The Five Basic Parts of a Scuba Diving Regulator

Oceania, Micronesia, Yap, Diver with grey reef sharks, Carcharhinus amblyrhynchos
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 A scuba diving regulator is the piece of equipment that enables a diver to breathe from a scuba tank. The regulator is so named because it regulates the pressure of the air a diver breathes. The compressed air inside a scuba tank is at an extremely high pressure, which could injure a diver who tries to breathe directly from the tank, and the regulator is necessary to reduce the pressure of the compressed air to a pressure the diver can breathe.

To accomplish this, a regulator reduces air pressure in two steps, or stages--first, from the pressure in the tank to an intermediate pressure; and second, from the intermediate pressure to a pressure that the divers can safely breathe. In it's most basic form, a scuba regulator consists of two parts: a mechanism that accomplishes the first stage of pressure reduction (called a first stage) and a mechanism that accomplishes the second stage of pressure reduction (called a second stage). However, contemporary scuba diving regulators usually incorporate a variety of additional accessories.

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Introduction

Zeagle Regulator Photo by Natalie L Gibb
Parts of a Scuba Diving Regulator The five basic parts of a scuba diving regulator for use in the open water: 1. first stage 2. primary second stage 3. alternate second stage 4. submersible pressure gauge and gauge console 5. low pressure inflator hose. Natalie L Gibb

Five basic parts are usually included in a standard open water scuba diving regulator.

1. First Stage
The regulator first stage attaches the regulator to the scuba tank. Remember, a diving regulator reduces the air from the scuba tank in stages as it travels from the tank to the diver. The first stage of the regulator is named for its function: it accomplishes the first stage of pressure reduction by reducing the high-pressure air in the tank to an intermediate pressure. The air travels through the low pressure (LP) regulator hoses at this intermediate pressure; however, the air at this intermediate pressure is still at too high to be breathed directly, and requires further reduction.

2. Primary Second Stage
The part of the regulator that a diver puts in his mouth is called the second stage. The regulator second stage is attached to the first stage by a low-pressure hose. The name “second stage” comes from this part's function as the second stage of pressure reduction. It takes the intermediate pressure air from the regulator hose and reduces it to ambient pressure--a pressure equivalent to the air or water pressure surrounding a diver, allowing a diver to breathe from the second stage safely.

The primary second stage is one of two second stages attached to a standard open water regulator, and it is this one that a diver normally breathes from during a dive.

3. Alternate Second Stage
The alternate second stage (also know as an alternate air source, buddy regulator, or octopus) does the exact same thing as the primary second stage: it reduces intermediate air pressure supplied by a low-pressure hose to an ambient air pressure that a diver can breathe.

The alternate second stage is a back-up, that ordinarily is not used. It enables a diver to share air from his tank with a second diver in case of an out-of-air emergency. Alternate second stages are usually bright colors, such as neon yellow, which allows them to be quickly located. As diver education and safety procedures have evolved, alternate second stages have become standard scuba diving safety gear, allowing any diver to breathe from any other diver's tank.

4. Submersible Pressure Gauge and Gauge Console
The submersible pressure gauge (also called a pressure gauge or SPG) allows a diver to monitor the amount of air in his scuba tank so that he doesn't run out of air underwater. The pressure gauge is connected to the regulator first stage by a high-pressure hose (HP hose) that feeds high-pressure air from the tank directly to the pressure gauge. Frequently, the console containing the pressure gauge also holds a variety of other gauges, such as a depth gauge, compass, or dive computer.

5. Low-Pressure Inflator Hose
This low-pressure hose carries intermediate-pressure air from the regulator first stage to the Buoyancy Compensator's (BC) inflator. This allows divers to add air to the BC from the tank at the touch of the button.

Let's look at each of these five components in greater detail. 

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First Stage

Parts of a Scuba Diving Regulator The basic parts of a regulator first stage: 1. first stage body 2. yoke 3. yoke screw 4. dust cap 5. port/port plug. Natalie L Gibb

A scuba diving regulator first stage is the part of the regulator that accomplishes the first stage of pressure reduction, reducing the high-pressure tank air to an intermediate pressure. An open-water-style regulator first stage usually connects to four hoses--three that transport intermediate-pressure air to second stages and the buoyancy compensator's (BC) inflator, and one that allows high-pressure air to flow directly from the tank to the submersible pressure gauge.

