Juergensen Marine
Mark 15 Maintenance Manual
Chapter Five
Chapter 5 : Keeping it Working
Section
1) Preserving a sealed loop
2) Preserving Gas Transport Integrity
3) Storage and Handling of Sensors and Sensor Wires
4) Proper care of Displays
5) Proper care of Cables
Keeping your rig in top condition involves a lot of work, but thankfully, only in short bursts. If you adhere to a regular schedule of maintenance, you can look forward to may successful hours of diving your unit trouble free.
The following is my suggestions for maintaining your rebreather at its peak.
Section One: Preserving a Sealed Loop
Making sure your loop maintains its integrity is not as hard as you would imagine, but it is surprising how few people do it.
Lets start off with the closest part of the loop to you - the Dive Surface Valve (mouthpiece).
The DSV is actually the source of most leaks in the loop. It's maintenance is good for a number of reasons, not the least of which is the fact that it spends most of its life in your mouth.
Since the DSV lives in your mouth, it, by its very nature, accumulates most of the goobers and gunk that you exude from your bodily orifice. This can have a detrimental effect on the “O” ring seals that live inside the DSV. As such, I completely disassemble and rebuild the DSV after every dive trip. I don't mind saying that I am constantly amazed at what comes out of this thing...
You will go a long way toward preserving the integrity of your loop by taking the time to rebuild your DSV periodically.
The second part of the loop that needs attention is the hoses. These are rather simple devices, and do not represent a very complicated sealing issue. I generally will re-seal the hoses after a thorough cleaning by using only a tiny amount of lubricant over the inside diameter of the ends of the hoses. Too much, and you run the risk of the hoses squirting out from their connectors when pulled. If you use NO lubricant, they will seal fine, as well, but you then run the risk of “bonding” of the rubber to the mating surface of the connector, thus lowering the life span of your hoses themselves.
The last part of the loop is the Counterlung. The Counterlung is actually much more complex than what appears at first glance. It consists of several parts, including “O” rings that help seal it from the outside water.
The Counterlung is made of a particularly pliable rubber compound that easily binds to the stainless steel center sections used in the Mark 15 rebreathers. Because of this, and the sensitivity to other airborne compounds (such as hydrocarbons emitted by gas and diesel engines), I always coat my counterlung with a thin film of Silicone lubricant before re-installing on my Center Section. I personally don't believe that the Silicone represents a fire-hazard in the Oxygen environment of the Center Section during diving, so I don't waste my time with O2 clean lubricants for this task. However, you may wish to use Crystolube, or Halocarbon if you are an O2 clean purist.
Inside the center part of the counterlung is where the Overpressure Relief Valve lives. I make a point to always take this apart when cleaning the Counterlung, since that is the place where many expelled goobers make their way into the open sea. Lung-goobers seem to be the worst, and can cause sticking of that valve. All it takes is a few minutes to take it apart, clean the valve parts, and re-lube the “O” rings. This will ensure proper action throughout its life span, which can be many, many years.
Section Two: Preserving Gas Transport Integrity
The Gas Transport of the Mark 15 is comprised of several stainless steel tubes, hoses, and valves, each of which can experience problems over time. You can prevent these problems from occurring through good maintenance of the system as a whole.
One thing you will notice, if you are diving in salt water, is that many of the couplings will show signs of rust on occasion. I'm told that this really isn't rust at all, but it is red, and looks like rust to me. It is caused by the “bi-metal” reaction that takes place in the presence of salt water. Even metals that are identical in composition (such as the 316 Stainless used in the Mark 15) can exhibit this reaction, due to minuscule differences in their metallic composition (such as would occur in different lots of the same grade Stainless coming from two different foundries).
Whatever its cause, I don't like to see any rust on my machine. If necessary, I will disassemble the tubes from their fittings, and polish the “rust” off with my Dremel, using a stainless steel wire brush attachment.
