Scuba Cylinder Quiz - The Answer Key!

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Image: Pixabay

By Fred Stratton
Instructor & Repair Technician
fred@bubblesornot.com

Special Edition - Cylinder Summary and Answer Key

All right, BoN Crew, how did you do on the cylinder markings quiz?  I'm sure you passed with flying colors! 

Cylinders 101 & 202 - Summary


Now that we've covered cylinder markings you can stay away from sketchy cylinders you may find at yard sales or online. Invest in quality equipment that - with TLC and regular maintenance - will give you decades of reliable service. You might even be more vigilant when renting cylinders during dive trips. If it looks, smells or feels wrong (no VIP sticker, out of date hydro, diesel odor present when you crack the valve, etc.), ask for different cylinders. If the staff look at you sideways, find a more reputable dive shop.


Avoid buying used cylinders made from 6351 alloy. If you have 6351s and just can't part with them, remember to include the price of eddy current tests ( a $15 to $25 test) in the overall cost of keeping these cylinders serviceable. Doing the math quickly reveals that retiring 6351s is financially prudent. This DAN Alert Diver article on 6351-T6 alloy scuba cylinders authored by Mark Gresham of PSI-PCI will help you make an informed decision. 

This Tech Bulletin provides specific dates when Luxfer switched from 6351 to 6061 alloy for each cylinder size (e.g. S72 and S100 in August 1987, M9 in January 1988).

Cylinder Markings Quiz Answer Key

Time to test your knowledge. 

Cylinder One

Q: What company manufactured it? 
A: Luxfer Cylinders (middle right)

Q: When was this cylinder manufactured? 
A: In May 1980 (bottom stamp 5 80) 

Q: Is it steel or aluminum? 
A: Aluminum: Note the E6498 original DOT stamp at top center.  A hydrostatic retesting facility correctly stamped 3AL above E6498 after a successful subsequent hydro.

Q: Is it made of 6351-T6 alloy or 6061-T6 alloy?
A: Luxfer made aluminum cylinders using 6351 alloy from November 1971 through May 1988, so this is a 6351 cylinder.

Q: What is its service pressure?    A: 3000 psi (stamp in upper right)

Q: What is R69125? (middle left)   A: This is the cylinder's serial number. 


Cylinder Two


Q: What company manufactured it?
A: Luxfer

Q: When was this cylinder manufactured?
A: October 1984 (bottom right)

Q: Is it steel or aluminum?
A: 3AL indicates aluminum
Q: Is it made of 6351-T6 alloy or 6061-T6 alloy?
A: Luxfer made aluminum cylinders using 6351 alloy from November 1971 through May 1988, so this is a 6351 cylinder. 

Q: What is its service pressure?  A: 2015 psi. Even though this is an aluminum cylinder, Luxfer rates it to 2015 psi (not 3000) because it is utilized for 100% oxygen. 

Q: What testing or inspection is required of this cylinder in addition to annual visual inspections and 5-year hydros?
A: It must pass an Eddy Current Test and get VE stamped to the right of the hydro stamp in order to remain in service. 



Cylinder Three

Explain all the markings on this cylinder.
TC-3AL M207, DOT-3AL 3000, LS9479, LUXFER, 03-04, 2-10, S040

TC-3AL M207 = Transport Canada specification for aluminum with a Metric system service pressure (maximum) of 207 bar

DOT-3AL 3000 = Dept. of Transportation specification for aluminum with service pressure (maximum) of 3000 psi

LS9479 = cylinder serial number

Luxfer = manufacturer

03-04 = original hydrostratic test performed in March 2004

2-10 = hydrostatically retested in February 2010

S040 = cylinder used for Scuba with capacity of 40 cubic feet (when filled to its rated service pressure of 3000 psi)


Cylinder Four


Explain all the markings on this cylinder.
TC-3AL M207 BAR, DOT-3AL 3000, CATALINA, BJ06396, M4002, 09-97, S063
TC-3AL M207 = Transport Canada specification for aluminum with a Metric system service pressure (maximum) of 207 bar

DOT-3AL 3000 = Dept. of Transportation specification for aluminum with service pressure (maximum) of 3000 psi

Catalina = manufacturer

BJ06396 = cylinder serial number

M4002 = indicates Catalina

09-97 = original hydrostratical test performed in September 1997


S063 = cylinder used for Scuba with capacity of 63 cubic feet (when filled to its rated service pressure of 3000 psi)
* My gratitude to Odessa Stratton for editing and improving this article. *

Coming in July

Fill Station Operations: Does filling cylinders immersed in water make a difference?        

All images: Fred Stratton 


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