Bcd Buoyancy
Bcd 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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I have a mantra when it comes to buying diving equipment, "buy the right to buy once." Of advice, especially when it comes to computer support life. Buying a BCD is one of the most expensive components of the most recreational divers will. It is also one of the highest when it comes to cleaning and maintenancing. She is a frequent phenomenon to be with someone dressing for a dive, watch your BCD and see "salty crud" stuck outside. You can only imagine what the infestation of life within it. This lack of "maintenance" is not only foolish financially abundant is also a safety issue. There are many components of a BCD to be clean and well maintained, correct and secure execution diving. Think about it, nothing scares me more than inflation hit a button and a flexible oxidized low inflation pressure to be quickly disconnected before climbing out of control.
Some tips to keep your equipment in good working condition:
1. Have a professional technician servicing your BCD Scuba regularly and at least according to the manufacturer's specifications.
2. Make sure it is adjusted well and is properly trained to use equipment.
3. Disconnect all finished tubes after diving. Inspect and clean all pipes including corrugated pipe for damage, cuts, cuts and splits. Remove and inspect the weight pockets. If the velcro weight pockets, Velcro and then inspect and clean with a toothbrush. Do not let dirt on the velcro. If you have weight pockets lock, make sure that close in the BCD, a high snap. Lace low may mean a bad connection. In any case, make sure the pockets out easily - but not too easily. Remove all knives and empty pockets. Independent BCD cleaning.
4. Soak in BCD in fresh water after each dive day. Large is best, but not crazy.
5. BCD Fill with water and air. Rinse the inside thoroughly. Shake vigorously with air and water in the bladder. Repeat at least twice.
6. Make sure the water flows through the inflation valve (BCD inflate with water and air and vacuum through inflation while maintaining the flexible valve low and deflation). Use a toothbrush to scrub around the rate of inflation and buttons of the index of deflation. Repeat at least twice.
7. Fill the air bladder and freshwater. Use drain valves to empty the bladder. Make sure fresh water is supplied through the valves. Remove and inspect the valves. Look for corrosion cell. Replace if rusted.
8. Inflate the bladder completely. Keep under water. Inspect the seams of the bladder, the air filtration. If the exhaust air carrying technical diving.
9. Hang dry. Do not lie in the concrete floor.
10. Once dry, inspect thoroughly. For spots of salt or dirt. If you find them, or repeat completely clean.
Consider using BCD McNett life as a cleaning agent.
For more information, consider a course computer specialist at the Academy Diving
About the Author:
PADI Master Instructor, NAUI Instructor Trainer, SDI Instructor Trainer, Technical Dive Instructor, DAN Instructor, SeaSigns Instructor Examniner
Article Source: ArticlesBase.com - Cleaning And Caring For Your Scuba Bcd
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