NIKONOS O-RINGS AIN'T JUST BLACK RUBBER BANDS (PART 1)
Text and Photos by Bob Warkentin
This is Part 1 of a 6 part series on O-rings. The problems we'll study are: (1) O-ring fatigue: when you apply grease, round black USED O-rings look just like round black NEW O-rings to most everyone until a flood happens, and (2) "O-rings" is not a simple topic if you are going to fully understand them, and learn to identify and use them correctly to keep your equipment from flooding. Sprinkled through this article will be photos of only some of your "user serviceable" O-rings, installed into their respective O-ring channels, showing a comparison between their appearance in a state of "new" vs. "flattened". By the time the series is completed, all "user" O-rings for all your Nikonos cameras, lenses and SB strobes and cables will have been shown, as well as some internal O-rings you can't get to.
All O-rings may look to you like thick black rubber bands or plain ole' common "hardware store" O-rings. Not so for Nikonos O-rings: there's a lot of science and technology that has gone into the development of the synthetic rubber (called either Nitrile, Buna-N, or NBR) for its end product uses. And, like everything else, there are "pros": abrasion resistant (opening and closing O-ring sealed areas to change batteries, film, etc.); chemical resistant (the gasoline, diesel and oil in the water at the back end of the boat won't damage the seals as we wait to re-board); wide temperature use range; and no oxidation when exposed to water; and "cons": these seals will take on a permanent "in use" memory (fatigue) of about 25-30% over time.
Almost daily, I have to answer that horrible "why" question: why did my strobe, camera and/or lens flood? The explanation generally involves fatigue to their rubber O-rings, or a combination of fatigue and their failure to remove contamination. Worst of all, everyone thinks that simply greasing O-rings keeps them good forever.
So, how do Nikonos rubber O-rings fatigue? Let me use a common rubber band to explain.
We get rubber bands free around our news paper or our door knob; sometimes we even have to buy them. New or used, we never think of them going bad. But, if you left your news paper in the closet for 6 months wrapped with a rubber band, surprisingly you would discover that this valuable little item had been permanently stretched out of shape and had lost its elasticity. True, we may have to twist it around something a couple of times more, and if it should break we can simply tie a knot in it to restore its usefulness, but it never seems to fail us if we really need it.
What really has happened during this 6 months is, unknowingly you have asked the rubber band to continuously do some form of WORK (that of holding the paper rolled up). In the process of doing this seemingly unimportant and not really requested WORK for you (because you knew where it was and had plans of using the rubber band for other purposes later on, you just forgot to take it off the day the paper was delivered), what has happened is that the rubber band has taken a "memorized" WORK shape based upon the size (WORK required) of the paper. Even if you now remove and save the rubber band, a year later it's still limp.
Another way of explaining this effect is that the news paper becomes a mold, causing the rubber band to be slowly and continuously "REMOLDED" to the exact size and shape of the rolled paper.
In short, the rubber has permanently given up its "ELASTICITY" by being "REMOLDED" during its process of providing you "WORK". It happened continuously, little by little, starting from the day that the rubber band was first put around the paper until the day it was removed.
Regardless whether we are talking about Nikonos equipment or a door at the house, everything that is designed to be opened or to be moved must have some space (be it ever so small) between it and the item to which it is attached or into which it is intended to function. No space, no movement!
Nikonos O-rings must be an "elastic filler", filling the space that must exist between movable things like the lens and the camera's casing, the battery cap and the strobe's casing, (for your door at home, you can put a rubber "filler" strip around it to reduce hot or cold air loss!).
Therefore, a Nikonos rubber O-ring is (1) an "elastic filler" (2) of certain chemical, environmental abrasion and compression resistant qualities that (3) must do the WORK of providing a force of sufficient elastic resistance between two items (4) greater than the maximum rated external force to which it is intended to be exposed (water pressure) (5) to provide sealing (prevent leakage).
NOTE: You better realize once and for all that O-rings, their properties, use and fatigue factors is really a science all its own. And, since O-rings keep your equipment from flooding, you need to understand them more than just putting on grease before diving. Also, these terms set the stage for the explanations of why your O-rings fail, and why user mistakes happen which lead to equipment flooding.
You bet! Every O-ring installed in your equipment is filling those spaces between the parts and are, therefore, under its MAXIMUM condition of WORK compression, whether during periods of storage or during diving. Sooner or later, they get flattened (remolded), regardless of how many dives you have made.
Oh, don't forget about those internal O-rings that you can't get to. They have been under continuous compression since the day they left the factory, and they get flat too (see Part 2)!
You've got to be kidding! Let me use a sandwich type cookie, consisting of two cookies with a cream filling, as an analogy for explanation. (Note: before you give me someone's "kidney bean" shape philosophy of O-ring vs. pressure, see Part 2!)
