Idling locomotive sound

[NPloysa]

So the past few times I have ridden the light rail here in Denver, I have noticed a popping sound coming from nearby locos at the UP yards at certain light rail stops. They are idling and seem to "pop pop pop". What is it? I know I can hear the cooling fans sometimes too. These are mostly AC4400s, SD70s, 80s, 90MACs. Any ideas?



Nick

 

[DennyDay]

Air system pop offs that eject moisture.



Denny

 

[nickleinonen]

constent popping to me seems to be a spitter valve. they are mounted to the main resovoirs instead of electronic blow down valves. the spitter valve is a mechanical device to attempt to remove any free water in the system that may have collected from condensiation after the air dryer. they work somewhat well, but make noise [especially in an enclosed shop- first thing i do when i get one with a spitter is to drain all the system air]. they are also sometimes mounted to the centrifical air filters that are mounted below the running boards feeding air into the cab [older power has an 818 and 824 model filters, newer ones have a pair of 824's].



and if you get a spitter that is not spitting, but just blowing, a good hard smack with a hammer against the face of the spitter vave will 90% of the time get it going again.

 

[NPloysa]

Cool, thanks. Are the air dryers similar to the ones on Class 8 trucks?



Nick

 

[EMD Diesel Power]

Air dryers tick and pop at paired intervals... . one side blows... then the other blows around 20 seconds later... ... I think it repeats every 5-10 mins. Blow-off/auto water drain valves on the main res tanks are the random poppers/spitters. This also depends on the railroad and the type of dryers installed.



Spitters didnt bother me as much as those #@$%! #@$%! #@$%! sticking horn valves when recharging the system with shop air. All we could do was let the damn thing blow for a few seconds to build enough pressure so I could either whack the valve or yank the whistle handle a few times and have it reset itself. :-laf :-laf

 

[nickleinonen]

sticking horn valves when recharging the system with shop air.

:-laf:-laf... yeah, that is annoying at times. as is when we get forign unit [ns, up, bnsf... ] with the bell and horn switchs with swapped colors and positions from what we have on our power. them horns when blowed inside the shop is loud [especially when you are on the roof doing a spark arrestor inspection]



the air dryers work somewhat similarly to the truck ones, just much larger in size. the twin tower dryers we use on the emd's weigh 114lbs. . here is the air dryer that is on most of our power

 

[NPloysa]

Nick, how do they work? Is there a heater and filter in there? I know the purpose, just not what's all involved.



Nick

 

[2-ND TIME]

locamotive sounds

Well I worked for ( cheapy rail) Canadian Pacific for 6 months as electrician out of Vancouver BC on the AC 4400 locamotives for the most part. Well I think what you are hearing is testing of each cylinder ( it injects 10 % more fuel into each cylinder in order for 3 or 4 cycles and then pauses and goes to the next cylinder. ) can't remember what the test is called it is to check that they work it is part of the 90,180,270 day checks. The fans coming on is part of the same test for the cab of the locamotive. Do you hear them going to full power this is to test that the dynamic braking is working. The exhausts on the turbos really do turn orange at full power.

Or if there is other problems that the engineer reports that a loco isn't doing. There were 4 or 5 times that I say something wrong with a loco that was supposed to be going out from service. ( I was worried that the bosses would be mad at me for finding something wrong with one that should be ready for service) The bosses were very good to work for, guess it wasn't soooo bad

 

[SHobbs]

Whats really fun is walking by a loco and the spitter decides to puke alot of water at one time instead of one small shot every one and then.

 

[nickleinonen]

Well I think what you are hearing is testing of each cylinder ( it injects 10 % more fuel into each cylinder in order for 3 or 4 cycles and then pauses and goes to the next cylinder. ) can't remember what the test is called it

pop test. . it has a distinct sound, as you make the cylinder hammer hard, and you don't hear that when the engine is normally running [or on an emd engine] although if it was a 16fdl electronic engine, they go into emissions idle and kills 12 of 16 cylinders rotating the firing 4 cylinders around to make sure they all get a chance to fire, and it will come out of the 4 cylinder idle when the air compressor wants to start up or the cooling fan wants to start up and you get a ugly lopey idle that rocks the entire unit

Whats really fun is walking by a loco and the spitter decides to puke alot of water at one time instead of one small shot every one and then.

yeah, that is great fun