What makes the zapping noise on diesel electric locomotives?

Question

When I see diesel locos moving slowly or idling, I often hear an electrical zapping sound coming from it. Is it from the traction motors?

Answer 1

What you are most liking hearing is air from the air compressers that will make a loud like zapping sound.Traction motors don"t make any noise when siting at a idle.

Answer 2

hoghead is exactly right!

Answer 3

In the UK it used to happen in the days of steam locomotives as well, if the loco had a Westinghouse brake system. That used a reservoir on the side of the loco which made a 'popping' noise whilst the loco was idle.

Answer 4

Hoghead gave another great answer.... Air needs to be as dry as possible in order to extend the life of air brake equipment...Along with automatic drains most locomotives have air dryers which remove most of the moisture in the air system...

Answer 5

railrunner is on the right track (no pun intended).

The main air reservoir has air operated, automatic condensation releases for getting rid of the unwanted moisture that collects in the reservoir.

The condensation is created when the air that comes from the air compressor, which is hot, travels through the after-cooler on its way to the main air reservoir.  As the air cools, condensation occurs and the result is water.

Most describe it as a "popping" sound, but zapping plays just as well.

Good question.