A diving backplate includes a device body, a first frame, a second frame and multiple counterweights. The device body includes an inward face and an outward face opposite to the inward face. The first frame is connected to the outward face. The second frame is connected to the inward face and includes multiple first assembly holes. The multiple counterweights are detachable mounted to the second frame. Each counterweight includes multiple second assembly holes each respectively aligned with a respective one of the multiple first assembly holes. A fastener is provided for mounting with each aligned first assembly hole and second assembly hole.

A back plate for a breathing apparatus comprises a back plate frame for supporting a cylinder of breathable gas; and a pressure reduction valve configured to receive breathing gas from a cylinder of breathable gas; and a resiliently deformable element configured to support the pressure reduction valve on the back plate frame so as to permit relative movement between the pressure reduction valve and the back plate frame.

A buoyancy compensator bladder includes an air cell, a connector, a low-pressure inflator (LPI), and at least one over pressure valve. The LPI which inflates and deflates the air cell is positioned on an outer surface of the air cell. As a result, when the fully assembled buoyancy compensator is equipped by a diver, the LPI runs from behind the diver's torso and under their armpit. This results in the inflator head which is part of the LPI to be disposed on the front of the diver's chest during back mount or side mount diving. This structure allows the bladder to be easily used for either back mount or side mount diving. The bladder may further be equipped with auxiliary/non-essential devices such as wight pockets/pouches.

A backrest for a scuba diver comprising: a strap, having an upper right portion fitting around the diver's right shoulder, an upper left portion fitting around the diver's left shoulder and a lower portion fitting around the diver's abdomen, a right adjustment block between the upper right portion and the lower portion, and a left adjustment block between the upper left portion and the lower portion. Each of the adjustment blocks has a first pin engaged in a first loop of one end of the upper portion, a second pin engaged in a second loop of one end of the lower portion, a clamp clamping the lower portion of the strap to block the sliding of the end of the lower portion of the strap around the second pin, and a handgrip actuating the clamp between blocking and unblocking the sliding of the end of the lower portion of the strap around the second pin.