DKW 3 DiveEquip

7/29/2019 DKW 3 DiveEquip

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Section Three: Dive Equipment 3

Section Three

Dive EquipmentScuba diving is an equipment-intensive activity. Therefore, you cannot consider yourunderstanding of diving theory complete without a thorough knowledge of this vital subject.The equipment used by divers varies from convenience items such as underwater lights anddive knives, to essential items such as exposure suits and buoyancy control devices, to highlysophisticated life support systems such as tanks and regulators. Further complicating thepicture is the ever-increasing application of computer technology to the design of moderndiving equipment.

Unfortunately, due to its apparent complexity many divers are reluctant to learn moreabout their equipment because they believe they are not mechanically inclined. This is amisconception. You neednt be a repair technician or a design engineer to understand the

workings of modern scuba equipment. The fundamentals are actually quite simple. Besides,whats important is that you understand the concept of how diving equipment operates, notthe technical details. Thats the purpose of this section to provide you with a conceptualunderstanding of diving equipment. Even if you have difficulty changing a tire, youll find theconcepts discussed in this section to be simple and straightforward.

Objective 3.1

Explain the meaning of each legally required mark that appears on the neck of ascuba tank including: alloy designation, hydrostatic test date, working pressure, andoverpressurization designation.

Resources:

Encyclopedia, Chapter Three, in the side-bar article entitled DecipheringCylinder Hieroglyphics.

Exercises:

1. Which of the following tank markings designates the type of metal used to construct thescuba tank?

a. 3ALb. 7@89

c. 675432

d. 3000

RESET


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3-2 Diving Knowledge Workbook

2. Which of the following tank markings designates the hydrostatic test date?

a. 3AL

b. 7@89

c. 675432

d. 3000

3. The (+) designation that appears on _____________ tanks denotes that the tank may beoverfilled to _____________ beyond its working pressure.

a. steel/15%

b. aluminum/10%

c. steel and aluminum/10%

d. steel/10%

Objective 3.2

Contrast the differences between steel and aluminum scuba tanks in terms of theirrelative ability to resist corrosion and calculate the capacity of tanks with differentpressure and volume.

Resources:

Encyclopedia, Chapter Three, in the sidebar article entitled International CylinderCapacity Conversions Made Easy and under the heading Cylinders Materials

Exercises:

1. A steel tank whose capacity is 2016 litres/71.2 cubic feet at 168 bar/2475 psi and analuminum tank whose capacity is 2265 litres/80 cubic feet at 203 bar/3000 psi are bothfilled to 133 bar/2000 psi. Which tank contains more air?

a. The steel tank

b. The aluminum tank

c. Both would hold equal amounts

d. The answer cannot be determined from the information given.

1. European Metric: An 8 litre tank is filled to 300 bar and a 12 litre tank is filled to175 bar. Which tank will hold the greatest amount of air?

a. The 8 litre tankb. The 12 litre tank

c. Both would hold equal amounts

d. The answer cannot be determined from the information given.


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2. Aluminum tanks were introduced because aluminum is a stronger metal and enableshigher working pressures than in steel tanks.

True False

Objective 3.3

Explain the purpose of a J valve and how it is designed to work.

Resources:

PADI Rescue Diver Manual, Chapter Two, under the heading Tanks andTank Valves

Exercises:

1. The J-valve was designed as a means to:

a. increase the reliability of the internal working mechanism.

b. prevent the tank from rupturing if it is grossly overfilled.c. warn the diver he has run low on air.

d. All of the above are correct.

2. A scuba tank equipped with a J-valve is capable of holding 20-35 bar/300-500 psi moreair than a tank without such a valve.

True False

Objective 3.4

Explain the safety device and design feature that prevents an over-pressurized scubatank from exploding.

Resources:

Encyclopedia, Chapter Three, under the heading Cylinders Features.

Exercises:

1. To prevent a scuba tank from rupturing due to overpressurization, a burst disk is installedin the _____________, and is designed to rupture when the tank pressure rises above

about _____________ of the tanks rated pressure.a. regulator/200%

b. tank neck/225%

c. valve/140%

d. submersible pressure gauge/125%


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2. Why is it important that a burst disk be replaced regularly?

3. What is the primary advantage of the newer type of burst disk assembly that allows air tovent to the sides rather than straight out?

Objective 3.5

Explain the effect of extreme heat upon the structural integrity of a scuba tank, andwhat should be done in the event tanks are exposed to such conditions.

Resources:

Encyclopedia, Chapter Three, under the headings Scuba Cylinder Care andMaintenance and Cylinders - Features

Exercises:

1. Explain why it is important to avoid any process involving heat treatment when having ascuba tank painted or refinished.

