Sherwood SCUBA rep.:
Aluminum can not be over filled. Whoever told you that is wrong. On aluminum the service pressure is what is stamped on the cylinder.
The service pressure is what is stamped on the cylinder REGARDLESS OF WHAT IT IS MADE OF! It is just as safe (or unsafe) to overfill an aluminum cylinder as it is to overfill a cylinder made from anything else.
ALL SCUBA CYLINDERS are subjected to exactly the same DOT test. They must withstand 10,000 cyles to 4/3 of the service pressure, then they MUST fail at some point after the 10,000 cycles in a "leak before burst" failure mode. An aluminum cylinder cannot be "under designed. (if so, it will not withstand the 10,000 cycle test) A steel cylinder cannot be "under designed". (if so, it will not withstand the 10,000 cycle test) An aluminum cylinder cannot be "over designed" (if so, it will not fail at all, therefore, it will not acheive the mandatory LBB failure mode after 10,000 cycles). A steel cylinder cannot be "over designed" (if so, it will not fail at all, therefore, it will not achieve the mandatory LBB failure mode after 10,000 cycles).
I am not discussing the merits of overfilling or not overfilling any particular cylinder. I am simply saying that REGARDLESS OF WHAT THE CYLINDER IS MADE OF, it is equally safe (or unsafe) to overfill a scuba cylinder.
Another Note: The business about overfilling 10% for the first year, and not on subsequent years, and about when you must and must not switch to DIN valves.....well, that is simply the uninformed attempting to inform. If this is your local scuba stores rule, it is THEIR rule....not any kind of industry, CGA, or any other organization.....standard.
Phil Ellis
