Know your gear

Steel and aluminum are common cylinder materials. In the US, steel tanks have rounded bottoms whereas aluminum tanks are flat-bottomed. 

Steel tanks usually sink more (they are more negatively buoyant) than comparably sized aluminum tanks. This makes them popular with cold water divers, who don't have to wear as much lead when using a steel tank. Aluminum tanks are common in warm locations and as additional tanks for tec diving or as a backup gas supply because they are closer to neutrally buoyant. 

Check the shoulder markings (and bottom) for the capacity and service (fill) pressure in PSI or bar. 1 bar = 14.5 PSI  https://www.xsscuba.com/cylinder-markings . Tanks and pressure gauges in the US are usually rated in PSI.

Service pressures range from low pressure (LP) of ~2,400-2,640 PSI, to standard of ~3,000 PSI, to high pressure (HP) of ~3,500.  The most common aluminum tank, an 80 cubic foot capacity tank, is usually 3,000 PSI. HP steel cylinders are often 3,442 PSI. 

Note the capacity, often marked on the shoulder. In the US it is customary to express capacity in cubic feet of gas. 80 cubic foot aluminum tanks are the most common. During your dives, log the capacity of your tank, your starting and ending pressure, and your average depth (logged by your dive computer). This will allow you to calculate your gas consumption rate. About 0.5 cubic feet (at the surface) is typical for an adult male at rest. Knowing your consumption rate, you can calculate if the tank you've chosen for your dive has enough gas to complete your dive as planned.

Verify the tank has been hydrostatically tested, "hydro'd",  within the last 5 years. Hydro dates are stamped into the metal on the shoulder of the tank. For example:  03/21 would indicate a hydro test in March of 2021. Month and date will be separated by a special mark of the tester. Find the most recent date stamp. Don't use tanks with expired hydros.

Verify the tank has been visually inspected or"VIP'd" within the last year. The VIP checks for cracks, corrosion, and a functioning valve seal. This is indicated by a sticker, usually punched on the month, year, and date of inspection. Do not use it if it is out of date.

Check for any obvious signs of damage (giant dents, big rusty scratches, mangled valve threads, bent valve, etc.). Don't use if you suspect the tank or valve may no longer be structurally sound.

Check the tank markings to verify the gas mix. Most tanks without special markings are for air. A green and yellow VIP sticker or tank bands in the US may mean the tank is used for an oxygen-enriched air, "nitrox" mixture. The visual inspection sticker may have this information. Do not dive a tank marked for nitrox unless you have been trained to do so, or it has been tested in your presence  with a calibrated oxygen analyzer and contains a normal oxygen percentage (~20.9%). NEVER dive tanks containing nitrox or pure oxygen unless you have received appropriate training.  This can be fatal. Taking them beyond their rated maximum operating depth (which may be as shallow as 20 feet for pure oxygen) can result in convulsions and death.

Smell your gas to check for contamination before every dive. Gas can become contaminated if the filling compressor is not functioning properly, if their are problems with the filters, or if the air intake is contaminated by boat or other vehicle exhaust. Turn the valve gradually and gently until it is barely open and smell the gas coming out. It should smell like nothing. Do not dive a tank with any moldy, smoky, or gasoline type odors.

Check whether your tank valve is yoke, DIN, or a hybrid "pro valve". For yoke, the o-ring sits in valve and a screw is used to clamp the valve and regulator face together. For DIN the o-ring is retained in the regulator 1st stage and the 1st stage screws directly into a threaded tank valve. Pro valves are yoke and DIN. With the "din-sert" (DIN insert) inserted, they mate with yoke regulators. Remove the DIN-sert and it exposes threads that allow it to mate with a DIN regulator. Verify your tank (yoke) or regulator (DIN) has an o-ring in good condition. 

Ask for a tank that is a good fit for your stature and strength. Here in the Pacific Northwest, steel HP 100 (high pressure 100-cubic foot) and HP 80 tanks are common. HP 80 tanks are much lighter (9 lbs of dry land savings when full compared to an Alumninum 80 or an HP 100) and are significantly shorter. They better fit people with shorter torsos and are easier to carry due to their lighter weight. Most women, adolescents, and shorter men will be more comfortable in an HP 80 than an HP 100. If you are a tall, strong person who goes through air quickly, you might also ask for a larger tank (bigger than an HP 100).

When starting and ending dives, always fully open or fully close your tank valve. A tank that is not fully open can result in an inadequate air flow at depth. An old practice was to open the valve fully then turn it back a quarter turn. Do not do that. Partially open (or partially closed) valves have contributed to several accidents and fatalities. 