2. To ensure the structural integrity of a scuba tank, it should be _____________ anytime it is_____________.

a. destroyed/at an age of twenty years

b. hydrostatically tested/exposed to temperatures above 82C/180F

c. visually inspected/left unused for more than two yearsd. All of the above are correct


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Objective 3.6

Explain how scuba tanks are hydrostatically tested, and to what pressure this test isconducted.

Resources:

Encyclopedia, Chapter Three, under the heading Scuba Cylinder Careand Maintenance.

Note: Tank testing procedures vary from country to country. You are encouragedto learn more about local test procedures from your PADI Dive Center or Instructor.

Exercises:

1. During a hydrostatic test a scuba tank is placed in a water-filled chamber. The tankis then filled with compressed air and the amount of expansion that occurs in the tankis measured by the amount of water that is displaced.

True False2. To what pressure is a scuba tank filled during a hydrostatic test?

a. 340 bar/5000 psi

b. 200 % of its working pressure

c. 5/3s of its working pressure

d. The exact pressure depends upon what happens to the tank once it is pressurized

Objective 3.7List at least three reasons a scuba tank should be visually inspected annually.

Resources:

Encyclopedia, Chapter Three, under the heading Scuba Cylinder Care andMaintenance.

Exercises:

1. Under what circumstances should a scuba tank be visually inspected?

a. If loose material is heard rolling around inside the tank

b. If a red or green accumulation is seen on the filter of the regulator first-stage

c. Once every year even if the tank appears in good condition

d. All of the above are correct


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2. List three reasons why a visual inspection is performed on a scuba tank:

a.

b.

c.

Objective 3.8

Explain the term open-circuit demand regulator and describe what advantages thisdesign has over other types.

Resources:

Encyclopedia, Chapter Three, under the heading Regulators.

Exercises:

1. The term open circuit refers to the fact that:a. electricity is used to test the regulators air-flow rate.

b. the regulator is made from nonmagnetic metal.

c. the exhaled air is released directly into the water.


2. The term demand valve refers to the fact that the regulator will provide air:

a. during both inhalation and exhalation.

b. only upon inhalation.

c. only upon exhalation.d. at a constant flow regardless of the inhalation effort.

3. Identify three primary advantages of the open-circuit, demand valve regulator.

a.

b.

c.


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Objective 3.9

List the major parts and explain the general function of the first and second-stage of ascuba regulator.

Resources:

Encyclopedia, Chapter Three, under the heading Regulators Features PADI Rescue Diver Manual, Chapter Two, under the heading Equipment Function

and Function Related Problems

Exercises:

1. Explain the basic function of the first-stage of a scuba regulator:

2. Explain the basic function of the second-stage of a scuba regulator:

3. What are two advantages of a DIN connector over the standard yoke screw type?

a.

b.

4. A pilot valve refers to a second-stage design that:

a. uses a small valve to assist the opening of the main valve.

b. directs the air flow more directly to the diver.

c. requires the use of an ultra-high pressure tank.d. All of the above are correct.


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Objective 3.10

Define the term fail-safe as it relates to regulator design and how this featureoperates in the event of regulator malfunction.

Resources:

Encyclopedia, Chapter Three, under the heading Regulators Features.

Exercises:

1. Fail safe refers to a regulators tendency to _____________ because of the use of a(n) _____________ valve in the second-stage.

a. breathe easily/open circuit

b. free-flow/downstream

c. breathe easily/closed circuit

d. free-flow/upstream

2. What is the primary advantage of the fail-safe design?

Objective 3.11Define the term environmental seal and what this device is designed to prevent.

Resources:

Encyclopedia, Chapter Three, under the heading Regulators Features.

Exercises:

1. An environmental seal operates by:

a. not allowing water to directly contact the first-stage piston or diaphragm.b. not allowing water to directly contact the second-stage piston or diaphragm.

c. increasing the temperature of the first-stage.

d. causing increased turbulence in the air flow of the first-stage.


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2. What are two advantages of an environmental seal of the first-stage?

a.

b.

Objective 3.12

Define the terms balanced, unbalanced, upstream and downstream as theyrelate to regulator design.

Resources:

Encyclopedia, Chapter Three, under the heading Regulators Features and in theside-bar article entitled The Differences Between Balanced and Unbalanced Valves

Exercises:

1. A valve that tends to open in the direction of flow is referred to as _____________ whilea valve that tends to close in the direction of flow is referred to as _____________ .

a. open circuit/closed circuit

b. closed circuit/open circuit

c. upstream/downstream

d. downstream/upstream

2. The primary advantage of a balanced first-stage over an unbalanced one is that:

a. they breathe easier at greater depths, even at low tank pressures.

b. they provide greater air flow.

c. they are better able to supply a second diver breathing from an octopus.



