NAUI Equipment Use & Maintenance 4 — Questions and Answers
Question 1: When attaching a first-stage regulator to a DIN valve cylinder, which step is critical to prevent cross-threading?
- Apply silicone grease liberally to all threads before attachment
- Hand-tighten the DIN fitting slowly while ensuring it threads straight (Correct answer)
- Use a wrench to snug the connection before hand-tightening
- Insert the o-ring into the DIN port before threading
Correct answer: Hand-tighten the DIN fitting slowly while ensuring it threads straight
DIN fittings must be started by hand and threaded straight to avoid cross-threading, which can damage both the regulator inlet and the valve.
Question 2: Why should scuba cylinders never be stored fully empty?
- Empty cylinders are more susceptible to implosion under pressure changes
- Moisture and contaminants can enter and cause internal corrosion (Correct answer)
- Storage regulations require a minimum residual pressure of 500 psi
- Valve o-rings dry out faster without positive cylinder pressure
Correct answer: Moisture and contaminants can enter and cause internal corrosion
A small residual positive pressure (typically 200–500 psi) keeps moisture-laden outside air from entering and corroding the interior walls.
Question 3: A diver discovers a small crack in the plastic housing of their dive light before a night dive. What should they do?
- Use the light for the dive since water pressure will seal the crack
- Apply waterproof epoxy and test the light before the dive
- Remove the light from service until it is properly repaired or replaced (Correct answer)
- Wrap the crack with electrical tape as a temporary fix
Correct answer: Remove the light from service until it is properly repaired or replaced
A cracked housing can flood or implode under pressure, causing total light failure or injury; the equipment should not be used until properly repaired.
Question 4: Which type of valve is found on most modern recreational scuba cylinders in the US and allows easy tank-on/tank-off operation?
- J-valve with reserve mechanism
- K-valve (on/off valve) (Correct answer)
- DIN-only valve
- Pillar valve with integrated SPG
Correct answer: K-valve (on/off valve)
The K-valve is a simple on/off valve standard on most US recreational cylinders, replacing the older J-valve with its reserve mechanism.
Question 5: What is the function of the intermediate pressure port on a first-stage regulator?
- It delivers high-pressure gas directly to the SPG
- It supplies reduced pressure gas to the second stage and BCD inflator (Correct answer)
- It vents excess pressure to prevent over-pressurization
- It connects to the drysuit inflation hose only
Correct answer: It supplies reduced pressure gas to the second stage and BCD inflator
The intermediate (low-pressure) port delivers gas reduced to intermediate pressure (typically 120–150 psi over ambient) to second stages and BCD inflators.
Question 6: After rinsing a BCD, how should it be stored to maintain the bladder integrity?
- Fully deflated and folded flat to save space
- With a small amount of air inside and hung upright (Correct answer)
- Submerged in fresh water between dive trips
- Inflated to maximum capacity to stretch the bladder
Correct answer: With a small amount of air inside and hung upright
Storing a BCD with a small amount of air prevents the internal bladder walls from sticking together, which can compromise the bladder over time.
Question 7: A diver notices the o-ring on their cylinder valve is cracked and dry. What is the correct action?
- Apply silicone grease to the cracked o-ring and proceed with the dive
- Replace the o-ring with one of the correct size and material before diving (Correct answer)
- File the crack smooth with fine sandpaper and grease the o-ring
- Use a backup yoke connector to bypass the damaged o-ring
Correct answer: Replace the o-ring with one of the correct size and material before diving
A cracked o-ring will not seal reliably under pressure and must be replaced with a proper replacement before the cylinder is used.
NAUI Equipment Use & Maintenance 4
When attaching a first-stage regulator to a DIN valve cylinder, which step is critical to prevent cross-threading?