What is this bladder & check valve for?

[GuySmilie]

This is a totally different subject, but I've wondered about this for so long that I have to ask.
What is the function/purpose of the mini bladder tank & 4lb rated check valve highlighted in the red box?

http://www.reefugium.com/pix/mini_bladder_check_valve.jpg

If I were a cat, I would be dead by now :D

[SpectraPure]

Although we do offer a three-piece ASO kit ( ASOV, check valve, and float) to compete with others on price for the same, we find that at least an MBTA (or a real storage tank) is needed for the best operation. It provides some reserve water so the "weeping" or "chattering" that mechanical floats do just before turn-off and at turn-on don't get amplified and drive the ASO crazy -- banging like water hammer in a plumbing system. Solenoids don't need it because they turn-on and -off quickly and cleanly.

The check valve is used here to give priority to the sump. Only when the sump is full will the water break through the check valve and fill the barrel.

Scott
SpectraPure, Inc.

[GuySmilie]

Thanks Scott.
That makes sense to me.
Due to its small size, my initial instinct was that it simulated hysteresis, like the little rigid copper ballasts used at faucets in conventional home plumbing. Now I know.