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Objective 3.13

Explain the proper procedures for the use of dive computers among buddy teams.

Resources:

PADI Divemaster Manual, Section Five, under the heading Special Rules,

Recommendations and Situations Using the RDP and Computers PADI Open Water Diver Manual, Chapter Five, under the heading Using a

Dive Computer

Exercises:

1. Two divers may use a single dive computer provided they are careful to remain togetherand dive the exact same profile.

True False

2. A buddy team exits the water. Both divers are using dive computers. After a short surfaceinterval, they plan another dive to 18 metres/60 feet. One device allows 38 minutesof bottom time at 18 metres/60 feet, the other allows only 32 minutes. Based on thisinformation how should they plan their dive?

a. Plan a maximum bottom time of 38 minutes because computers are intentionallydesigned to be more conservative than dive tables.

b. Plan a maximum bottom time of 32 minutes because computers are intentionallydesigned to be more conservative than dive tables.

c. Plan a maximum bottom time of 38 minutes but be sure to make a safety stopbefore surfacing.

d. Plan a bottom time of somewhat less than 32 minutes and make a safety stopbefore surfacing.


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Section Three: Dive Equipment 3-

Objective 3.14

State the type of depth gauge which automatically compensates for high altitude diving.

Resources:

Encyclopedia, Chapter Three, under the sub-heading Instrument Specifics.

Adventures in Diving, Section One, Altitude Diving

Exercises:

1. A capillary depth gauge works by using:

a. a simple system of pressure sensitive gears.

b. a mechanical pressure transducer.

c. Boyles Law.

d. Archimedes Principle.

2. While on a dive in a mountain lake at an altitude of 3,000 metres/10,000 feet, a diverchecks his depth. He is using a capillary depth gauge which indicates a depth of 14metres/45 feet. If he actually measured the linear distance to the surface from where heis, he would find that:

a. he is exactly 14 metres/45 feet beneath the surface.

b. he is actually more than 14 metres/45 feet below the surface.

c. he is actually less than 14 metres/45 feet below the surface.

d. The answer cannot be determined from the data provided.


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Objective 3.15

List at least three reasons related to equipment why divers should always avoidmaximum decompression limits.

Resources:

Encyclopedia, Chapter Three, under the sub-heading Instrument Specifics. PADI Deep Diver Manual

Exercises:

1. In terms of equipment considerations, avoiding the maximum limits of the dive tables iswise because:

a. dive tables are imprecise.

b. its hard to read dive tables while underwater.

c. depth gauges can malfunction and/or be read inaccurately.d. you can get nitrogen narcosis more easily.

2. What special considerations are important in terms of equipment when planning adeep dive?

a. The diver will use air more quickly than at a shallower depth.

b. Breathing will become more difficult than at a shallower depth.

c. The diver may have difficulty controlling his descent/ascent.



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Section Three: Answer Key 3-

Correct:ConfidentGuess

Incorrect:Simple MistakeLack of Knowledge





Section Three

Answer KeyObjective 3.1

Explain the meaning of each legally required mark that appears on the neck of ascuba tank including: alloy designation, hydrostatic test date, working pressure, andoverpressurization designation.

1. (a)Which of the following tank markings designates the typeof metal used to construct the scuba tank? 3AL. The designation3AL indicates that the tank is made from an aluminumalloy approved by the U.S. Department of Transportation.

(Aluminum tanks produced prior to July 1, 1982 will have othedesignations). 3AA indicates that the tank is made from anapproved alloy of chromemolydbenum steel. 3A would indicatean older carbon steel alloy that is more prone to corrosion.

2. (b) Which of the following tank markings designates thehydrostatic test date?7@89. This designation indicates thatthe tank was hydrostatically tested in July (the 7th month) of1989. The @ is a mark registered with the U.S. Departmentof Transportation used to identify the test facility. Within theU.S. this test is legally required at least every five years. Therequirement varies outside of the U.S.

3. (d) The (+) designation that appears on steeltanks denotes thathe tank may be overfilled to10%beyond its working pressureThis mark is valid only during the period of the first hydrostatictest, unless a (+) appears after subsequent hydro tests. Also,some countries may not allow 10% overfilling.

Note: tank markings vary from country to country. You areencouraged to learn more about local tank markings from yourPADI Dive Center or Instructor.


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Objective 3.2

Contrast the differences between steel and aluminum scuba tanks in terms of maximumpressure, thickness and capacity.

1. Metric (a)A steel tank whose capacity is 2016 litres at 168 bar and

an aluminum tank whose capacity is 2265 litres at 203 barare both filled to 133 bar. Which tank contains more air?Thesteel tank.To answer this question, you need to compare howmuch capacity each bar accounts for. In steel tanks each baraccounts for 12 litres (2016 litres divided by 168 bar = 12 litresper bar). In an aluminum tank each bar accounts for 11.15litres (2265 litres divided by 203 bar = 11.15 litres per bar).