Your BC uses air to adjust the volume of water you displace - which allows you to achieve neutral bouyancy - neither sinking nor floating - at all times during your dive. At the surface, before and after diving, they should always be inflated to keep you floating with your head out of the water so you can breathe easily. 

Check that your BC fits you. You should be able to adjust it to be snug, but not constricting. 

Locate all of the valves for deflating your BC and practice using them by feel / muscle memory when you dive and during your predive safety check. Know when to use which deflator. For example, since air rises in water, hip dump valves allow you to vent gas when you are horizontal or head-down in the water. 

Often, jacket-style BCs have 4 deflator mechanisms. (1) Press the button at the end of the inflator hose. (2) Pull the inflator hose to vent from the left shoulder dump. (3) Pull the string attached to the right shoulder to vent from the right shoulder. (4) Pull the string located near your hip/kidney/butt to the left or right side of the tank. 

Check that your inflator hose and valves are securely attached by twisting them clockwise to make sure they are snug. They often screw on to a fitting welded into the BC. They can come loose. If this happens during a dive, your BC may be unable to maintain sufficent air for your to establish neutral buoyancy - which can increase your risk of an uncontrollable descent, or make it hard to ascend to end your dive. 

Check that you can inflate your BC with both the power inflator (low pressure inflator hose) and the oral inflator. If it does not fit you properly, it may be difficult to reach the oral inflate mouthpiece to your mouth. Adjust or get a new BC if necessary.

Verify that your BC holds gas and does not leak when inflated. 

Check for wear and verify function of all buckles, straps, and releases.

Check the integrated weight system (if present) for your BC. Know how to secure weight so it doesn't come loose during a dive. Know how to operate the quick release so you can drop your weight if you have a problem staying buoyant at the surface. Many BCs have weight pockets that slide in and out. Verify the max weight capacity of your pockets and do not exceed it.

Consider the lift capacity of your BC. The lift capacity measures how much negatively buoyant weight it can offset. You can look this up online or it may be printed on your BC. Many BCs designed for warm water diving have a fairly small lift capacity. Check that when loaded with weight, and a full tank (which is negatively buoyant) your BC can still float. If not, get a BC with a higher lift capacity or move more weight to a different sytemt (weight belt or harness). If your BC cannot float when fully inflated it can contribute to problems getting in and out of boats, or in the event of an issue that requires you to remove your scuba kit at the surface.

Consider a backplate and wing style BC. Most divers learn in jacket-style BCs, but backplate and wing configurations (BP&W) are becoming more popular with recreational divers. This BC style is standard if you progress to tec diving. Typically, a steel or aluminum backplate and nylon webbing harness form the structure of a BP&W. An air bladder called a "wing" is screwed on to the back of the backplate. The wing will have a standard BC inflator hose.  BP&W style BCs move some weight onto your back (in the form of the metal plate) which puts it near your center of gravity and distributed nicely between shoulders and your lower back. This can make them more comfortable and stable - particularly in cold water where we carry a lot of weight. BP&Ws locate your air bladder above you when you are swimming - which makes it easy to stay in horizontal trim (but a bit harder to stay vertical at the surface). BP&W systems are modular. If a component fails you can switch out the broken bit and keep diving instead of having to replace your entire BC. They are customizable - so you can move your D-rings and other components to where you need them. Many experienced divers choose to carry a redundant air supply for deeper dives. It is easier to carry such a "pony bottle" (clipped to the left chest and hip D-rings) with a backplate and wing than it is with many jacket-style BCs.

Service your BC inflator mechanism annually or as recommended by the manufacturer or if it begins to leak or stick. Often, replacing it with a new one annually can be easier and cheaper than servicing it. An inflator valve that sticks open can suddenly and rapidly fully inflate your BC leading to a dangerous uncontrolled, buoyant ascent. Practice disconnecting your BC inflator hose while swimming down and dumping air in case you ever have to respond to this problem on a dive. 

Consider a bright color especially if you dive in low-visibility water like we do here in the Pacific Northwest. 

The 1st stage regulator reduces tank "high pressure" to an intermediate "low" pressure of ~125-150 PSI. This is  delivered via low-pressure (usually labeled "LP") ports in the regulator to the hoses for 2nd stages and BC/drysuit inflators. It also has tiny holes in the "high-pressure" (HP) ports that allow tank pressure to pass directly to your SPG or air-integrated (AI) transmitter so you can track remaining tank pressure.  

