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The high pressure in the scuba tank must be delivered to the diver at the same pressure as that in the surrounding water. The regulator does this. It makes little difference what brand is being used. They are all reliable, efficient, and have an extremely low failure rate. There would be many damaging lawsuits if that were not true.
In the modern single-hose regulator there are two stages. The first stage is that part that attaches to the tank. The primary second stage has the mouthpiece that goes in the diver's mouth. The air entering the first stage from the tank might be 3000 psi. The air leaving the first stage through the hose to the second stage will be about 140 psi. The air entering the diver's mouth from the mouthpiece will be at the ambient water pressure. (Note: "ambient" means surrounding.)
Once the regulator is attached to the tank and the tank is turned on, there is no noticeable air flow. Air is not wasted when the diver isn't breathing. As the diver inhales from the mouthpiece, the pressure is lowered inside the second stage. Water on the outside of the diver's mouth pushes a diaphragm in. That is connected to a lever that opens the valve to the air in the hose coming from the first stage. As the 140 psi air pressure is lowered, another valve opens in the first stage and the air from the tank enters. When the diver exhales the process reverses and the air flow is shut off.
Sometimes a regulator, that is not in the diver's mouth, is placed in the water with the mouthpiece facing up. The water at the lower point has greater pressure and pushes the diaphragm in just as it does when the diver inhales. The regulator starts to quickly release air by itself. To stop the air flow it is necessary to turn it over so the mouthpiece is pointing downward. After the flow stops the regulator may be released with no further "bleeding."
Although there should be no leaks with most regulators, a minor leak is not something that should cause grave concern. (Some regulators are designed to leak small amounts of air in order to keep water from entering the regulator's interior.) A leak that has a barely audible hiss, although it should be repaired, will not subtract much from the dive time. To illustrate this: If you let the air that is leaking flow into the bottom of a water-filled cubic foot box, so that as the air went in the box the water would come out, that time it took to fill the box would roughly amount to about 1 minute of dive time.
Breathing underwater is about the same as breathing in the atmosphere. The inhale should be slightly deeper, followed by the exhale. There should be no pause between the two. It is important to keep the lungs well ventilated when ascending: DO NOT hold your breath when you rise in the water or serious, and possibly fatal, lung damage could occur.
If the regulator is put in the mouth underwater it will be necessary to blow the water out of it prior to breathing in. A simple exhale will accomplish that. A regulator should never be placed in the mouth upside down. When that happens the exhaust port is above the mouthpiece making it impossible to get the water out of the interior. The inhale will contain mostly water resulting in a possible drowning! This is especially important to remember when your regulator is handed to a buddy.
On the rare occasion some water may leak into the second stage. There are three main reasons for this:
Throwing up underwater is rare. That is fortunate. Thinking about the process leads one to many questions. Should you throw up into the regulator? Should you take the regulator out and risk drowning on the inhalation? Will the diver remain under control during the process? Don't dive if there is a feeling of nausea. If the diver feels they are about to throw up try to move safety to the surface. If it has to be done under water, I think the best procedure would be to throw up into the regulator, replace the regulator with the alternate air and resume breathing. Clean out the primary second stage by shaking and pressing the purge button, and then return that to the mouth. Be aware: This author has never put this to the test. I am aware of a few divers successfully doing it.
The proper procedure to remove a regulator from the tank is:
Shut off the air from the tank.
Purge the air from the regulator by pushing the secondary purge button. This will prevent the loud and damaging pop to the tank's O ring, and will make removal of the regulator easier.
Disconnect the hose from the BCD.
Carefully remove the regulator from the tank - before doing this be sure the pressure has been removed!
Turn the tank on slowly so a stream of air is flowing and then hold the dust cover (yolk cap) in it. That will blow and dry the water from the dust cover. Prevent the spraying water from entering the sintered filter.
Place the dust cover on the opening to the regulator and turn the tank knob to hold it in place.
If the regulator has been used in salt or contaminated water it should be rinsed with fresh water. During the rinse the purge buttons must not be depressed, and the dust cover must be in place or water may get into the regulator's interior.
If part of the regulator allows one to keep the the purge button(s) depressed during storage it should not be done. At one time this technique was practiced to keep pressure off the low-pressure seat(s) prolonging their life. After servicing hundreds of regulators it was discovered there was little or no difference to the life of the seat. Keeping the purge button depressed did dramatically increase the risk of having cantaminates enter the seconday hoses. In addition Divemasters unfamiliar with depressed purge may assume the stage is leaking and take unnecessary corrective measures.
Hang the regulator up to dry using all the hoses.
There are high and low-pressure ports on the first stage of the regulator. The high-pressure ports are usually stamped, "HP." The high-pressure port threads are larger than the low-pressure port threads. That has not always been the case. Many years ago regulators had the same threads on both ports and some divers accidentally put a low-pressure hose on a high-pressure port. When the pressure in the hose exceeded 400 psi it would explode! The spg is put on the high-pressure port. The BCD hose, the alternate air hose, the dry suit hose, and the secondary regulator hose are all attached to low-pressure ports.
How often should a regulator be overhauled? It really depends on how it is used. If it is frequently used in salt water the service should be done at least once per year. A less heavily used regulator in fresh water might require servicing after two years. If the period is much longer certain parts of the regulator may permanently seal due to corrosion. Servicing involves the complete disassembly and cleaning of the regulator, lubrication of the O rings, replacement of worn parts, and function testing. An unserviced regulator may begin to destroy itself due to moving parts scoring other parts.
From Sport Diver, A PADI publication, page 6 Mar 2013
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