These constants can now be used to quickly determine howmuch capacity remains in a tank of a certain pressure. In thequestion, a steel 2016 litre tank filled to 133 bar contains1596 litres (12 litres per bar x 133 bar = 1596 litres).

An aluminum 2265 litre tank contains only 1482.95 litres(11.16 litres per bar x 133 bar = 1482.95 litres).

Imperial (a) A steel tank whose capacity is 71.2 cubic feet at 2475 psi

and an aluminum tank whose capacity is 80 cubic feet at3000 psi are both filled to 2000 psi. Which tank containsmore air?The steel tank.To answer this question, you needto compare how much capacity each psi accounts for. In asteel tank each psi accounts for .0287 cubic feet (71.2 cubicfeet divided by 2475 psi = .0287 cubic feet per psi). In analuminum tank each psi accounts for .0266 cubic feet

(80 cubic feet divided by 3000 psi = .0266 cubic feet per psi).These constants can now be used to quickly determine howmuch capacity remains in a tank of a certain pressure. In thequestion, a steel 71.2 cubic foot tank filled to 2000 psi contains57.4 cubic feet (.0287 cubic feet per psi x 2000 = 57.4 cubicfeet). An aluminum 80 cubic foot tank contains only 53.2 cubicfeet (.0266 cubic feet per psi x 2000 psi = 53.2 cubic feet).

European Metric (a)An 8 litre tank is filled to 300 bar and a 12 litre tank is filled to

175 bar. Which tank will hold the greatest amount of air?The

8 litre tank. The size of the tank is measured from the internalvolume (just like the gas tank in a car), and an 8 litre tank contains8 litres of compressed air. To determine the tanks capacity, wesimply multiply the volume with the pressure. The answer tells ushow many litres of air at 1 atm the tank contains. In this questionthe 8 litre tank contains 2400 litres of air (8 x 300 = 2400 litres).The 12 litre tank contains 2100 litres (12 x 175 = 2100 litres).

Correct:Confident

GuessIncorrect:

Simple MistakeLack of Knowledge






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2. Aluminum tanks were introduced because aluminum is astronger metal and enables higher working pressures than insteel tanks. False. The reason aluminum was introduced wasbecause of its resistance to corrosion, not its strength.

Objective 3.3

Explain the purpose of a J-valve and how it is designed to work.

1. (c) The J-valve was designed as a means to: warn thediver he has run low on air. The J-valve, which predatesthe submersible pressure gauge, was an early mechanicalwarning device that signaled a tank was running low on air.At approximately 20 to 35 bar/300 to 500 psi (dependingon the spring tension), the reduced pressure enables a springmechanism to begin shutting off the air flow, thereby warning the

diver of low air. By activating the valve usually by pulling alever to the down position the mechanism is released andnormal air flow restored. With the advent of the submersiblepressure gauge, J-valves began to disappear. In fact, when usinga J-valve, many divers often disable it by keeping in the downposition. Incidentally, be careful when filling tanks equipped with

J-valves. They cannot be filled if the valve is in an up position.

2. A scuba tank equipped with a J-valve is capable of holding20-35 bar/300-500 psi more air than a tank without such avalve. False. A tank is a tank; it can only hold a certain capacity

regardless of the valve it uses. As was explained in the previousanswer, the J-valve merely warns the diver that the tank is low onair. A K-valve, which is merely an on/off valve, does not do this

Objective 3.4

Explain the safety device and design feature that prevents an over-pressurized scuba tank from exploding.

1. (c) To prevent a scuba tank from rupturing due to over-pressurization, a burst disk is installed in thevalve,and is

designed to rupture when the tank pressure rises above about140%of the tanks rated pressure. The burst disc is installed inthe valve in such a way that if it were to rupture while someonewas wearing the tank the force would be directed away from thewearers head.







Correct:Confident

GuessIncorrect:



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Replacement of the disk should always be performed by atrained repairman to avoid inserting the wrong disk. A diskrated for an aluminum tank is not designed to blow untilreaching a pressure of about 285 bar/4200 psi. This is greaterthan the hydrostatic test pressure of most steel tanks! The resultsof such a mix-up could be disastrous.

2. Why is it important that a burst disk be replaced regularly?

With the continual filling and emptying of a tank, the burst diskis constantly stressed. In fact, when they are removed duringregular maintenance of the valve, burst disks are always bent ordimpled. As this causes the metal to weaken, the disk couldblow at a pressure far lower than its rated pressure. Therefore,the disk should be replaced on at least an annual basis.

