Most of the older gravity-down beds used the area above the piston as a reservoir for hydraulic fluid, and had an air vent at the top of the cylinder. If somebody overfilled the system, the vent would squirt fluid out in a gusher until the volume equalized.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!