microprocessor) , the computer determines the best RPM for the conditions, some EMD’s and GE’s will sometimes only have 4-5 different engine speeds, this is very true on GE’s to stop excessive smoking.

Notch one is normal idle .

Randy