Bcd Scuba Buoyancy
Bcd Scuba Buoyancy
How does a SCUBA BCD work?
OK, so you shoot some air into the BCD, and it makes the diver more buoyant, right? But aren't we talking about the same amount of air...just moved from the cylinder to the BCD? Does buoyancy change that dramatically when the air is no longer compressed?
Archimede's Principle says that when a body is immersed in a fluid, it's subject to a force up-warding. The intensity of this force is given by the volume of the body and an equivalent mass of water.
Let's make an example.
For simplicity I am using the metric system.
I'll measure the volume with liters (a liter is the volume of a cube with an edge of 10cm=4inches), and weight with kg (a kg is the weight of 1 liter of water).
Everything has a volume and a weight. If the ratio of volume and weight in liters and kg is 1, then we have something that weights like water. If it is less than one, it means that it's heavier than water, if greater than 1 it is lighter.
A fully equipped scuba diver (suit,weight, tank, bcd,regulators) can weigh about 100 kg (more or less 200 pounds). That means that there is a force that pulls him downwards with a 100kg strenght
If it's volume is 100 lt (more or less 25 gallons), according to Archimedes, there is a force of 100lt of water that is pushing him up. What is the force of 100lt of water: exactly 100kg.
Given this, inflating the bcd will raise the volume of the diver, that is the pushing up force is larger than the pulling down: the diver go to the surface. Viceversa, deflating the bcd will decrease the volume so the pulling down force is stronger: the diver goes deeper.
Now... how come the volume increase when you inflate the bcd: you get the air from the tank and move it to the bcd, so should be the same. The difference is that air is a gas, and gases can be compressed: you can see it using a empty (i.e. full of air) plastic bottle. Even if it is well sealed, you can squeeze it. If you try the same with the bottle full of water, you will see that you can't squeeze it. That is because only gases can be compressed, while liquidsa and solids not.
But what it means to compress a gas: it means that you can reduce its volume, without loosing any gas: you can decrease the volume of a bottle of milk, by drinking it... with air or any other gas, you can decrease the volume, without breathing the gas.
When you compress a gas, you raise its pressure: the higher the pressure, the lower the volume. So what happens: in the tank we have highly compressed air: at least 50 to 200 bars. In the bcd we have low compressed air, usually 10 bars more than the ambient pressure (at 50mt depth, it means that the air pressure is 15 bars).
So the air in the bcd, being at lower pressure than in the tank, is larger (in volume) and you get morepush upp force...
A final consideration: remember that the tank is in metal, not fabric. When you take air out of it it doesn't change its shape (and consequently its volume) , while the bcd, being soft, will change its shape and its volume.
Luca
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Scuba diving is a fabulous sport to get involved in, but there is a down side - the equipment isn't cheap. If you're planning to do a lot of scuba diving, then you also need to allow for the costs of buying your own equipment.
When you're many meters under the surface of the ocean, you need to be confident that you have the right gear and that it won't break down unexpectedly. So buying good quality scuba diving equipment is important. Still, if you spend some time looking around, it's possible to still buy good gear at cheaper prices. You're going to need a few things, so if you manage to save some dollars, even if it's only on some of your gear, it all helps.
One piece of equipment you need is your mask. This is your window on the underwater world, so make sure it fits snugly and gives you a clear view. Over time a mask does tend to get scratched, so this is one piece of equipment you might not want to buy second hand. You also need a regulator, to help you breathe underwater. Basically, it takes the compressed air in your scuba tanks and reduces the pressure down to a level that is breathable. It only delivers air when you inhale, so that you don't waste the air in your tanks.
Another important piece of equipment is your buoyancy control device, or BCD. It's worn like a vest, and contains an expandable bladder that you inflate with air from your tank as you're diving. This is mandatory, because as you dive deeper, the water pressure increases. So unless you can increase your buoyancy at that point, you will start to sink like a stone.
Unless you're only diving in shallow, warm tropical waters, you're going to want a wet suit. This works efficiently to keep your body temperature at normal levels. The wet suit helps your body to deal with the increased water pressure at depths and also the colder temperatures. Some people are comfortable with a body suit, so that may suit you better. Either way, you end up with a skintight outfit that clings closely to your body.
Again, unless you're only diving in shallow water, you'll need a torch. You can pay anything from $20 right through to thousands of dollars for an underwater torch, so do your research. Having a good torch, though, really makes it easier to see the beauty that's hidden beneath the water. The deeper you go, the less sunlight, and so the less color. It can be quite astounding to look at a bland, brown piece of coral deep under the ocean, only to highlight it with a torch and see it blaze with color.
Most scuba divers like to carry a knife. It's not an essential item, but can be used for digging or prying things. Remember to check whether it's okay to disturb the natural fauna where you're diving. A knife isn't meant to be used as a weapon underwater, unless it's absolutely necessary.
If you're not sure exactly what you need, head for your nearest scuba store and start asking questions. They will be able to assist you with choosing the right gear for your level of experience and the type of diving you're expecting to do.
For more scuba diving related resources and information on the dangers of scuba diving to include nitrogen narcosis please visit www.best-scuba-diving-resources.info where you will find helpful tips and advice on choosing your scuba diving mask, fins and scuba diving wetsuit.
Many thanks for reading our Bcd Scuba Buoyancy article
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