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
The most recent auctions for Bcd Buoyancy are listed below. If this page did not produce the Auction results you were looking for, conduct another search for Bcd Buoyancy, but be very specific. Use the exact brand and model you are looking for. Bcd Buoyancy Auction results are listed below, you can now search throught the results and find great low prices on Bcd Buoyancy.
 |
 Scuba Diving TUSA X Pert Tourer BC Buoyancy Compensator XS S BLK PINK BCD New US $51.00 |
 Sea Quest BCD Buoyancy Compensator size L excellent condition Fast Shipping US $55.00 |
 XLARGE Sherwood TORTUGA BC Scuba Diving BCD Buoyancy US $299.98 |
 Used Horse Collar Style BCD Blue Co2 Buoyancy Vest US $25.00 |
 MARES VECTOR EPIC BCD DIVER BUOYANCY COMPENSATOR US $225.00 |
 SCUBA PRO CLASSIC PLUS BC Size XL Buoyancy Compensator BCD GUC US $250.00 |
 Special Price Buoyancy Compenstor Weight Integrated BCD US $198.00 |
 SCUBA AIR HORN for BUOYANCY COMPENSATOR BCD QUICK CONNECT US $35.00 |
 seaQuest diva qd bcd womens buoyancy Compensation device M L ocean scuba vest US $41.00 |
 Sea Elite Hybrid Profiler Scuba Buoyancy Compensator BCD Size LG Large US $100.00 |
 Nearly New Sherwood Avid CQR2 Buoyancy Compensator Device BCD Large US $41.00 |
 CAM BAND BCD Cylinder Scuba Divers Buoyancy Jacket Band US $18.97 |
 SCUBA AIR HORN for BUOYANCY COMPENSATOR BCD SCUBAPRO SIZE QUICK CONNECT US $25.00 |
 Seaquest Malibu BCD BC Buoyancy Compensator size S mens small US $175.00 |
 BCD STORAGE TRAVEL BAG SCUBA DIVE DIVE GEAR Buoyancy Compensator US $19.99 |
 BCD FILLER HOSE SCUBA DIVE DIVE GEAR Buoyancy Compensator US $19.99 |
 Mares Hybrid She Dives Scuba Diving BCD Buoyancy Compensator LG US $399.96 |
 WOMENS SEAQUEST EVA BCD BUOYANCY COMPENSATOR MEDIUM NWT US $99.99 |
 NEW BCD Buoyancy Compensator SM WTINTERGRATED US $197.99 |
 NEW BCD Buoyancy Compensator XL WTINTERGRATED US $197.99 |
 NEW BCD Buoyancy Compensator MEDIUM WTINTERGRATED US $197.99 |
 NEW BCD Buoyancy Compensator LARGE WTINTERGRATED US $197.99 |
 NEW BCD Buoyancy Compensator 2X WTINTERGRATED US $197.99 |
 Sherwood Scuba Diving Freedom BCD Buoyancy Compensator Vest Size Large US $61.00 |
 Advantage Back inflate BCD Buoyancy Compensator size 2XL US $349.99 |
 Mares ICON Travel Buoyancy Compensator Scuba Diving Travel BCD XS US $551.34 |
 Mares ICON Travel Buoyancy Compensator Scuba Diving Travel BCD S US $551.34 |
 Mares ICON Travel Buoyancy Compensator Scuba Diving Travel BCD XL US $551.34 |
 Mares ALIIKAI Womens Travel Buoyancy Compensator Womens Travel BCD XXS US $299.72 |
 Mares ALIIKAI Womens Travel Buoyancy Compensator Womens Travel BCD XS US $299.72 |
 Mares ALIIKAI Womens Travel Buoyancy Compensator Womens Travel BCD S US $299.72 |
 Mares ALIIKAI Womens Travel Buoyancy Compensator Womens Travel BCD M US $299.72 |
 Mares ALIIKAI Womens Travel Buoyancy Compensator Womens Travel BCD L US $299.72 |
 Mares Kaila Ladies Scuba Buoyancy Compensator BCD Designed for Women XS US $551.40 |
 Mares Kaila Ladies Scuba Buoyancy Compensator BCD Designed for Women S US $551.40 |
 Mares Kaila Ladies Scuba Buoyancy Compensator BCD Designed for Women M US $551.40 |
 Mares Kaila Ladies Scuba Buoyancy Compensator BCD Designed for Women L US $551.40 |
