GE Units and Strange Noises at Idle

Trains Magazine General Discussion
1

In one of her posts this week, Mookie asked about “whoop” noises from GE units when at idle and on starting.

Last night, I drove up to Yass Junction, north of Canberra, to check out a new train that is running on the Darwin service in competition with Great Southern’s Ghan, which runs from Adelaide to Darwin. The train uses rebuilt cars from the 1950s and 1960s, but with new luxury interior fittings.

The new train, the “Ozback Explorer” (an abbreviation of “Australian and Outback”) runs from Lithgow, west of Sydney to Yass (from where a bus tour is run to Canberra), then to Melbourne, Adelaide, Alice Springs and to Katherine. It will extend to Darwin when more track capacity is available (new passing loops).

Anyway, like the Ghan, this train uses Pacific National NR class units, model Cv40-9i. The train sits all day at Yass Junction, for about 12 hours. In this time the unit is rotated on PN freights, but when I arrived at 1700 (after work) the unit, NR96 was shut down.

The train carries its own minibuses on flat cars, and once these were loaded, the locomotive was fired up. I took the opportunity to listen for the “Whoop” and sure enough, I heard it a couple of times. The unit was standing still for most of this time and I was standing on a bridge nearby watching passing traffic (not much, but one train in each direction).

The noise seems to come from the rear of the unit, and like other Dash 8s and Dash 9s, the Cv40-9i has an electrically driven radiator fan (in this case two smaller fans) and an electrically driven air compressor.

I’d suggest the air compressor as being the source of Mookie’s “Whoop” noise, when it starts up.

Anybody else like to comment?

Peter

2

that noise is the air compresser motor turning on…
csx engineer

3

Peter,
You’r right, it is the compressor kicking in…
The “whoop” is often followed by a slight hammering, or “knocking” sound from the compressor.

GEs are sneaky, they usually wait till your standing right beside the rear end, before they engage the compressor.
If you have never heard it before, it can startle you.

I dont know if the whoop is the compressor clutch engaging or the compressor’s initial intake of air, but either way, you can hear it from quite a ways off.

Ed

4

Another way to tell if it is GE or EMD when it is slowly coming around a blind corner! [:)]

5

I’d always thought the ‘whoop’ was due to the motor start – you hear a similar noise when some types of electronically-controlled motor start up. Ed’s right, you’ll be startled when the compressor starts – I get startled much more when the little condensate traps do their little bang-and-crackle routine (which I notice much more on GEs than on EMDs – and which, I think, accounts for a more frequent cycling of the air pumps).

6

Overmod! I asked this question before, but never received a good answer and now I think you may have hit it.

They make an electric bug zapper crackle noise (think very small bug) and I often wondered why they make that noise. I am far enough away that they aren’t all that loud, but they just add to the noise. So it is condensation? Doing what?

Mookie

7

I had always thought the “whoop” is heard when the radiator cooling fan (which is in the rear of the unit) turns on.

8

Water collects in the air tanks and the cooling lines.
Whenever you compress “outside” air quickly, it heats up.

Thats part of how a diesel works, by compressing the air fuel mixture quickly and to a high pressure, it can heat up and combust with out a spark from a spark plug.

Do the same to air, compress it quickly and under enough pressure, it heats up.

At that high temp, it isnt useful for the brake system, so it is run through a cooling system, basicly a long run of pipe that allows the compressed air to cool off.

Because the pipes and the storage tank are cooler than the compressed air, the water in the compressed air condenses on the inside of the pipes and the reservior.

Note the way the air reservior is mounted on locomotives…on EMD, the long tank, above the fuel tank, on GEs, the two tanks shaped like big propane tanks on their sides, in the “notch” on the fuel tanks.
If you look closely, you will see they are not level, one end is higher on the EMDs, on the GEs, the tanks slope towards each other in the middle.

This allows the condensation, (water) to collect at the low end, and the “spitter” or evacuation/ water seperator valve draws the water off from the low point.

I assume there is a simple sensor inside the tanks that is set for a pre determined amount or level of water, once that level is reached, the valve opens, using the compressed air in the reservior to blow out the water.

EMD and GE seem to used different valves, GEs seem to “blow down” longer, the EMDs seem to use a bunch of short rapid bursts…

You dont want to be standing directly beside either one, they are loud, and can hurt your hearing, not to mention getting you damp if the outflow pipe is aimed wrong!

Ed

9

Mookie, I think you’re talking about the same thing.

When brake air is compressed, a considerable volume of ‘atmospheric pressure’ air has to be taken in (and filtered). This air will contain some percentage of moisture (humidity). When the air is compressed, it is also heated, and this heat is dissipated in coils or ‘radiators’ ahead of the reservoirs. During this cooling, much of the ‘humidity’ of the compressed air comes out as condensate, which is particularly good at causing corrosion of steel pipe and components. Good practice is to isolate this condensate (usually in a trap at a relative ‘low spot’ in the air piping between compressor and reservoir, but can also be at the ends of reservoirs themselves – a reason, I think, that some GEs have canted reservoirs). The traps are self-clearing (analogous to steam condensate traps) – when they fill up, they bang open, with compressed air rapidly blowing out the condensate charge, and then close up again without wasting a large volume of air. (I think EMD condensate blowdown is longer, and a bit quieter, followed by their air pumps starting and running a bit each time – Randy et al., hop in and expound!)