After polishing, I'll give the OUTSIDE of the fittings and tubes a spray of pure Silicone to help prevent this build-up in the future. So far, it seems to work great.
The next part of the Gas Transport that needs attention is the Manual Add Valves, located on either side of the unit. I don't recommend you attempt rebuilding these unless you have a good working knowledge of valve rebuilds, and understand your unit thoroughly. Why? Because they are a pain in the ass to remove, repair, and align correctly once you are done.
However, I really believe that after 100 hours of dive-time, they should be removed and rebuilt, regardless of the difficulty.
I've been working on Manual Add Valves for a long time, and many of them had some clogs that blocked the injection port, just behind the seat.
Just to experiment, I pumped 300 psi behind these blockages, and they would not budge.
Obviously, this blockage could cause some problems if it occurs at the wrong time.
So: As part of your maintenance of the Manual Add Valves (should you be the one who rebuilds them), I recommend you do what I've been doing with all of them - Simply insert a .042" diameter drill (that's right - point oh four two - this is one small hole) through the orifice to make sure any debris is clear - then blow the valve body out with some compressed air.
Now, the filters in the 1st stages, as well as the 60 micron filters in the pneumatic lines are supposed to stop garbage like this from making it's way to the Manual Add Valves, but
If your valves are in really bad shape, you can order new ones from SwageLok (Part #SS-1GF2-A {note: The old Military # was "SS-0GF2-A" I don't know why - they have an "OG" series, but the outlets are smaller than 1/8th NPT which is required} ). They're about $45 each, which isn't a bad investment if you're the type that doesn't want to mess with the guts of one of these.
Two parts of the Manual Add valves require special attention: First is the internal spring. Most of the springs I come across have corroded and broken. Replacement springs are available, once again from your local SwageLok dealer. They are cheap, and easy to replace. The second, is the small diameter hole
Section 3: Storage and Handling of Sensors and Sensor Wires
Storage and handling of the sensors is a hot topic amongst rebreather divers. The maintenance of the sensor wires is a topic that I am very familiar with. I will give you the different opinions of the former, and my authoritative view of the latter.
Sensors: Oxygen sensors, more correctly known as Hyperbaric Sensors are essentially batteries that run on oxygen. The typical Oxygen sensor is comprised of an anode, a cathode, some reactive medium, and a gas permeable membrane for Oxygen to pass through. The Oxygen sensors in the Mark 15 are made by BioMarine Instruments. Inside the sensor, an anode of spun lead sits in a bath of Potassium Hydroxide (KOH). Across the KOH lies a cathode screen which is gold plated. The KOH soaked lead reacts in the presence of Oxygen, and releases electrons, which flow across the medium to the cathode. This flow results in direct current voltage flowing out from the sensor. The amount of electrons being released is (pretty much) linear with the amount of Oxygen present. Therefore, the higher the Oxygen partial pressure, the higher the voltage output as expressed in mV DC (millivolts, Direct Current).
Because this reaction slowly decays the lead and gold on the anode and cathode, the sensors have a limited life span, usually about one year. This has resulted in many different ideas as to how they should be stored.
Most all rebreather divers agree that the Oxygen sensors should be stored in separate containers when not in use. I personally store mine in small Tupperware containers that measure about 2” in diameter, and about 2 1/4” high.
Some divers believe that the containers should be flooded with Nitrogen, or Helium when the sensors are put away, to eliminate the presence of Oxygen as much as possible. My understanding of this practice is that they get about a year of service out of the sensors that way.
Other divers believe that the sensors should be stored in the refrigerator. I understand that using this particular method, they get about 12 months of service life out of the sensors.
I imagine that if you were to flush the sensor containers with Helium, and then store them in the refrigerator, you might expect to get as much as 365 days of service life out of them...
As you can see, you're gonna get about a year of life out of the sensors before they die...
One important thing to remember is that the sensors should be marked as to their position in your rig, i.e. “#1, #2, and #3” you should also put the date of installation on each sensor so that you can keep track of how old a particular sensor is, and when it is likely to need changing.
