I am trying to help identify a Pullman's Palace Car air gauge from a museum collection.
The gauge dates from 1889 to 1899 and measures approx. 6 inches across.
Anyone know what it was used for in a Pullman car? Pullman generally didn't use Pullman guages for the brake system air (usually those were
Westinghouse or NYBC gauges), so it may be part of a water pressurizing system, but I'm not sure.
Any info would be appreciated.

It is common to have a brake pipe guage in private cars - let's the people know if the brakes have been applied or released.