Mark 15 Maintenance Manual
Chapter Three : General Maintenance Of Systems
Section One : Maintenance Overview
It is not my intention to teach you how to dive one of these machines, only to give you some of the insight gleaned from diving, maintaining, and repairing these rigs over the last few years. You should pay very close attention to all the maintenance tips given in the next few pages. You should familiarize yourself with all parts of the unit, and refer to this document to help you better understand how each part works with each other.
I highly recommend as part of your training that you receive detailed information and hands-on experience in taking your unit apart, repairing what needs to be repaired, and putting it back together. This training should come from someone who is well acquainted with the operation and maintenance of the Mark 15 rebreather. Currently, I only know of about 3 or 4 people who fall into that category, outside the Navy - so be careful who you choose as an instructor.
With that said, I'll add this pearl of wisdom:
THERE IS NO BETTER WAY TO LEARN ABOUT THESE MACHINES THAN BY ACTUALLY DOING THE WORK ON THEM YOURSELF.
By developing a ritual of maintenance of your unit, you will increase your knowledge of it, and continue to enjoy successful dives with it.
FAILURE TO ADHERE TO A STRICT MAINTENANCE PROGRAM ON THESE UNITS COULD CAUSE A FAILURE THAT COULD KILL YOU.
I can't say it any simpler than that.
Section One : General Maintenance
Before each diving excursion, you should completely prep your rig for the upcoming dives. The following procedure is what I do each and every time I prep my unit:
Completely remove hose/mouthpiece assembly and clean thoroughly.
Completely remove center section and counterlung - clean both thoroughly.
Remove, clean and re-lube all o rings in center section assembly.
(General Maintenance - Contd.)
Apply thin coat of lube to counterlung surface.
Inspect all o rings in pressure assemblies.
Since my dive trips usually last 2 to 3 weeks, with up to 4 dives per day, I usually go a bit farther than the above list, and include the following:
Rebuild 1st stage regulators.
Remove/lube or replace o rings in Bendix connectors.
Remove/lube o ring located in counterlung overpressure relief valve.
Rebuild mouthpiece with new o rings.
Basically, let me give you my philosophy regarding rebreather maintenance:
First of all, your rebreather is a Life Support Device - that means that it is responsible for keeping you alive underwater. As I have said before, these machines can save your life in about 5 different ways, but can kill you in a dozen different ways as compared to open circuit.
I keep that fact in mind when I maintain my rebreather. Before a trip, I will completely tear down the unit, and perform all the maintenance listed above, like a religion. But once ON the trip, I hardly touch my unit at all, except to dive it. The reason is very simple: If you have done all the maintenance and preparation of the unit properly before the trip, you shouldn't have to touch it for quite a while, maintenance-wise. Naturally, you'll be drying out your absorbent pads after dives, and cleaning out the accumulated gunk that seems to live in your hoses, but other than that, you shouldn't have to do a single thing, except fill your spheres, and change your scrubber every so often.
Try not to become the kind of rebreather diver that constantly pores over his rig on a dive trip, attempting to catch up on maintenance that should have been done in the shop back home. First of all, working on a boat is a pain, and unless you carry a really large bag of spare parts and miscellaneous stuff, you're probably not going to have the right part for the job anyway.
The Navy did a good job for us, designing a very simple, hearty rig. We've made improvements on their design to make the unit more rugged, so it should serve you many years and many dives.
Section Two : Routine Maintenance
(NOTE: Your instructor may add to this list, depending upon their personal experience - at all times, take the advice of your qualified instructor).
The following is a description of routine maintenance that you should undertake at the end of each dive day:
1) Remove hoses/DSV (Dive Surface Valve) from rig - wash out hoses with some kind of disinfectant.
2) Remove cover of Center Section - remove absorbent pads - rinse them in disinfectant.
3) Allow hoses/DSV and pads to air dry overnight.