1. First Stage Body
This metal cylinder contains the mechanisms that reduce the high-pressure air in the scuba tank to an intermediate pressure. High-pressure air flows in one side of the first stage body, undergoes pressure reduction, and then flows out through the low-pressure hoses.

2. Yoke
The regulator first stage body is held against the scuba tank's valve through one of two methods: a yoke or a DIN fitting.Learn more about the difference between DIN and yoke regulators. This diagram illustrates a yoke fitting, also called an international fitting. The “yoke” is the metal oval that fits over the tank valve to hold the regulator in place.

3. Yoke Screw
The regulator's yoke is equipped with a yoke screw--a metal screw that runs through the regulator yoke and tightens the regulator first stage body onto the tank. To tighten the yoke screw, the diver turns the black, plastic handle attached to the screw.

4. Dust Cap
It is extremely important that no water enters the regulator first stage body. When the first stage body is tightened onto a tank, it creates a water-tight seal to the tank valve. However, when the first stage body is disconnected from the tank, it is possible for water to enter the opening in the first stage, through which air passes from the tank to the regulator. The dust cap is a rubber cap that can be placed over the regulator first stage opening and tightened down using the regulator yoke screw. This seals closed the opening on the first stage.

5. Port/ Port Plug
Regulator first stage bodies have multiple openings, or ports, that regulator hoses can be screwed into. Usually, regulators have more ports than the standard number of hoses, which allows divers to position their hoses in a variety of configurations. These openings are called ports, and the plugs that close the regulator ports when they are not in use are called port plugs.

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Primary Second Stage

Regulator second stage diagram by Natalie L Gibb
Parts of a Scuba Diving Regulator Parts of a regulator second stage: 1. purge button 2. ease of breathing adjustment 3. exhaust valve 4. mouthpiece. Natalie L Gibb

The regulator second stage is the part of the scuba diving regulator that a diver actually breathes from. The function of the second stage is to reduce intermediate-pressure air traveling through a regulator hose to an ambient pressure (the pressure of the surrounding water) that a diver can breathe safely. A primary second stage is one of two second stages on a standard open-water-style regulator. Unless there is an emergency, a diver breathes from this primary second stage during a dive.

1. Purge Button
The purge button is located on the face of the regulator second stage. The purpose of the purge button is to flood the second stage with air, forcing water out of the second stage. Divers use the purge button when the second stage has been allowed to fill with water--for example, when a diver removes the regulator from his mouth during the regulator recovery skill.

2. Ease of Breathing Adjustment
Most regulators have a lever or knob that allows divers to adjust breathing resistance. This feature helps to prevent regulator free flow (a state when air flows rapidly out of the regulator second stage without the diver breathing from it), which typically occurs when the breathing resistance has been lowered too much. A free flow can quickly empty a tank.

Many second stage adjustments have a setting labeled "pre-dive" to help prevent free flow at the surface, and one labeled "dive" for easy breathing once underwater. As a diver descends, he can adjust the ease of breathing to compensate for the increased difficulty of breathing as he descends.

3. Exhaust Valve
The second stage exhaust valve is the plastic unit that channels exhaled air bubbles away from a diver's face. The exhaust valve is usually located below the regulator's mouthpiece to channel air down and to the sides. This helps to keep a diver's field of vision clear of bubbles.

4. Mouthpiece
The mouthpiece is the part of the regulator that a diver bites down on. High quality mouthpieces are made of silicon or soft rubber (not plastic) and come in a variety of shapes and sizes to fit divers' mouths. Mouthpieces are removable and replaceable. A diver should check to make sure that his mouthpiece is secured to the regulator second stage with a zip tie or cable tie to ensure that it does not slide off during a dive.

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Alternate Second Stage

Scuba Octopus Diagram by Natalie L Gibb
Parts of a Scuba Diving Regulator Parts of an alternate second stage: 1. mouthpiece 2. low pressure hose 3. purge button 4. ease of breathing adjustment. Natalie L Gibb

An alternate second stage (also called an alternate air source, buddy regulator, or octopus) does exactly the same thing as a primary second stage. The alternate second stage is not intended to be used except in the case of an out-of-air emergency. A diver with an alternate second stage can allow an out-of-air diver to breathe from his tank without putting himself at risk.

1. Mouthpiece
The mouthpiece is the part of the regulator second stage that a diver bites down on. Alternate second stage mouthpieces should be a standard size to fit any diver's mouth--not a custom mouthpiece. The idea is that any diver should be able to use the mouthpiece in an emergency.

