Greg Ogle

Southeastern Divers, Inc.

2720 Governors Drive SW, Huntsville Alabama 35805 - Phone: 256-536-8404

"Training the best divers in North Alabama since 1980."

Flat tire? Kick it!

Often we have a customer enter the store with regulator in hand and a disappointed look on their face. The customer will approach the counter and announce, “My regulator is free flowing, and I missed my dive”.

Well . . . what do you mean “it’s free flowing”? Does the air come out of the second stage at full force or is it a slow trickle? There is a difference.

A free flow is a full forceful flow of air that continues on its own. The effect is the same as holding down the purge button at full depression. In fact a good regulator in proper adjustment should do just that. The regulator should continue to flow air at full force after the purge button is depressed fully then released. Many divers don’t know and understand this. We have even had customers bring brand new regulators back and tell us the regulator is “free flowing”. I have even had customers insist that they have been diving for years and have NEVER seen any regulator do this, that NO regulator should do this. If that’s true they have never seen or used a good regulator. I have been selling, rebuilding, adjusting and attending regulator repair technician courses for over 25 years. You WILL lose this argument.

A leak on the other hand is a slow small trickle of air that never stops.

First let’s talk about free flow. As mentioned before, a good regulator should exhibit this behavior. Manufacturers take advantage of something known as Bernoulli’s principle (also called the venturi effect) when designing regulator second stages. Simply stated Bernoulli’s Principle says that when a fluid (in this case the fluid is air) accelerates there is a resulting drop in pressure. This is the same principle that causes lift with the wing of an aircraft. In the case of the regulator second stage when the air in the second stage accelerates due to pressing the purge button the pressure inside the second stage drops. At this point the pressure on the outside of the second stage is greater than the pressure inside the second stage. The pressure on the outside is exerted on the diaphragm thus holding the diaphragm in the depressed position even after you release the purge button and the airflow continues uninterrupted.

However, with that said, there is another category of free flow to consider. On rare occasion a regulator may experience a total or near total failure of the high pressure seat or another component (most likely an o-ring) inside the first stage. When this occurs the intermediate pressure being delivered by the first stage skyrockets well above normal. Normal for most first stages being around 140 psi, give or take 10 psi. Today’s modern regulators are built with a “downstream” valve design. A downstream valve is one in which the seat is downstream of the valve orifice that it seals against. With a downstream configuration the high pressure air will force the seat away from the orifice thereby opening the valve and allowing air to flow. This is a safety feature. An upstream valve would actually be forced closed if the intermediate pressure reached too high a level thereby allowing the pressure to build up to the point where finally the hose from the first stage would fail catastrophically. Not a good thing to happen while underwater. Depending on how high the intermediate pressure goes the resulting free flow could range from a minor leak to a large flow. A regulator second stage will usually begin to flow air when the intermediate pressure approaches 170 – 180 psi or more.

A leak can be anything from a tiny hiss to a loud rush of air. Leaks are usually caused by a failure of the second stage valve seat or the failure of an o-ring or seal in the second stage itself.

So, now that we’ve sorted out the different failure modes of a regulator where does that leave us?

First let’s go back to the first “failure” mentioned, the aerodynamic free flow. We have all been on a dive boat when suddenly someone’s regulator begins to blow air violently. The stricken diver grabs the second stage and begins pounding it on the palm of their hand like they are trying to punish the offending second stage for bad behavior. This act alone can actually cause the very effect they are trying to stop. I have always been amused by this. I have wanted to ask the diver, “When you have a flat tire do you kick it to make it fill back up with air”? You would have about as much success with a flat tire as you will your regulator.

If you take a regulator and give it a sharp rap against the palm of your hand with the mouthpiece pointed to your palm you can cause this to happen. What causes the effect in this case is that when the regulator body comes to a sudden stop against your hand the diaphragm inside continues to move toward your palm due its extreme flexibility. The diaphragm pushes the lever down opening the valve and initiating air flow that then continues due to the aerodynamic effect.

So, how do you stop it you ask? Simply cover the mouthpiece with your hand. This creates backpressure inside the second stage that forces the diaphragm back up into its resting position and allows the lever to rise and close the valve thus stopping the flow of air. Many regulators now come with a switch or knob that you can use to minimize this effect. They are known by many names such as venturi adjustment, vane deflection lever, or others. Whatever they are called they all do the same thing, they impede or slow the flow of air from the second stage thereby allowing the pressure inside the second stage to rise the same way placing your hand over the mouthpiece does. These devices are meant to be set to the “-“ (minus sign), “pre-dive” or other minimal setting when the regulator is not in use but pressurized. This will prevent the “free flow” first mentioned in this article. Once the regulator is in the divers mouth the device should be changed to the “+”, Maximum, or dive setting for use underwater.

In the second case we talked about a failure of a seat or seal. What’s the solution here? There is nothing you can do about this one other than bring it in for service.

What should you do if it happens underwater during a dive? Depending on the severity you may be able to continue to breathe from the regulator. Do you remember that skill from your Open Water course? You might want to practice it from time to time. You could switch to your alternate also. Either way it’s time to end the dive and have your regulator serviced.

Finally what about those slow “leaks”? A minor adjustment might be a temporary fix; however this needs to be done by a service technician trained to work on that specific model and make of regulator. Either way it is still a sign that something is wrong and your regulator needs work. If it happens underwater you should be able to continue to breath on the regulator as you ascend to the surface.

What can a diver do to prevent having to deal with these issues while diving?

My suggestion is own your own regulator. You will come to know and understand how it works and behaves. You will better understand how to use your regulator. You will know when and how it has been maintained and serviced. Regulator service is a very important, and unfortunately, sometimes overlooked part of regulator ownership.

See you next time!

Greg

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