The following should be done after every dive trip:
1) Wash down rig completely while still assembled (close the DSV)
2) Remove hoses/DSV from rig - soak them in disinfectant.
3) Remove absorbent pads from rig - soak them in disinfectant.
4) Visually inspect all Bendix Connectors and cable assemblies. Look for any water intrusion, or damaged/worn o rings. Spray some contact cleaner/lube in the end of each cable - replace/re-lube o rings, re-attach cables.
Once again, I'll note that I go farther than this normally, including the removal of the Center Section, and Counterlung, with the Counterlung getting a thorough cleaning and re-lube as well.
NOTE: WHENEVER REMOVING THE HOSE/DSV ASSEMBLY, BE SURE TO RE-ATTACH IT PROPERLY, SO THAT THE INTAKE AND EXHAUST ARE LOCATED IN THEIR CORRECT POSITION - FAILURE TO DO SO, COULD RESULT IN INJURY OR DEATH.
If you are not sure which side is which, remember this: Put the DSV in your mouth and place your hands over the open ends of the hoses - remember You have the RIGHT to breathe - simply, that means the Intake should be on your Right side as you inhale, creating a vacuum against your hand.
Another Juergensen-ism is this: Whenever you are diving your rig, and can't recall which side the Oxygen Manual Add valve is on, just say to yourself Oxygen is the RIGHT gas to breathe... Got it? Good.
OF SPECIAL NOTE TO MARK 15 REBREATHER DIVERS!
There are many critical parts of your rebreather, but one stands out as a particularly vital part, the failure of which could go unnoticed by the diver during the dive, and potentially cause disastrous results. You should pay special attention to the following paragraphs.
Located inside your Center Section, you will find the Cannister Seal - this is essentially a big rubber band made of either an inner-tube tire, or natural rubber. This seals the Cannister from the rest of the Center Section, and prevents exhaust gasses from passing around the Cannister into the intake breathing loop.
The natural rubber bands that were original equpment on the Mark 15's had a very bad tendency to snap after installation. Often, this could happen long after they were installed, and the case closed. It occurs when the band becomes old, or is subject to contaminants, such as air pollution and solvents.
Most Mark 15 divers have replaced this natural rubber with a piece of a truck tire inner-tube. While not very elegant, this solution works quite well. Inner-tube rubber is very tough, and can last longer in service than natural rubber.
However, this band is vital to keep exhaust gasses from mixing with fresh air in your counterlung. Should this band break during a dive, the diver may be subjected to a condition known as Hypercapnia where CO2 laden exhaust gas is mixed with scrubbed air, resulting in a cycle where the overall CO2 content of the breathing mix increases. Hypercapnia can result in confusion, loss of consciousness, and even death.
It is recommended that this Cannister seal be replaced by the diver during Routine Maintenance at least every 3 months. Further, when not in use, the Cannister Seal should be removed from the unit and stored in a plastic bag to prevent relaxing of the rubber compound, and deterioration from air pollutants and solvents. Failure to follow this recommendation can result in severe injury or death.
Make sure to check this band frequently - in my opinion, it is one of the weakest links in the Mark 15 system, and should be treated with care and attention.
One solution to this problem has been addressed by a few Mark 15 divers, apparently with success: Essentially, you seal the Canister/Center Section using some UL listed Electrical Tape. This is very cheap, sticks well to both the stainless Center Section material, and the rubberized outer Canister hull. After the dive, you can then simply discard the used tape. Please be sure to consult your Rebreather Instructor regarding the best method to seal this critical area of your Mark 15.
Now lets move on to a discussion about how your rebreather works during a regular dive.
The Diving Home Page
Chapter One - The Mark 15
Chapter Two - Various Models of Rebreathers
Chapter Four - Operation
Chapter Five - Keeping it Working
Chapter Six - What to Look Out For - (Warning Signs)
Chapter Seven - Personal Philosophy of Handling Emergency Situations
The Final Word...
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