3. What is the primary advantage of the newer type of burstdisk assembly that allows air to vent to the sides rather thanstraight out?Older burst disk plugs allow the air escaping fromthe tank to vent directly out (the force is directed perpendicular

to the tank valve). When the disk ruptures, this design cancause the tank to spin sometimes out of control. The newerplugs are vented to redirect the air at a 90-degree angle,preventing the potential for spinning. Be sure your tank valvecontains the newer style plug. If not, replace it.

Objective 3.5

Explain the effect of extreme heat upon the structural integrity of a scuba tank, andwhat should be done in the event tanks are exposed to such conditions.

1. Explain why it is important to avoid any process involving heattreatment when having a scuba tank painted or refinished.The molecular structure of metal can easily be altered by theapplication of heat. One of the most common alterations is tomake the metal more brittle and therefore less able to withstandconstant expansion and contraction. Some exterior finishingprocesses not intended for scuba tanks use heat as partof the procedure. When exposed to heat in excess of about82C/180F, scuba tanks can lose their flexibility. Therefore,rather than expanding while it is filled, it can rupture. Severalserious injuries, and at least one death, have resulted from tanksexploding while being filled after heat treatment. Never use anyform of heat treatment to have your tanks refinished!






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2. (b) To ensure the structural integrity of a scuba tank, it shouldbehydrostatically testedanytime it is exposed totemperatures above 82C/180F. The heat issue wasexplained in the previous answer. The age of the tank is not in andof itself a factor. Many tanks well over twenty years of age are stilin use today. Older tanks are fine as long as they are structurallysound. However, if a tank is left unused for more than two years,it shouldnt just be visually inspected; it should be hydrostaticallytested as well. That is the only way to confirm its structural integrity

Objective 3.6

Explain how scuba tanks are hydrostatically tested, and to what pressure this testis conducted.

1. During a hydrostatic test a scuba tank is placed in a water-filledchamber. The tank is then filled with compressed air and theamount of expansion that occurs in the tank is measured by theamount of water that is displaced. False. During a hydrostatic

test a scuba tank is placed in a water-filled chamber. The tankis then filled with water, which is safer, easier and less expensivto pressurize. As the water pressure within the tank is increasedthe amount of expansion that occurs in the tank is measured bythe amount of water that is displaced in the exterior reservoir.When the internal pressure is released, the degree to which thetank recon-forms to its original size is measured. In essence,what is measured is the tanks flexibility. Tanks that do notreconform to a point very close to their original size fail the testand are condemned.

Note: tank testing procedures vary from country to country.You are encouraged to learn more about local test proceduresfrom your PADI Dive Center or Instructor.

2. (c)To what pressure is a scuba tank filled during a hydrostatictest?5/3s its working pressure. To measure the flexibilityof a tank during hydro, U.S. Department of Transportationregulations mandate that it be filled to 5/3s its working pressurThis means a 153 bar/2250 psi steel tank is tested to a pressuof 255 bar/3750 psi. A 203 bar/3000 psi aluminum tank istested to 338 bar/5000 psi.

Note: hydrostatic testing procedures vary from country tocountry. You are encouraged to learn more about local testprocedures from your PADI Dive Center or Instructor.






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Objective 3.7

List at least three reasons a scuba tank should be visually inspected annually.

1. (d) Under what circumstances should a scuba tank be visuallyinspected?All of the responses are correct. Loosematerial could cause the valve to clog or indicate some other

more serious problem. Red or green accumulation on thefirst-stage filter indicates that there is a significant amount ofcorrosion or foreign material within the tank. And finally, evenif nothing appears to be wrong with the tank, it should alwaysbe visually inspected at least annually. Tanks used extensively inseawater should, in fact, be inspected even more often.

2. List three reasons why a visual inspection is performed on ascuba tank:a. To detect exterior damage such as severe scratches or dents.

Severe external damage can weaken the tank just as severeinternal corrosion.

b. To detect severe interior corrosion, particularly in steel tanks.Excessive internal corrosion could clog the tank valve. Insteel tanks a form of corrosion called pitting can actuallyweaken the tank structurally long before a hydro is required.

c. To prevent galvanic action between the dissimilar metalsof the tank and valve threads. Particularly in sea-water theelectrolysis resulting from contact of dissimilar metals canactually cause the valve and tank thread to seize. In thiscase the valve cannot be removed without destroying thethreads. A visual inspection is a small price to pay to avoidthis problem.

Objective 3.8

Explain the term open-circuit demand regulator and describe what advantages thisdesign has over other types.

1. (c) The term open circuit refers to the fact that: theexhaledair is released directly into the water.In this context,open-circuit has nothing to do with electrical or magneticconductivity. It simply means that the path of the air from thetank terminates when it is exhaled into the water. This is in

contrast to a closed-circuit system where the exhaled air iscaptured, filtered, reoxygenated and returned to the diver tobe rebreathed.




