[babygene]

“Volume remains constant.”

You are confused...

Lets suppose the ambient temperature is 250 degrees. The ball is filled with 50% water vapor and 50% air. With the absolute (gauge) pressure at 12.5 PSI.

You now reduce the temperature to 150 degrees... The water vapor now condenses to liquid H2O. What’s the pressure in the ball?

Got it? It’s close to 6.5 PSI... Of course the volume remains more or less constant, but the pressure doesn’t. It conforms to Dalton’s law of partial pressures.

[Smokin' Joe]

The volume of the bladder in the ball didn't change, now did it? You are the confused one.

Btw, those are GAS laws.

If you want to play with phase changes, of course the rules are different.

And where are you going to fill the ball with 50% water vapor?