REGULATORS?
By Bob Rutledge, MD
NAUI Instructor # 5127
How much do you know about the workings of a regulator? Good understandings of regulator function (and malfunction) can a build diver confidence which may help in a stressful situation. This article presents an overview of regulator function to help alleviate stress caused by simple ignorance.
When it comes to regulators, and diving gear in general, the need for both knowledge and hands-on understanding is essential.
Certainly, all divers should learn hands-on gear assembly, use, and care.
Divers should know common vocabulary such as; yoke, filter, first stage, intermediate pressure hose, second stage, purge button, mouthpiece, exhaust valve, etc. and this vocabulary should be used in discussions. Divers should be able to mate regulator to tank, attach accessory hoses, breathe, purge, retrieve lost second stages, remove the regulator from the tank, rinse and store the regulator. Routine maintenance should be habit and sources of qualified service should be known. These are basics covered by instructors in entry-level Scuba courses.
The need for knowledge goes beyond the hands-on understanding level. Left with only "how to use" information, novice divers may have undue anxiety over minor regulator events. "Why does my regulator do this?" is certainly a common novice question. If anxious questions arise during stress periods they may be the final touch to a full-blown panic. It is with this in mind that I believe all divers should have an understanding of regulator function (and malfunction.) I believe that the short time spent in learning is well worth the instilled confidence. Let's begin with basics.
REGULATORS are pressure reducing and controlling devices.
PRESSURE is a measurement unit of FORCE exerted over an AREA.
It is by manipulating the AREAS within a regulator that the FORCES exerted by PRESSURE are balanced and the PRESSURES thereby manipulated and controlled. This is analogous to the LEVERAGE principle of a teeter-totter as shown in the diagram #1.
Diagram #1 BALANCED FORCES
What major factors are working within the regulator? In general terms, there are four: High Pressure, Low Pressure, Ambient Pressure, and Spring Force.
The Diagram # 2 (Regulator Second Stage) can serve as a specific example.
The force of the compressed spring works to press the valve seat against the volcano orifice and impede gas flow from the intermediate hose. In this case, the intermediate pressure represents the higher pressure. Note that this higher intermediate pressure is exerted only over the small area described by the volcano orifice on the valve seat. The force of the intermediate pressure on the valve seat and the adjustable spring force are balanced just to the point of closing off the gas flow through the orifice. Regulator second stages are commonly "unbalanced" and for the forces to be predictable, intermediate pressure must be held constant. It is the job of the regulator first stage (discussed later) to keep intermediate pressure steady. To start gas flow, the valve seat must be retreated from the orifice. The diaphragm's rocker arm can mechanically pry the valve seat shaft so as to compress the spring and retreat the valve seat. The rocker arm's fulcrum is located to give true mechanical leverage to the diaphragm's force. In addition, the large area of the diaphragm gives both the surrounding ambient pressure and the mouthpiece pressure a large "leverage" similar to that depicted in Diagram #1.
Diagram #2 REGULATOR SECOND STAGE
When the diver reduces pressure at the mouthpiece by an inhalation attempt, the ambient pressure against the large diaphragm area is transmitted through the rocker arm to pry open the valve and allow gas flow. When the diver's lungs fill, mouthpiece pressure returns to ambient pressure and the diaphragm returns to neutral position allowing valve closure (with the aid of the second stage seat spring.) Thus a "demand" regulator responds to inhalation attempts by releasing gas to the diver and stops gas flow when the demand is satisfied.
You might well ask why the increasing ambient pressure of descent doesn't just open the regulator to free flow. This does not happen because ambient pressure is exerted not only on the diaphragm but also on the diver's chest wall. To maintain a normal lung volume, the diver inhales sufficient gas to raise lung pressure to ambient pressure which balances the forces across the chest wall. Muscle movement of the diver's diaphragm and chest wall during inhalation transiently increases lung volume, thereby, reducing lung pressure and mouthpiece pressure thus creating a "demand" on the regulator. Ambient pressure itself is exerted outside the chest during the entire process.
Diagram # 3 REGULATOR FREE FLOW
“Free Flow” can occur if the regulator is not in a diver's mouth and the mouthpiece is pointed upward. In this case, a different situation exists. With the diaphragm deeper in the water than the mouthpiece, it "sees" a higher ambient pressure than the mouthpiece "sees." The pressure differential can create enough force on the diaphragm to open the valve and start gas flow. In other words, the pressure differential created by the water column itself creates the "demand" and causes "free flow." (Diagram 3 illustrates this situation.) If the divers swim upside down on scuba, they may notice that it is slightly harder to inhale. In this case, the diaphragm is at a slightly lesser pressure than usual (swimming face down) and more inspiratory effort is needed to start air flow.
Diagram # 4a REGULATOR FIRST STAGE (Piston)
The next question is "What keeps intermediate pressure high enough to exceed ambient pressure as depth increases?" Maintaining intermediate pressure is the job of the regulator first stage. For the second stage to function predictably, the first stage must provide a steady and adequate intermediate pressure in spite of varying conditions. Examine diagrams # 4a & 4b. (Regulator First Stages.)