Incorrect:



Incorrect:Simple Mistake

Lack of Knowledge


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2. (b) The term demand valve refers to the fact that the regulatorwill provide air: only upon inhalation. This is easilyremembered by thinking of the regulator providing air only onthe divers demand. The demand is the divers inhalation. Onexhalation, the valves close and air flow is terminated until thenext demand (breath).

3. Explain the three primary advantages of the open-circuit,demand valve regulator:a. It uses less air than a free-flow system. Free flow systems

require a surface air supply, like those used in commercialdiving. Obviously a scuba tank would be severely limited inproviding such great amounts of air.

b. It avoids carbon dioxide buildup by reducing dead airspaces. Surface-supplied helmets or hats, as theyare referred to in commercial diving allow exhaledair to build up inside them. This means carbon dioxide isconstantly accumulating. To avoid the problem of excessive

carbon dioxide buildup the hat must be periodically purgedor flushed. As there is so little dead air in the second--stageof a scuba regulator, carbon dioxide build-up is insignifican(Although significant buildup of carbon dioxide can occurwithin the diver himself.)

c. It is simpler and less expensive than closed-circuit systems.Closed-circuit systems, although far safer today than in thepast, do create special problems due to their complexity. Inaddition, they are currently cost prohibitive for recreationaldiving.

Objective 3.9List the major parts and explain the general function of the first and second-stage of ascuba regulator.

1. Explain the basic function of the first-stage of a scuba regulatorAlthough there are a wide array of styles and models of scubaregulators, they all function in fundamentally the same way they are pressure-reduction valves. As such, the first-stagetakes the tremendously high pressure air in the tank and reduceit to an intermediate pressure. This intermediate pressure variesaccording to the design and manufacturer of the regulator,but its normally between about 6 bar/85 psi to 10 bar/140psi plus the ambient water pressure. (If the regulator could notcompensate for the ambient water pressure, then it couldntdeliver air once the ambient water pressure exceeded theintermediate pressure rating).








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2. Explain the basic function of the second-stage of a scubaregulator. The second-stage continues the process discussed inthe above item. It takes the intermediate pressure from the first-stage and breaks it down to a pressure equal to the surroundingwater pressure. The ambient pressure is sensed by a flexiblesecond-stage diaphragm.

3. What are the two advantages of a DIN connector over the

standard yoke screw valve? Long popular in Europe, DIN(Deutsche Industrie-Norm) connectors are becoming morecommon in the U.S. They provide two primary advantages overthe yoke screw design:a. A better seal between the tank and regulator valves because

the O-ring is actually trapped between the two valves. (Thetank valve is female and the regulator connector is male.)

b. Because the tank valve and regulator are secured bythreads, the connection is much stronger than the yoke screwassembly. In addition, the O-ring is enclosed deep withinthe tank valve and is more stable. This system, because of its

high security, enables the use of much higher air pressures.

4. (a) A pilot valve refers to a second-stage design that: uses asmall valve to assist the opening of the main valve.A pilot valve uses a smaller valve as a helping hand to openthe main second-stage valve. Because less effort is required toactivate the smaller assisting valve, pilot valve regulators tendto breathe more responsively. However, because they are moresophisticated, they require more maintenance.

Objective 3.10

Define the term fail-safe as it relates to regulator design and how this featureoperates in the event of regulator malfunction.

1. (b) Fail safe refers to a regulators tendency tofree-flowbecause of the use of a(n) downstreamvalve in the second-stage. A downstream valve means that it will tend to open withthe flow of air. Therefore, if a problem occurs in the first-stage,the air flow will open the valve allowing air to escape to thesecond-stage. Then, the downstream design of the second-stagevalve will also open, causing the regulator to free-flow. This is avital safety feature.










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2. What is the primary advantage o the ail-sae design?Theprimary advantage o the ail-sae design o regulators is thatin the event o a malunction, air is still delivered to the diver.Although the air fow is continuous, its a situation the divercan deal with while ascending to the surace. Never continuea dive with a ree-fowing regulator even i the air fow ismanageable.

Objective 3.11

Dene the term environmental seal and what this device is designed to prevent.

1. (a) An environmental seal operates by: not allowingwater to directly contact the frst-stage piston ordiaphragm. When high pressure air depressurizes it draws atremendous amount o heat rom the surrounding environment.Imagine i this reduction in temperature were to occur in waterthat is already near reezing. Any water within the rst-stagewould then reeze and prevent the open valves rom closing.

