Whether you are just starting to scuba dive, considering signing up for a scuba course, or need a quick refresher, this post will provide you with a comprehensive list of terms and acronyms used in relation to scuba diving equipment.
You can use this post as a reference guide before starting a scuba diving course or going on a scuba holiday.
If you are studying for your PADI Open Water Instructor Development Course, you can use the list below as flashcards. It contains all the terms you need to know for your Instructor Development Course and PADI Instructor Exam.
You might also be interested in all the definitions related to the Physics of scuba diving.
If you are studying for your PADI Open Water Diver COurse, you might also be interested in the following:
- PADI OWD Section 1 Knowledge Review Answers Explained
- PADI OWD Section 2 Knowledge Review Answers Explained
- PADI OWD Section 3 Knowledge Review Answers Explained
- PADI OWD Section 4 Knowledge Review Answers Explained
- PADI OWD Section 5 Knowledge Review Answers Explained
BCD
In scuba diving, BCD is the acronym for Buoyancy Compensation Device, or Buoyancy Control Device. This is the jacket that is connected to a scuba tank and is used to keep divers positively buoyant at the surface and negatively buoyant underwater. In some cases, BCD can also refer to a wing and backplate (or harness), which are an alternative to the classic jacket-style compensation device.
Scuba Regulator
In scuba diving, a regulator is composed of a first stage, second stage, emergency second stage and SPG. The second stage and emergency second stage are connected to the first stage via low pressure hoses, whereas the SPG is connected to the first stage via a high-pressure hose.
Yoke Valve/ Regulator
A Yoke Valve in scuba diving looks more like a clamp. It is used to connect the scuba regulator to the scuba cylinder. It is mostly used in recreational diving as it is considered less appropriate than a DIN valve. In a yoke valve, the O-ring is on the tank rather than on the valve itself.
DIN Valve/Regulator
As opposed to a Yoke Valve, a DIN valve is screwed into the scuba cylinder’s threaded valve. It is used mostly in cold water diving and by technical divers as it is considered safer in extreme water conditions than a yoke valve. In a DIN valve, the O-ring is on the regulator and encased deep inside the valve itself.
First Stage
The fundamental function of a first stage in a scuba diving regulator is to reduce the high pressure delivered by the cylinder to an intermediate pressure.
Piston First Stage
A piston first stage converts high pressure to intermediate pressure and delivers gas at a constant intermediate pressure to the second stage by using a sliding metallic piston that adapts to changes in water conditions, diver’s breathing needs and depth.
Diaphragm First Stage
A diaphragm first stage converts high pressure to intermediate pressure and delivers gas at a constant intermediate pressure to the second stage by using a flexible diaphragm that adapts to changes in water conditions, diver’s breathing needs and depth.
Balanced First Stage
A balanced scuba regulator has a larger orifice allowing a greater air flow from the scuba tank to the regulator and accessories. It is more fit to provide air when several accessories are being used and it is better than an unbalanced regulator in supplying air to two divers.
Second Stage
A second stage in scuba diving is designed to provide air to a diver on demand when they inhale. Air flows from the first stage to the second stage at an intermediate pressure above ambient pressure. The second stage reduces this to ambient pressure.
Octopus
In scuba diving, octopus refers to the emergency second stage. In most cases (but not always), an octopus is identifiable by its colour: both the second stage and the low-pressure hose are yellow.
Open Circuit Scuba
Open circuit scuba systems are the most common type of recreational diving scuba equipment. They are easy to use and maintain and vent exhaled gases directly into the water. The term “open circuit” refers to the fact that air is released directly into the water.
Rebreather
As opposed to an open circuit scuba system, a rebreather recycles usable gasses instead of allowing them to be wasted in the water. Rebreathers are also referred to as closed circuit scuba systems.
3AL
You might come across such marking in a scuba tank. 3AL designates the type of metal used to construct a scuba tank. In particular, 3AL is the U.S. specification code for 3-gauge aluminium.
(+) designation
Whenever you observe a (+) designation on scuba diving tanks, it means they can be overfilled to 10% beyond their working pressure.
Burst disk
A burst disk is a small disk installed in scuba tanks which prevents them from rupturing due to over pressurization. The burst disk is installed in the tank valve and is designed to rupture when the tank pressure rises above about 140% of the tank’s rated pressure.
Demand Valve
A demand valve in a scuba diving regulator, refers to a valve that will provide air only upon inhalation.
Fail Safe
Fail safe refers to a scuba regulator’s tendency to free-flow because of the use of a downstream valve in the second stage.
Environmental Seal
An environmental seal in a scuba regulator first stage operates by not allowing water to directly contact the first stage piston or diaphragm.
Submersible Pressure Gauge (SPG)
A submersible pressure gauge or SPG is used to measure how much breathing gas a diver has left in his cylinder at any time.
SMB
SMB stands for Surface Marker Buoy. SMBs are commonly used by scuba divers as a surface signalling device to be seen either by their own dive boat or by boats passing by. An SMB can also be used in case of emergencies to signal a distressed diver.
DSMB
DSMB stands for Delayed Surface Marker Buoy. As opposed to SMB, the DSMB can be deployed from below the surface. Scuba divers commonly deploy DSMBs while doing their safety stop. A DSMB is part of the equipment every diver should have. Check out my list of recommended gear and my guide on how to choose the right DSMB.
Capillary Depth Gauge
A capillary depth gauge is a simple piece of clear tubing, sealed only at one end, with depth increments indicated according to where the water column rests based on Boyle’s Law. Capillary depth gauges are inexpensive and reliable although difficult to read accurately much deeper than 10 meters/ 30 feet.