It is important to keep the sensors numbered because mixing of the sensors can throw the calibration of your Electronics and Secondary Display way off.
I personally keep a small data tag in each sensor container where I write the output voltage of each sensor (measured in air) upon storage, and removal from the container. I have found that this gives me a good idea of the “health” of each sensor, and helps me to determine when its gonna die.
Whatever method you decide upon, the one thing you really want to do is somehow, somewhere keep track of the sensor readings as the one year life progresses. And don't mix `em up - Sensor 1 is always in Position 1, etc.
The Sensor Wires
The sensor wires in the Mark 15, 15.5, and 16, are the single weakest link in the entire system, as far as I'm concerned. And I'll tell you why:
Inside the Center Section, there is the Sensor Bridge (which, surprisingly, holds the Sensors). Outside of this bridge, you will see six wires, three red, and three black. These are the wires that carry the voltage output from the Oxygen sensors to the Electronics, via the “Horseshoe PC Board” and Bendix Connectors.
Now, if you take your Center Section out of the rebreather, and remove your Counterlung, you will see the area where the “Horseshoe” board lives. It is epoxy sealed. And herein lies the problem.
The Sensor Wires run through small holes opposite the Sensor Bridge, and pass directly into the Horseshoe PC board. These holes are epoxied as well. The wires are typical Mil-Spec wires, i.e. 22-25 awg wire, silver plated. Silver plating wires is a big thing with the Military. As many of you know, Silver is by far the best conductor of electricity - even better than Gold or Copper. For the millivoltage coming from the Sensors themselves, Silver makes a lot of sense. However, Silver is notorious for corroding.
The wires that lead from the Sensors to the Horseshoe Board are very sensitive to salt water and salt water spray. Once they have been exposed to salt water, their days are numbered. This is not fiction, but fact. Eventually, every Mark 15, 15.5, and 16 out there will have these wires go straight to hell. They get what I call “Creeping Necrosis.” Essentially, the corrosion will begin near the end of the wire, and slowly creep down the length of it, under the insulation. This will go unnoticed by you. And one day, you will pay dearly for it... (sounds like a bit of a horror movie, eh?)
When the Sensor Wire finally gives out, it usually does so by breaking. You'll notice that you don't get a reading from a particular sensor. This usually happens when you are installing the sensors in preparation for a dive. You will examine the wires, and find that one of them has broken. The usual site for this break is right at the end of the wire, where it is epoxied into the Center Section.
I once watched a good friend of mine dig with a dental pick to try and expose 1/64th of an inch of wire right at the epoxy to try and get enough wire to solder on. It was a sad sight...
So - what can you do? Well, quite simply, you can try to keep these wires from coming in contact with salt water. I suggest that you use a good corrosion prevention spray, like “Caig Super Gold” or something equivalent on the ends of the wires. Also, try not to let too much water into your loop.
And what if your wires break? Basically, you're screwed. Sorry. You will then have to have the old Horseshoe Board machined out, and a new one put in its place.
After seeing my fellow rebreather divers go through this horror, I took pro-active steps, and replaced my entire Horseshoe Board assembly and modified the way the Sensors hook up, to eliminate this problem from ever happening to me. It took me 2 weeks of work, but I got it done. If you want to know how to do it, you'll have to pay me huge sums of money, and walk my dog for a week...
Section Four: Proper care of Displays
The Primary and Secondary displays are rather rugged devices, that shouldn't require too much attention from you during their lifetime. However, some folks pay some additional attention to them, which you might want to follow.
The most fragile of the two displays, is clearly the Secondary. Not only does it have a delicate meter inside, but also a Bendix Connector on the end. I've already addressed how you should care for your Bendix Connectors, and the same applies to the Secondary.
Many divers like to keep the Secondary separate from the rest of the rig, usually kept in a padded case. This is a good idea. It's not an idea that I adhere to, but I have all the parts necessary to rebuild one of these, should I trash my unit.