1. Just like you pushing one cookie towards the other, water pressure forces the camera to the lens and the lens to the camera.
2. As we force the cookies towards each other, we see that our pressure has forced the cream center to be squashed and it now oozes out to the sides of the cookies. The more force to each cookie, the more force on the cream center, and the more oozing. This would be what I call a "gasket type" of compression: full face-to-face sandwich compression like your "mask squeeze" phenomenon.
3. Now, let's call one half of the sandwich cookie the lens, and the other half the camera. Let's assume that the lens' O-ring (the cream filling) was designed to lay flat within and on top of the bottom flat face of the silver colored ring on the front of the camera (and not in the O-ring channel of the lens casing), and that the lens was somehow designed to be installed to the camera with the O-ring in this location (see photo 4). Thus, as water pressure forces the lens towards the camera and visa versa, the deeper you dove the more force (squashing) would be applied onto the O-ring lying between the two camera-lens cookies. If such was the design by Nikon, rated depth of the equipment would not be limited by the O-ring seal, but by crushing the metals of the equipment. If this "gasket" design were in a Nikonos, only then would it be true that water pressure did make the O-ring seals seal better.
4. What actually happens in the Nikonos from water pressure is that only the flat metal surface of the back of your lens is pressured against the flat metal lip in the floor of the silver colored lens mount ring on the front of the camera. Remember, ain't no O-ring there; it's in the channel of the lens (see photo 5). The water pressure just forces metal parts to metal parts!
1. We are all familiar with the 3-walled O-ring channel; it consists of 2 vertical walls (numbered 1 & 3) and a bottom or floor wall (numbered 2). Therefore, O-rings for Nikonos equipment generally compress and seal only between walls #2 (of the channel) and against the 4th wall of the O-ring environment (see closely photo 5).
2. 4th wall? What is this? True, it hasn't got a catchy name like O-ring channel, but it is just as important. In the case of the lens O-ring, this would be the vertical surface of the silver colored lens mount ring on the front of the camera into which the lens O-ring is compressed against. (For other areas like the door, etc., I think you can now figure out for yourselves which walls are #2 and #4.)
3. Water tight sealing by the O-ring is governed by the available rubber which extends above and beyond the lips of its O-ring channel. When the O-ring containing item is installed into another item, compression to the extending amount of the rubber by wall #4 forces the rubber against wall #2, thereby forming a rubber "filler" between the two items and water tight seal. (Walls 1 & 3 generally are not involved in the act of O-ring compression for "user serviceable" seals; they act only as guides preventing the O-ring from buckling! Remember this! See Part 2.)
4. Since it is the outer and inner edges of the O-ring which actually provides all of the water tight sealing between pieces of equipment, I'll call this form of sealing as being "edge" compressed for this article.
The degree of flattening may be slight, sometimes non detectable to the average person's eye; it can even be obscured by excess O-ring grease. But we can all recognize a flood. So, let's learn how to recognize a bad, flattened O-ring, other than through equipment flooding.
1. Since compression to Nikonos O-rings occurs between walls #2 & #4 of the O-ring environment (remember, walls #1 & #3 are just guides), it stands to reason that any and all remolding memorization (flattening) to the O-ring from compression will be easily seen and detected by comparing how much of the O-ring extends above the tops of walls #1 & #3 of the O-ring channel.
2. The easiest way to check for flattening of an O-rings is to compare two pieces of like Nikonos equipment, one with a known, brand new O-ring installed, to one with the O-ring in question. If the O-ring in question appears to be wider across the middle (squashed closer to walls #1 & #3) , not as round vertically, and does not extend above the tops of walls #1 & #3 of the O-ring channel equally as far as the new O-ring does, better replace it.
3. If you don't have a second item of like kind with which to compare, then you must rely on your "mind's eye". Examine the seal in question for its physical characteristics as in (2) above, then replace it with a known new seal and again examine its characteristics. If you can't really remember how the old seal looked like, then throw away the old and go with the new! Better safe than sorry.
Putting O-ring grease on a flattened O-ring is just like putting O-ring grease on a bald tire. Although the tire may look shinny and new, you still ain't got no traction on a wet street! You got to buy new tires (hint-hint!). More on "grease" in Part 2.
Are there other forms of O-ring fatigue? You Bet there are! Stay tuned to the next articles.
NOTE: Please, before you get the idea of storing your equipment in the closet without "user" O-rings installed, you better read Part 2 in the series!
Reprinted with permission from Bob Warkentin's Southern Nikonos Service Center, Inc.
9459 Kempwood, Houston, TX 77080 713/462-5436