Abstract: A gas control valve (802) has an inlet needle jet (812) and an outlet (816), the communication between which is controlled by a valve member (808) carried by a rod (807) connected to a diaphragm (804) which divides a chamber (806), open to ambient pressure, from a chamber (805) which has an inlet connected to a buoyancy chamber (100) of buoyancy apparatus in which the valve is incorporated. The inlet (816) is also connected to the buoyancy chamber (100). By the inclusion of an ascent sensing control valve (801) sensing to trigger a venting valve (106), the buoyancy control apparatus is capable of producing hovering in water.

Abstract: A water craft including an inflatable buoyancy chamber, by inflation and deflation of the buoyancy chamber the buoyancy of the craft, floating or submerged, can be regulated. The water craft includes a buoyancy control apparatus for controlling inflation and deflation of the buoyancy chamber via air supplied by a source of compressed gas. The buoyancy control apparatus includes an operator actuable control which sends control signals to a venting device, to a descent device, to an ascent device or to a hovering device.

Abstract: Buoyancy apparatus for carrying a payload to and maintaining the payload at substantially a constant depth or within a desired range of depth, which comprises a variable buoyancy vessel, a depth sensor, deflectable members for detecting upwards and downward movement respectively linked to a gas supply to increase the buoyancy by displacing water from the buoyancy vessel on detecting downward movement and to decrease the buoyancy by operating a release valve to vent gas from the buoyancy vessel on detecting upward movement, and apparatus for preventing said buoyancy variations commencing until the depth sensor senses that the payload is at a predetermined depth.

Abstract: A device for venting gas from an expansible gas chamber (lifejacket, lifting bag, etc.) of an underwater buoyancy apparatus. The device comprises a monitoring device which monitors the rate of ascent of the expansible gas chamber and provides a control signal when the ascent velocity exceeds a predetermined speed. A venting valve assembly controls the venting of gas from the expansible gas chamber and is responsive to the control signal to vent gas reducing the buoyancy of the expansible gas chamber.

Abstract: A device for automatically opening a gas supply valve when the device reaches a predetermined depth, e.g. when diving, has a gas reservoir, a pressure sensing means providing a control signal when the ambient pressure exceeds that of the gas reservoir, and a supply valve which is opened upon receipt of that signal. A preferred embodiment has a flexible diaphragm exposed at its faces respectively to the ambient pressure and to the gas reservoir pressure, and arranged to move an actuator which acts directly or indirectly on the gas supply valve. Underwater buoyancy apparatus, for use for example by a diver, has a buoyancy chamber to which as can be supplied to alter buoyancy, and the device is incorporated between a gas supply and the buoyancy chamber to give automatic increase of buoyancy when a predetermined depth is reached.