Consider a DIN regulator. If purchasing your own regulator for local use, you may prefer DIN. Because of the o-ring placement and deep, threaded connection between the valves themselves, they are not prone to blowing out an o-ring which can lead to rapid gas loss on a yoke regulator. DIN is considered a safer and more secure connection. DIN regulators are required if you progress to tec diving. DIN regulators can use an adaptor to connect to a yoke tank, but the reverse is not true. 

Consider the regulator's rated operating temperature. Many regulators designed for warm-water are only rated for temperatures above 50 degrees Farenheit (50 F / 10 C) and the manufacturer states not to use them below that temperature due to an increased risk of a free flow. If you will be diving here locally, our water is frequently colder than 50 F. An environmentally-sealed regulator rated for colder temperatures may reduce your risk of a free flow. 

Fasten your first stage to the tank valve finger-tight only. Don't tighten with your fist or it will be hard to remove.

Check your regulator 1st stage (DIN) or tank valve (yoke) for an o-ring. Replace the o-ring if worn or leaking.

Check that the 1st stage filter (looks like a metal sponge) is clean and free of any significant corrosion or debris.

Service your regulator acccording to manufacturer instructions. Most regulators are serviced annually or every two years, or more often with heavy use. 

Negative pressure test: breathe out through the mouthpiece (to clear dust/sand), then breathe in to check for leaks in the exhaust valves. Do this  withthe  dust cap in place. Leaking exhaust valves can lead to your regulator breathing "wet". 

Inspect mouthpiece:  Ensure cable tie is present and secure. Check for rips in mouthpiece, replace if needed.  An unsecured or damaged mouthpiece can lead to breathing water instead of air. 

Check for effort of breathing. It should breathe easily when you inhale and exhale. Some regulators are adjustable. If it hard to breathe, have it serviced before diving it.

Check for freeflow. The regulator should not leak air when you are not inhaling. 

Check the hose. It should have no significant nicks, cuts, cracks, signs of aging, corrosion at crimp, or leaks. 

Replace hoses every 5 years or if they show signifcant signs of wear to prevent failures which could lead to loss of breathing gas at depth. 

Check underwater for leaks (bubbles) at beginning of every dive. Your buddy may be better able to spot these than you. Check each other. 

Service your regulator annually or as recommended by manufacturer (some are 2 years)

Consider where  you will clip or stow your alternate 2nd stage or "octo".  It should be somewhere in the triangle formed by your chin and outer edges of your ribs. 

Consider a primary-donate, long-hose configuration.  This gear configuration gives you seven feet instead of three feet of hose for sharing air. This makes sharing air more comfortable by allowing you and your buddy to spread out a bit - instead of having to be in each other's face. It may also make it less likely that you accidentally dislodge the regulator from your buddy (because of tight quarters).  Panicked out-of-air divers are reported to often grab your primary regulator anyway - if this happens, this gear configuration keeps your alternate backup regulator where you can always easily retreive it, just below your chin on your necklace. This configuration is typically required for tec diving.

To connect the quick disconnect (QD) fitting - push the hose onto the male valve fitting while pulling the female flange backwards toward the 1st stage end of the hose. The same process will allow you to disconnect - push the hose into the fitting while pulling the flange away from the fitting, then pull the hose off the fitting once you feel it disconnect. Connecting and disconnecting is  easier when there is no pressure in the line. If the line is pressurized, pushing the inflator button while disconnecting may  help you to disconnect. 

Check if the metal valve connection is easy or difficult. If the valve stem or the hose end of the quick disconnect are soiled or worn, they may need to be cleaned or replaced. 

Practice disconnecting quickly by feel, while swimming down and venting from your hip dump in event of a stuck inflator which could lead to uncontrolled buoyant ascent. 

Check the hose for significant nicks, cuts, cracks, or signs of wear and replace if damaged.

Replace the hose every 5 years even if no signs of wear are evident to avoid hose failure and sudden loss of gas at depth. 

Check that the gauge reads reads 0 PSI or 0 bar when not pressurized. If it does not, replace it. Do not dive it. 

When turning on your tank valve, point the plastic gauge face away from others (against your tank or the ground is a good practice) in case the gauge mechanism breaks and causes the gauge face to shatter/break (very rare). 

Verify tank pressure is full or nearly full before diving. It should roughly match your service pressure. Avoid overfilling your tanks which can lead to premature metal fatigue.

As part of pre-dive safety check, test breathe your 2nd stage regulators while watching the pressure on your gauge or air-integrated computer to verify air is flowing without restriction and tank valve is fully on. The pressure should drop minimally or not at all when you breathe.