Remember one thing about the Secondary: There are no spare Secondary Displays out there. So, the likelihood of you ever getting a replacement, or a spare, is highly doubtful. So you should take care of it.
The Primary Display needs very little maintenance. The only thing that usually goes wrong with them is that the bulbs can burn out. Usually the “O” bulb. Replacing these bulbs is no walk in the park, either. If you aren't good with electronics, and small part soldering, don't try to replace it yourself.
You can also replace the light bulbs with LED's (Light Emitting Diodes). I know one diver who did this, and is quite happy with it. However, he had to factor in
Section Five : Proper Care of Cables
The Bendix Cables found in your rig are extremely valuable. You won't find this out until you have one go out on you - then you will search fruitlessly for a spare, and eventually pay someone a fortune for a replacement. You can avoid this pain and suffering by maintaining your cables regularly. They are extremely robust cables, and don't require any attention when in use, but between dive trips, you should take the time to keep them in top shape.
Essentially, the only maintenance that I ever give my Bendix Cables is a thorough cleaning of the connector attachment nuts (inside and outside), cleaning of the connector bushing (which is located on the inside of the connector attachment nut) and a good spray of Caig “Pro-Gold” contact cleaner/lubricator.
By far, the best tool for cleaning just about everything on a rebreather is a Dremel Moto-Tool. I happen to use the battery powered units for most jobs, and the AC powered unit for heavier stuff on the bench. You'll need the Stainless Wire Wheel attachment, and the Straight Wire Brush attachment for the task.
First, I take the Stainless Wire Wheel, and clean the outside of the Connector Nut (the ring that you rotate to screw down the Bendix Connector). I then switch to the Straight Wire Brush attachment which fits nicely inside the gap between the connector itself, and the inside diameter of the Nut. I clean out any corrosion build-up (the green colored stuff that comes from the Brass Nut corroding). I then make sure to pass the brush around the Bushing (which is the smooth looking round surface just behind the connector itself).
The Bushing forms the seal with the captured “O” ring in the Bendix Bulkhead Connector, so you REALLY want to keep that clean and free of debris.
I then pass a Q-tip around the inside of the whole assembly to remove any dust or particles.
What I do next is a 2 step process : First, I spray the Caig Pro-Gold into the female connector plugs, so that it fills them up. Holding the connector perpendicular to the ground (so the Pro-Gold doesn't run out), I spray the entire connector assembly with 100% pure Silicone spray. You don't really want Silicone inside the connector plugs, so filling them with Pro-Gold first, keeps out any silicone spray that might get inside.
Once that is done, I verify that the “O” ring in the Bendix Bulkhead connectors are good, replace them if necessary, and re-install the cable. Try not to leave your newly cleaned cables lying around the garage. You also don't want to leave your Bendix Connectors left exposed either.
True Story: A friend of mine once had another fellow install a new set of electronics in his rebreather. My friend (of course) didn't bother to inspect the newly installed electronics (which weren't new themselves, they were a “loaner” that had sat on the fix-it guy's shelf for a while). During the first dive, he noticed his Primary display going wacky. He figured he had a flood in his battery compartment.
After exiting the water, he found that there was no flood. So he decided to disconnect the cables from the electronics pod to check the cables themselves. When he removed the Primary Cable from the Electronics Pod, he discovered a very large Cockroach, impaled on the 13 pins sticking out of the Primary Bendix Bulkhead connector. The roach had evidently ran in there to hide from the fix-it guy, and got impaled for his troubles. His bodily fluid managed to short out the cable connectors, and my friend lost a pin from the bulkhead side of the connector assembly, rendering the connector useless.
Chapter Two - Various Models of Rebreathers
Chapter Three - General Maintenance of Systems
Chapter Six - What to Look Out For - (Warning Signs)
Chapter Seven - Personal Philosophy of Handling Emergency Situations
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