This is reerred to as a regulator reeze-up. This problem canbe avoided by preventing water rom getting into the rst-stageHowever, whatever substance is used to ll the rst-stage musthave a reezing point well below the reezing point o water.Substances such as alcohol or silicone grease are normally useor this purpose. This is an important consideration or thosewho dive in extremely cold water.

2. What are the two advantages o an environmental seal o therst-stage?The primary advantage o an environmental sealis described in the previous answer it prevents reeze-up.

However, a second advantage is that in preventing water romentering the rst-stage, dirt and oreign matter are also keptrom entering the rst-stage.

Objective 3.12

Dene the terms balanced, unbalanced, upstream and downstream as theyrelate to regulator design.

1. (d) A valve that tends to open in the direction o fow is reerredto as downstream,while a valve that tends to close in the

direction o fow is reerred to as upstream.This concept waspartially explained in item 1 o objective 3.10. An easy way tounderstand it is to think o how you enter a room. I you can pusha door open it opens with you then the door is said to bedownstream. I, on the other hand, you must pull the door toward

you it opens against you the door is said to be upstream.

Correct:

ConfdentGuess

Incorrect:

Simple MistakeLack o Knowledge

Correct:

ConfdentGuess

Incorrect:


Correct:

Confdent

GuessIncorrect:


Correct:

ConfdentGuess

Incorrect:



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2. (d) The primary advantage of a balanced first-stage over anunbalanced one is that:All the responses are correct.In a balanced regulator design, the operation of the valvesare unaffected by the pressure in the tank. Rather than the airforcing the valves of the first-stage open, the force is directedaround them. As a result, larger orifices can be used providingmore air flow to the diver. This, in turn, makes the regulatorbreathe easier than a similar though unbalanced design. Thegreater air flow also makes it easier to supply a second diverwho might be breathing from an alternate air source.

Objective 3.13

Explain the proper procedures for the use of dive computers among buddy teams.

1. Two divers may use a single dive computer provided they arecareful to remain together and dive the exact same profile.False. A buddy team should never share a single computerbecause no matter how hard they try, both buddies can never

dive the exact same profile. Therefore, for optimal safety, eachdiver must have his own computer.

2. (d) A buddy team exits the water. Both divers are using divecomputers. After a short surface interval, they plan anotherdive to 18 metres/60 feet. One device allows 38 minutes ofbottom time at 18 metres/60 feet, the other allows only 32minutes. Based on this information how should they plan theirdive?Plan a bottom time of somewhat less than 32minutes and make a safety stop before surfacing.In the scenario described, the divers should not only use the

more conservative computer, but cut a few minutes of theremaining time as well. When planning bottom time, always beconservative. Using the more conservative computer to controlthe dive is the wisest practice. In addition, because little isknown about the decompression phenomenon, and individualsvary considerably in their susceptibility to decompressionsickness, no dive table or computer should ever be dived toits limit. For this same reason, making a safety stop at theconclusion of every dive is also advised.








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3. (b) Which portion of the ear is most affected by changesin pressure?middle ear. The outer ear structures (canal,lobes) are open to the water, and are unaffected by changesin ambient pressure. Like any air-filled structure of the body,the middle ear is affected by changes in ambient pressure.Although what occurs in the middle ear can, in turn, affectthe inner ear, the inner ear itself is not directly affected by thechange in ambient pressure because it is fluid-filled.

Objective 3.14

State the type of depth gauge which automatically compensates for highaltitude diving.

1. (c) A capillary depth gauge works by using: Boyles Law. Acapillary depth gauge is merely an empty plastic tube open at oneend to allow water to enter. In accordance with Boyles Law, theinternal air space will fill with water in a predictable manner half the original volume at 10 metres/33 feet, one third at 20/66

one fourth at 30/99, etc. By marking off where the water columnwill be at various depths, a crude but highly accurate gaugecan be constructed with no moving parts. In practice, however,capillary gauges are plagued by problems such as difficulty inseeing the rising water column, increasingly small increments ofdepth beyond 66 feet, and air bubbles getting into the tube. Forthese reasons capillary gauges are rarely used as the sole meansof determining a divers depth. They are most commonly used asbackup devices in shallow water.

2. Metric

(c) While on a dive in a mountain lake at an altitude of 3,000metres, a diver checks his depth. He is using a capillary depthgauge which indicates a depth of 14 metres. If he actuallymeasured the linear distance to the surface from where he is, hewould find that: he is actually less than 14 metres belowthe surface. This sounds strange until we remember how acapillary depth gauge works. A closed air space will fill withwater in accordance to the relative atmospheres it is exposed to.In essence, it will show a relationship of atmospheres rather thanindicate an actual ambient pressure.

