Three terms for the same thing. Stuffing box is an old school term from back in the day when most pumps used braided packing. Double posting is against site rules.

Johnny Pellin

thanks. But why i never heard of seal cavity term? is ti because it is rarely use?

sorry for double posting. it wont happen again

I would tend to think of using the term seal cavity as opposed to seal chamber for pumps with an open cavity around the seal such as bell housing heads or tapered bore, open box designs. But, yes it is probably more rarely used.

Johnny Pellin

Rafael Dos Santos,
Since, I work on these parts on a regular basis, I will to explain to you how I look at them.

Stuffing box: Stuffing box is a traditional way to secure packing in place. A packing Gland is used to compress or release packing from stuffing box. The ID of stuffing box contains the rolls of packing while the OD sits against head/cover of pump.
Seal chamber: This is basically a stuffing box modified and changed for mechanical seal upgrade. It can be a completely new design for containing mechanical seal in case or cover of pump.
Seal cavity: Seal cavity is simply the bore where mechanical seal sits. Like you have probably heard about gasket cavity. Gasket cavity is the area where gasket sits. Seal cavity is not a part but a bore on seal chamber where seal sits. Hope this helps!

Thank you MechEngineer2012 for superb explanation..
Know I understand how to differentiate these terms..
Thanks a lot everyone..