2. Low-Pressure Hose
Low-pressure hoses (LP hoses) transport air from a regulator first stage to its second stages. An alternate second stage's LP hose is usually longer than the LP hose attached to the primary second stage. This extra length makes it easy for an out-of-air to use an alternate second stage attached to a tank he is not wearing. The LP Hose attached to an alternate second stage is frequently a bright color, such as yellow, to make it easy to see.

3. Purge Button
The purge button on the alternate second stage has the same function as a purge button on the primary second stage--to remove water that has entered the second stage. Alternate second stage purge buttons are usually brightly colored--this one is neon yellow. The bright color makes it easy for an out-of-air diver to locate the alternate second stage in an emergency. In general, the alternate second stage should be attached to the Buoyancy Compensator (BC) or diver somewhere between the bottom of the diver's chin and the lower corners of his rib cage.

4. Ease of Breathing Adjustment
Just like the ease of breathing adjustment on a primary second stage, the ease of breathing adjustment on an alternate second stage can be used to increase or decrease breathing resistance during a dive. If an ease of breathing adjustment is present, a diver should adjust it so that the breathing resistance of the alternate second stage is increased. The diver should also turn any pre-dive/ dive adjustment to "pre-dive." The regulator will still work if needed, but this adjustment will ensure that the alternate will not free-flow during the dive.

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Low-Pressure Inflator Hose

Low Pressure Hose Diagram by Natalie L Gibb
Parts of a Scuba Diving Regulator Parts of a low pressure inflator hose: 1. sleeve 2. attachment opening. Natalie L Gibb

The low-pressure inflator hose connects a regulator first stage to a buoyancy compensator's (BC) inflation mechanism, allowing divers to add air to the BC at the touch of a button.

1. Sleeve
The metallic sleeve encircling the outside of the low-pressure inflator hose's connection mechanism slides back towards to the hose. This sleeve must be held back to connect the hose to the BC inflator mechanism. Sleeves are usually textured to make them easier to grasp underwater. Divers planning on diving in cold water or with gloves should look for sleeves with well-defined, raised ridges that make them very easy to hold on to.

2. Attachment Opening
A diver attaches his BC's inflator mechanism to a low-pressure inflator hose by inserting the BC inflator connection into the hose's opening while holding back its sleeve. Low-pressure inflator hose attachment openings come in different sizes. Divers need to be sure that their inflator hose attachment will fit on to the BC inflator they plan to use.

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Submersible Pressure Gauge and Console

Console diagram by Natalie L Gibb
Parts of a Scuba Diving Regulator Parts of a diving gauge console: 1. depth gauge 2. submersible pressure gauge. Natalie L Gibb

The submersible pressure gauge (SPG, pressure gauge, or air gauge) is the gauge a diver uses to monitor the amount of air remaining in his scuba tank. It is absolutely essential in diving, for it allows divers to avoid running out of air underwater. A submersible pressure gauge is frequently grouped together with other gauges on a ​console. Some of the common gauges found in a console are depth gauges, dive computers and compasses.

1. Depth Gauge
A depth gauge has two needles to monitor two different things. A black needle indicates a diver's current depth. A second, in this case red, needle indicates the maximum depth a diver reaches on a given dive. The needle that indicates a dive's maximum depth needs to be reset at the beginning of each dive.

The maximum depth needle is useful when logging dives. It is also a good idea to glance at it when ascending from a dive to confirm that the planned maximum depth has not been exceeded. Depth gauges may be in units of feet or meters. (The gauge shown above is in meters.) Most depth gauges have standard safety stop depths indicated by red lettering, making it easy for a diver to remember his safety stop. The gauge shown above has the standard safety stop depth indicated by red lines between 3 and 6 meters.

2. Submersible Pressure Gauge
The submersible pressure gauge (SPG) indicates the amount of air pressure in a scuba tank. The units of pressure may be given in bar (metric), or in psi (pounds per a square inch, imperial). A standard, aluminum 80-cubic-foot tank is full at 3000 psi or 200 bar.

Different tanks styles may be full at different pressure ratings. Most pressure gauges indicate a reserve pressure, usually beginning somewhere around 50 bar or 700 psi, in red. The reserve pressure is the amount of air pressure with which a diver should begin his ascent to avoid running out of air underwater. Be warned:  this “red zone” does not indicated a good reserve pressure for every dive, and it is important to take the dive profile and plan into account when deciding on a proper reserve pressure for a dive.