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A variable-buoyancy pressure vessel system is a type of rigid buoyancy control device for diving systems that retains a constant volume and varies its density by changing the weight (mass) of the contents, either by moving the ambient fluid into and out of a rigid pressure vessel, or by moving a stored liquid between internal and external variable-volume containers.
The ASME definition of a pressure vessel is a container designed to hold gases or liquids at a pressure substantially different from the ambient pressure. [2]The Australian and New Zealand standard "AS/NZS 1200:2000 Pressure equipment" defines a pressure vessel as a vessel subject to internal or external pressure, including connected components and accessories up to the connection to external ...
The partial pressure gradient, also known as the concentration gradient, can be used as a model for the driving mechanism of diffusion. The partial pressure gradient is the rate of variation of partial pressure (or more accurately, the concentration) of the solute (dissolved gas) from one point to another in the solvent.
Positive pressure is a pressure within a system that is greater than the environment that surrounds that system. Consequently, if there is any leak from the positively pressured system, it will egress into the surrounding environment. This is in contrast to a negative pressure room, where air is sucked in. [1] [2]
Gas is breathed at ambient pressure, and some of this gas dissolves into the blood and other fluids. Inert gas continues to be taken up until the gas dissolved in the tissues is in a state of equilibrium with the gas in the lungs (see saturation diving), or the ambient pressure is reduced until the inert gases dissolved in the tissues are at a higher concentration than the equilibrium state ...
The pressure potential in a plant cell is usually positive. In plasmolysed cells, pressure potential is almost zero. Negative pressure potentials occur when water is pulled through an open system such as a plant xylem vessel. Withstanding negative pressure potentials (frequently called tension) is an important
Negative buoyancy may also be useful at times to settle the vessel on the bottom, and positive buoyancy is necessary to float the vessel at the surface. Fine buoyancy adjustments may be made using one or more variable buoyancy pressure vessels as trim tanks , and gross changes of buoyancy at or near the surface may use ambient pressure ballast ...
The ambient pressure underwater varies with the depth, and diver attitude in the water can affect the variation in pressure between the lungs and the delivered gas in the mouthpiece by up to about 250 mm water (25 mb), but usually less, which can be positive or negative depending on the relative position of the lungs to the demand valve ...