You could fit the things with mufflers, but that would be added cost, weight, packaging volume, and decreased access for maintenance – so in general GE didn’t.

You may have heard the old story about how the speed of cricket chirps can tell you the temperature – I used to joke that you could tell the relative humidity by the frequency of the trap firings on GEs… haven’t developed a ‘formula’ yet, though ;-}

10

Ed - the Driver has called that sloping to my attention, but he sees things differently than I do, so just said “yeah, whatever!” He will be glad to read this!

I have heard about the crickets and the temperature, but could never remember the formula for that, so guess you are on your own with the GE formula!

This is very interesting. I will print it off and take it train watching, since most of what we see - on good coal days - is a lot of these engines!

Mook

11

That whoop is the compressor…I have seen trains stopped up in Cresson, Pa for crew changes, and you ca hear the whoop and then can hear the compressor…One other thing I noticed, was on a set of light engines sitting in the Cresson engine facility, a NS Dash Nine would occasionally raise its idle speed a bit,perhaps to run one, if that much, and then run that way for a few minutes, then back to low idle…another few minutes later it would notch itself up slightly…and repeat this as long as it was left unattended. Anyone else notice this? What is the purpose of it? Dave Williams http://groups.yahoo.com/group/nsaltoonajohnstown

12

A posting above mentions the differenence in blow-down between GE’s and EMD’s…One thing I’ve noticed, especially on 80MACS, is the rapid pfth pfth pfth ypu hear on them…reminds me of a piece of dirt being stuck in the valve, so instead of getting a blow-off every minute or so, you hear this engine going by doing all this pfth pfth almost constantly. I watched a maintenance man up at the Cresson engine house walk over to one of these pfth’ers, and yank open the valve manually and held it open for 10 seconds to try to clear it…It worked for a minute after that, then went back to its every second quick bursts… Dave Williams http://groups.yahoo.com/group/nsaltoonajohnstown

13

I’m back!

I went for the compressor motor rather than the fan motor because in my quoted example, the unit had just started and it was fairly cool (except in the bright sun) and I didn’t think the water would have reached operating temperature before I heard the first “whoop”. It certainly does sound like an electric motor starting, and the compressor would have the bigger motor, as well. Thanks, everyone.

Because temperatures are generally higher in Australia, the condensate traps aren’t that obvious, although on some units they do operate quite frequently. They can still go off just when you’ve passed one!

Peter

Peter

14

Come to think of it…the whoop sound remindes me of the air solonoid starter, on a truck engine.
Could it be, that there’s a air starter just to get the compressor started? I know that the compressor is powered by an electric motor, but it takes alot of power to start a rotary piston compressor.

15

Hey Mook…you can also tell a GE from an EMD around a blind curve from all the backfireing and explosions.

16

Nice, plus you can see and smell the flames shooting high into the sky . . . [:D] [(-D]

17

I could be wrong, but aren’t all the newer locomotives’ air compressors driven separately by electric motors, where older engines were direct drive from the prime mover crankshaft?

A compressor direct driven by an engine never stops running, but is “unloaded” by a small piston in the cylinder head that at a given pressure holds open the inlet valve. This means a compressor taking a load would begine to make pumping noises - kathunk, kathunk, kathunk, but not any of the noises associated with startup of a motor.

Air brake systems have two tanks, supply, and service. Supply tanks are for settling of condensate and whatever else might be in the air. The service tank is then for storage of clean air.

18

Oh, I suspect cycling of idle speed may be to reduce the effects of long idling, which can cause varnishing of cylinder walls, but probably it it is more to do with temporary loads from auxiliary equipment.

19

Or maintaining the prime mover at operating temperature. Beginning with dash 8 locomotives , the air compressors are motor driven along with the radiator fans. Every one is correct about the sound the air compressor motor makes when it starts. The radiator fans make a similar but more prolonged starting noise. The amount of air moved by the big GE radiator fans is tremendous, if you are testing one it’s a good idea to exit the front of the locomotive and avoid walking past the radiators or you may have your clothing stripped from you.
The main res blows are really pretty simple, a magnet valve operates each time the air compressor operates, one blast as the compressor turns on and one when it turns off. The exeption is the CSX who uses a spitter type valve which is faster and random. Some blowdowns are operated by little Salem timers which operate every 60 seconds or so. Winter time is coming so we need to get our fusees ready to thaw these valves when they freeze up.
Randy

20

Are compressors usually powered by single phase or three phase power? I would assume three phase is available on A.C. units but probably not D.C. units. It would be hard to start a big electric motor without a third phase I would think. Do air tanks on trains use electric spitter valve or do they just have a moisture trap?
Anyone?

Dave