a real spitfire..

[cabforward]

watching old csx emd switchers at work, i hear noise that sounds like air 'popping' 2-3 times quickly every 20 seconds.. engine is pulling short loads and moving 10-15mph.. the noise reminds of old-style pressure cookers that released air in rapid-fire bursts..

any ideas on what causes the 'popping'? never heard it in the '60s or '70s..

[Anonymous]

What you're probably hearing is called a "spitter valve". On the old-time diesel switchers, the main air reservoir had a simple drain valve on the bottom. The engineman or shop people were toopen the valve once a day to drain out the water which had accumulated during the last day or so. GP's and F's and such had an automatic drain which would "phhhhhttt!" every so often. The spitter valve, as you described it, does just that. Much more frequently than the old auto drain, the spitter "pops" about every 20sec. or so. It is much more efficient at removing moisture from the air system. Great when it's working right, but when it goes bad, the spitter becomes a continual blow.

[Anonymous]

Not to mention being a real headache for the hostlers...... A fellow that I knew, when he first came upon one of these new units he thought there was something wrong with the blow off, so he took a hammer to the valve in an attempt to fix it. Well, about ten minutes later, he had a broken air pipe that required that unit to be shopped......
Todd C.