Diagram #4b REGULATOR FIRST STAGE (Diaphragm)
In the regulator first stage, ambient pressure is applied over a relatively large area (either a piston surface or a diaphragm). The resultant force of ambient pressure is directed to open the valve. Adjustable spring force is applied in concert with ambient pressure force to aid in valve opening. With the valve open gas will flow into the intermittent pressure chamber and hose. Intermediate pressure will build up with the incoming gas. Intermediate pressure is exerted against the chamber side of the piston or diaphragm and the resultant force will close the valve when intermediate pressure reaches a set level. Adjusting the spring force determines the set level for intermediate pressure and this level is held constant.
Real intermediate pressure is a preset value relative to ambient pressure. That is to say, absolute intermediate pressure is a preset value plus ambient pressure. The intermediate pressure that the second stage valve "sees" includes ambient pressure just as the mouthpiece pressure does. Therefore, inhalation effort stays essentially the same as depth increases (disregarding the fact that denser air at greater depths offers more resistance.)
You should now be able to identify the four forces at work in both stages of the regulator. In the case of the regulator first stage, intermediate pressure is the "lower pressure" and tank pressure is the "higher pressure." Tank pressure decreases from very high to near ambient during a dive. Modern regulators are designed to eliminate the influence of this varying tank pressure. In a truly "balanced" regulator first stage (as most are), tank pressure is exerted over no area. In diagrams 4a & 4b, note that higher (tank) pressure is not exerted on the seat of a balanced first stage. This is in contrast to (intermediate) pressure that is exerted on the seat of an unbalanced second stage (Diagram 2.) When pressure is exerted over no area it can generate no force (by definition.) With variable tank pressure having no influence, the balance of forces depends only upon Ambient Pressure and Spring Force that combine to determine Intermediate Pressure that is held constant at a preset value.
The final "basic" of regulator function is the important role played by simple "O" rings. The "O" ring serves as a pressure seal. “O” rings are used at places where regulator components are mated together; particularly at locations where movement between components must be allowed. The diagram #5. ("O" Ring Cross-Sections) illustrates how gas pressure over the curved face of the "O" ring section is transferred through the ring as forces that seal the other ring surfaces against the regulator parts. Within the regulator, the simple “O” ring contains tremendous pressures. The “O” ring that mates the regulator yoke to the tank value is holding back the 3000 psi of a full aluminum cylinder. That is why it is nearly impossible to remove the regulator from the tank until the pressure is relieved.
Diagram #5 "O" RING CROSS SECTIONS
With the preceding concepts to rely on, both usual and unusual regulator events can be appreciated. Regulator "malfunctions" can be divided into two categories: “mal-tunes” and leaks.
“Mal-tunes” occur when springs are improperly adjusted or change over time. If spring forces are relaxed too much, valves will not hold back gas flows; a "free flowing” regulator will exist. If spring forces are exerted in excess, valves will be closed more firmly requiring strain to start gas flows; the regulator will breathe "hard." Corrosion on moving metal parts and stiffening rubber parts can also cause or add to "hard" breathing.
Leaks occur when some fluid (air or water) gets where it shouldn't be. Leaks can be of two types: "In-Leaks" and "Out-Leaks."
Diagram #6 "IN-LEAK" SITES; REGULATOR SECOND STAGE
"In-Leaks" can occur only where internal pressure becomes less than ambient pressure. Therefore, "in-leaks" occur only in regulator second stages and only on the diver's side of the valve. As a diver attempts to inhale, water can be drawn in through a cracked mouthpiece, a split or poorly seated diaphragm or under a curled or debris hindered exhalation valve. Examine these locations in diagram #6. ("In-Leak" Sites, Regulator Second Stage.)
"Out-Leaks" can occur anywhere that internal pressure exceeds ambient pressure. "Out-Leaks" commonly occur from worn "O" rings that no longer make a complete pressure seal on all surfaces. "O" ring leaks can occur at tank attachments, within the regulator itself, and at any hose attachment or swivel. "Out-Leaks" can also occur when valve seats become scored and no longer shut off gas flows completely. A regulator second stage seat leak creates a constant state of slight "free flow." A regulator first stage seat leak, however, has a few moments pause before "free flowing" begins and the "free flow" may be staccato (not continuous) in nature. This occurs because the leaking first stage seat must build up enough intermediate pressure to drive open the second stage seat thus creating the time delay in "free flow." Other "out-leaks" can also occur from cracked housings, loose connections, and hose ruptures but these are uncommon. In modern regulators, even a ruptured high-pressure hose is not the catastrophic event. New high-pressure hoses incorporate a flow-limiting orifice (a tiny hole) at the first stage connection. When a regulator is first pressured this will be noticeable by the much slower stiffening of the high pressure hose as opposed to the intermediate hoses. Modern high pressure hoses are also contained within a perforated sheath. It the internal hose leaks, the sheath will swell and a curtain of tiny bubbles will emerge along its length - a sign to replace the hose immediately.
It should be noted that all of these regulator "malfunctions" continue to provide air to the diver. It may be "wet air" in the case of "in-leaks" or "escaping air" in the case of "out-leaks" or "hard air" in the case of "mal-tunes", but there is air! With a little understanding of underlying regulator mechanics, the diver should be able to stay calm enough to make an expedient exit from the water before air supply or energies are depleted. It is for this reason, this added calm confidence, that this article has been written. For the regulator enthusiast and advanced diver there is much more to know
Revised 2008