Unknown device atop steam loco smokebox

[chuggy]

wjstx:--

Thanx for photo.  The first picture clearly shows the device located forward of the bell.  It is on the centerline of the smokebox top, positioned above the rear edge of the superheater header cover plate.

[wjstix]

A pic always helps, can you see it in this picture, or in this one??

[selector]

If I had to guess, it might be the exhaust pipes rising up from twin air pumps mounted either behind the pilot or above it?  Don't have a photo of this particular engine, so it's just a guess.

Crandell

[chuggy]

Photos of Texas & Pacific 4-8-2s (900 series) show an odd-looking gadget centered atop the smokebox above the rear edge of the superheater cover.  It is circular, rather thin front-to-rear and perhaps approx 6" in diameter.  It appears to have a pipe coming up on each side.  The location seems very unlikely for any sort of gage & I'm wondering if it is some type of pressure regulator.

Looking thru some old editions of the Simmons-Boardman LOCOMOTIVE CYCLOPEDIA shed no light on this device, and few, if any, locomotives of other RRs were so equipped based on photos.  Does anyone know what  that device was & its purpose?