Consider where you will clip or stow SPG so it does not dangle

Replace your SPG high-pressure hose every 5 years  or if it shows significant signs of wear such as deep nicks, cuts, scratches or cracking. 

Consider an air-integrated pressure transmitter (and computer to receive the signal) if buying your own gear. It allows you track your gas pressure on your computer instead of requiring an SPG and hose. Transmitters may be more reliable than analog pressure gauges and may allow you to eliminate a hose from your kit increasing streamlining and decreasing failure points.

Verify it turns on and battery level is sufficient to complete the dive

Verify it is set to the correct gas. If you are diving air it should indicate "air" or "21%" FO2 (fraction oxygen) depending on the manufacturer. 

Verify time and date are correct. This lets you track the time of day underwater (e.g. "return to the boat by 11 am") and log your dives accurately. 

Read the manual before diving it. In particular, know how to read depth, dive time, no decompression time remaining (often "no deco" or "NDL" - no decompression limit), emergency decompression stop instructions, and safety stop instructions.

Set your computer to match your intended dive plan. Consider adjusting safety stop duration (many allow you to set for 5 minutes for more conservatism), setting a max depth alarm, a low deco alarm, or other custom alerts if supported by your computer. 

When purchasing, consider the type of diving you intend to do - do you need a multigas computer? Almost all computers will calculate nitrox and air dives on a single tank. If you have trouble with close vision, consider screen size and font size. Will  the computer you dive be the same as your buddies? If not, be sure to familiarize yourself with each other's computers. Is it rechargeable or easy to change the battery? How customizable is the computer? Can it alert you to issues (e.g. exceed planned depth) visually, with beeps, and/or via vibration? Does it come with a compass?

Air integration (AI) is an increasingly common feature that allows you to track your tank pressure on your computer. AI computers can usually estimate gas time remaining based on your consumption rate, remaining pressure, and depth. Diving with an AI computer may allow you to dive without an analog SPG and hose - increasing your streamlining. Not all computers support air integration. Air integration always requires a transmitter that is screwed into one of your 1st stage high pressure (HP) ports.

Visibility can be limited underwater, so a compass is standard dive equipment.

Verify that you have one and know how to use it before each dive. 

Many computers and even some underwater cameras (e.g. the Olympus TG-5, TG-6) have built-in electronic compasses. You may choose to use these instead of an analog version. 

weight integrated BC

trim weights (BC and/or cyclinder band)

weight belt

weight harness - keeps from falling off hips

cold water considerations - learn more

hard, soft

threaded, lead exposure

backplate, v-weight

drysuit best here to stay warm enough

semidry wetsuit is next warmest

regular wetuits are usually uncoformtably cold in our local waters

for additional warmth, use a drysuit with dry gloves, a thick (10-11 mm) hood, and additional undergarment layers

heated vests also an option 

Consider a bright color especially if you dive in low-visibility water like we do here in the Pacific Northwest. 

consider stainless steel spring straps - durable, no adjustment to make when you take them on and off, rarely fail

fin style - will they work well for all types of finning including frog kick, helicopter turns, and back finning/back kicking?

locally we use open heel fins that can fit over thick wetsuit or drysuit boots

get scuba fins, not snorkel fins

try your fins on with the boots you intend to buy for your wetsuit or drysuit

Consider a bright color especially if you dive in low-visibility water like we do here in the Pacific Northwest. 

appropriate fit most important, should not leak if you inhale, try with regulator in mouth or snorkel

shave moustache or stubble to reduce leakage under nose

can get prescription lenses, or reader inserts

SMB/DSMB or other visual

whistle or other auditory

TIP: buy and take with you, small, travel easily

lights - 2+ for night diving, standard here even in daytime

cutting tools - belt cutter, EMT shears, dive knife - for fishing line or similar entanglements or to cut diver out of gear for rescue

best stowed in a pocket or clipped onto your BCD

O2 kit - standard 1st aid

way to reach emergency services - cell phone to call 911, marine radio or satellite phone if out of cell range

Emergency Action Plan - have a plan for what to do in an event of an emergency, know the phone numbers for DAN (Divers Alert Network) and local emergency services (e.g. 911). This can be as simple as "we will call 911" if diving from an urban area. Remote areas may require more planning/equipment.

AED - heart attacks are a leading cause of diver injury and death, particularly among older divers. Access to an AED may save someone's life. Know where the closest one is. Many local dive sites have AEDs nearby.