For example, from sea level an open container (such as a

capillary gauge) is taken to two atmospheres. It will be halffull. As we started at one atmosphere at the surface, twice thatpressure would be two atmospheres. This we know occurs at10 metres. But remember, the capillary gauge is actually tellingus that the depth is twice the surface pressure not that thepressure is 2 ata. Lets compare this to what would happen at




Incorrect:


Correct:

ConfidentGuess


Imperial Answer


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altitude. We will start from an altitude equal to a surface pressureof 0.7 atm (this occurs at about 3,000 metres). In this instance1 atmosphere is no longer 1 ata, but rather 0.7 atm. Thereforetwo atmospheres will not be 2 ata, but rather 1.4 atm. Note thatthe second atmosphere occurred much more quickly becausethe first atmosphere was less than that at sea level. In fact, if westart from an atmospheric pressure of 0.7 atm, we can easilydetermine that the pressure of 1.4 atm occurs at a depth of 7meters in fresh water. (0.7 atm divided by 0.100 atm/m = 7m.)Although the diver is at two atmospheres, he is only 7 metresbeneath the surface. Still the capillary gauge, which reads theatmospheric relationship, will indicate 10 metres! Now you canbegin to see why altitude diving requires special procedures, andwhy special training should be sought.

Imperial(c) While on a dive in a mountain lake at an altitude of10,000 feet, a diver checks his depth. He is using a capillarydepth gauge which indicates a depth of 45 feet. If he actuallymeasured the linear distance to the surface from where he is, hewould find that: he is actually less than 45 feet belowthe surface. This sounds strange until we remember how acapillary depth gauge works. A closed air space will fill withwater in accordance to the relative atmospheres it is exposedto. In essence, it will show a relationship of atmospheres ratherthan indicate an actual ambient pressure. For example, fromsea level (1 atmosphere = 15 psi) an open container (suchas a capillary gauge) is taken to two atmospheres. It will behalf full. As we started at 15 psi at the surface, twice thatpressure would be 30 psi. This we know occurs at 33 feet. But

remember, the capillary gauge is actually telling us that thedepth is twice the surface pressure not that the pressure is30 psi. Lets compare this to what would happen at altitude.We will start from an altitude equal to a surface pressure of10 psi (this occurs at about 10,000 feet). In this instance oneatmosphere is no longer 15 psi, but rather 10 psi. Thereforetwo atmospheres will not be 30 psi, but rather 20 psi. Note thatthe second atmosphere occurred much more quickly becausethe first atmosphere was less than that at sea level. In fact, ifwe start from an atmospheric pressure of 10 psi, we can easilydetermine that the pressure of 20 psi occurs at a depth of just

over 23 feet in fresh water. (10 psi divided by .432 psi/ft =23.14 ft). Although the diver is at two atmospheres, he is only23 feet beneath the surface. Still the capillary gauge, whichreads the atmospheric relationship, will indicate 33 feet! Now

you can begin to see why altitude diving requires specialprocedures, and why special training should be sought.



Metric Answer


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Correct:Confident

GuessIncorrect:




Objective 3.15

List at least three reasons related to equipment why divers should always avoidmaximum decompression limits.

1. (c) In terms of equipment considerations, avoiding the maximumlimits of the dive tables is wise because: depth gauges can

malfunction and/or read inaccurately. Analog depthgauges tend to have a wide range of accuracy, particularlywhen you consider that few divers ever have them regularlyrecalibrated. Therefore, if planning a dive to the NDL for aspecific depth, an inaccurate depth gauge one that readstoo shallow could place you in a decompression situationwithout you even being aware of it! So, aside from thephysiological consequences of diving to table limits (an unwisepractice to begin with), the limitations of your equipment alsoshow that it could be doubly unwise.

2. (d) What special considerations are important in terms

of equipment when planning a deep dive?All of theresponses are correct. Because of the increased pressureat depth, the diver must breathe more air from his tank. Thisincreases his rate of air consumption. Secondly, because the aiis much denser at depth, it requires more effort to move it in andout of his lungs. It therefore becomes more difficult to breathe.Lastly, when deep diving, site orientation and controlling therate of descent/ascent becomes difficult. This is why some formof descent line is always advised when deep diving.


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Section AnalysisFrom the answer key, identify any items marked "correct-guess" or "incorrect-lack ofknowledge." These items represent important points of information or concepts you still might

not fully understand. Check below any objectives that contained items with a "correct-guess"or "incorrect-lack of knowledge" response. Completing this section is an important step indetermining your understanding of dive equipment as it relates to recreational diving.

Confident Guess Total

Correct Responses

Simple Mistake Lack of Knowledge Total

Incorrect Responses

Objectives To Be Reviewed:

3.1 3.2 3.3 3.4 3.5

3.6 3.7 3.8 3.9 3.10

3.11 3.12 3.13 3.14 3.15

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