 NEW OCEANIC BIOLITE SCUBA DIVING BUOYANCY COMPENSATOR BCD SIZE LARGE BC US $338.95 |
 Aeris Contour BCD Womens Contour Buoyancy Compensator L US $273.05 |
 Aeris Atmos LX BCD Hybrid Jacket Buoyancy Compensator Device S US $441.94 |
 NEW OCEANIC EXCURSION 2 BUOYANCY COMPENSATOR X LARGE SCUBA DIVING BCD BC US $375.00 |
 CRESSI AQUAPRO 5 BUOYANCY COMPENSATOR BC Size Medium SCUBA DIVING BCD US $175.00 |
 CRESSI AQUAPRO 5 BUOYANCY COMPENSATOR BC Size Small SCUBA DIVING BCD US $175.00 |
 Sea Quest BCD Buoyancy Compensator size XL excellent condition Fast Shipping US $55.00 |
 Sherwood Scuba Diving Freedom BCD Buoyancy Compensator Vest Size SMALL US $100.00 |
 Mares Kaila Scuba Diving BCD Buoyancy Compensator LG US $399.20 |
 SEAQUEST DIVA SMALL WOMENS BCD BUOYANCY COMPENSATION DEVICE VEST US $.99 |
 Scuba diving BCD inflator VALVE UNIT buoyancy compensator POWER INFLATION device US $31.60 |
 Oceanic Cabo BCD Scuba Diving Dive BC Size SM Buoyancy Compensator Small US $169.98 |
 Mares Dragon BCD Scuba Buoyancy Compensator US $499.00 |
 Mares Dragon AT BCD Scuba Buoyancy Compensator US $649.99 |
 Mares Prestige W MRS BCD Scuba Buoyancy vest US $449.99 |
 Repair Scuba Buoyancy Compensator Device BCD DIY Valve US $78.00 |
 Aeris 5 Oceans Buoyancy Compensator BCD XS US $395.00 |
 Aeris 5 Oceans Buoyancy Compensator BCD Small US $395.00 |
 Aeris 5 Oceans Buoyancy Compensator BCD Medium US $395.00 |
 Aeris 5 Oceans Buoyancy Compensator BCD Large US $395.00 |
 Aeris 5 Oceans Buoyancy Compensator BCD XL US $395.00 |
 US Divers Aqua Lung BCD Large NO RESERVE Buoyancy Compensator US $.99 |
 BCD Zeagle ESCAPE Scuba Dive Buoyancy BC Diving LG NEW US $399.98 |
 Scuba Diving Dive BCD BC Zeagle Weight integrated Buoyancy Compensator Travel US $9.00 |
 Scuba Diving Dive BCD BC AquaLung US Diver Buoyancy Compensator Vintage parts US $9.00 |
 NEW Mares Hybrid Dive Mens BCDBC Buoyancy Compensator Size XL US $470.99 |
 BCD TUSA PLATINA 3860 DIVING BUOYANCY COMPENSATOR scuba diving equipment XL US $379.95 |
 Seaquest BCD M Tusa Duo Octopus Inflator Scuba Diving Dive Buoyancy Compensator US $305.95 |
 SALE XL Cressi Aquapro 5 BCD Scuba Diving Dive Divers Buoyancy Compensator US $260.82 |
 Mares Aliikai Scuba Diving BCD Buoyancy Compensator LG US $399.20 |
 BCD NEW Zeagle RANGER Scuba Dive Buoyancy BC Diving LG US $699.98 |
 Genesis Cobra LD BCD scuba dive diving buoyancy compensator vest size Small US $199.98 |
 H2Odyssey Intrigue Scuba Dive Buoyancy Compensator BCD US $373.90 |
 SEAC AIRONE DIVING BCD VEST X LARGE XL BLUE BLACK SCUBA BUOYANCY DIVE NEW US $299.95 |
 SEAC AIRONE DIVING BCD VEST X SMALL XS BLUE BLACK SCUBA BUOYANCY DIVE NEW US $284.95 |
 Mares ICON Travel Buoyancy Compensator Scuba Diving Travel BCD US $498.95 |
 Bare BCD BlackJack Scuba Diving Buoyancy NEW MD US $439.96 |
 SEAC SUB MITO BUOYANCY COMPENSATOR SCUBA DIVE BCD SEAC SIZE MEDIUM M L US $333.00 |
 Mares Kaila Ladies Scuba Buoyancy Compensator BCD Designed for Women US $499.00 |
 Mares F Light BCD BC Scuba Diving Dive Buoyancy Jacket BCD Medium US $297.95 |
 Cressi AIR TRAVEL BCD Wings Buoyancy Jacket ALL SIZES US $458.32 |
 Cressi AIR TRAVEL BCD Wings Buoyancy Jacket LADIES US $458.32 |
|