What Are These Glass Bulbs

Here comes maybe an interesting question. I noticed some sort of glass bulbs attached near bogies of prettymuch all freight locomotives so anyone knows what is their purpose?

It's by no means a new addition (according to some old photos) but I only noticed it now.

 

Maybe to show moisture in the air system for the brakes? I know with trucks you’d drain the air reservoir every now and then to get rid of moisture.

 

Yeah, that seems like a good possibility.

 

Ok so I took another look today (as the loco didn't move) and there is actually a light bulb tucked in the top piece so it's probably just a light and nothing else. Still pretty weird placement though.

 

I was thinking more of a glass bowl that collects moisture/water rather than an actual light bulb. Maybe I was way off.

 

I wonder if Google Lens will know​

 

Definitely looks like a water separator/sediment bowl. My 9-5 job is doing parts for farm equipment and it looks a lot like a fuel bowl that serves the same function (removes water from fuel), except in this case, as noted, removes water from the air brake lines.

Here's a fuel bowl on a Ford 3930 tractor for comparison...


Other systems used that perform the same function of removing moisture from air lines would be Spirax valves (familiar to those in the UK) and Air Dryer systems (the sputtering sound you hear on North American locomotives).

EDIT:

Ignore all of that, it's a lamp. Look reeeeaaaaalllyyy closely on the first picture and you can see the tip of the bulb hanging down.

 

I was looking through my train documentation collection and found something that can probably wrap this up. In a manual for the ČD 363.5 (which also has these things installed) there is a picture of a panel that clearly shows a "bogie lights" switch.