Jump to content


  • Content Count

  • Joined

  • Last visited

  • Days Won


Everything posted by diverdoug1

  1. YES!!!! The Dew point = the point where relative humidity is 100%. (THAT is by definition). As temperature increases in the housing, the dew point (which is the point where the housing air is saturated with water, which is also 100% relative humidity) INCREASES. If you take a housing at near dew point (say relative humidity of 99%), and cool it, the dew point decreases (and the relative humidity reaches 100%)............CONDENSATION FORMS! Then as the camera warms the interior, the dew point increases/relative humidity falls, and the fogging dissipates.
  2. Wrong again Fogging ONLY occurs when the dew point (100% realtive humidity) is reached at the air / surface interface. The "dew point theory" describes ALL cases of fogging/condensation formation. This is decreased by 1. decreasing the water in the housing atmospere via vauum / dessicant/ only opening in a dry environment 2. decreasing the pressure on the housing (thereby decreasing relative humidity / increasing dew point)
  3. Now youve got it! Yes, The tempaerature of the room you prep in is not an issue once the sealed system reaches temperature equilibrium at the dive site. All that matters is how much moisture that is trapped inside your housing. The less moisture in the housing atmosphere, the less it will tend to form a condensate if the housing is plunged into cool water. This is why the decreased pressure are and decreased trapped water molecues are helped by the vacuum system,, and why starting with drier air and dessicants help.
  4. Preparing in an aircondition cabin is actually better, but ONLY if you seal the housing before going into the hot humid air and KEEP it closed. If you go outside before you close the housing, or open it breifly once you are outside, you are screwed. The hot humid air comes in contact with the cool surface of the camera lens and inside of the port, and condensation occurs.. If you have the need to open the housing at any time other than when you are in airconditioned, dehumidified conditions, it is better to leave everything outside, so the surfaces of the camera and housing are warmer.
  5. They are one and the same, the vapor is the gas. The air contains water molecures which come out of the gasseous state and condense on the cool surface as the air is cooled, causing the relative humidity of the cooled air to reach 100% (dew point) and the condensation forms. This is the function of a common dehumidifier. Humid air is drawn over cooling elements, which causes the air to cool and deposit some of its water molcules on the cooling surfaces (condensate), which is collected in a drainage pan, The expelled air will have less water molecules per unit volume. I think you are getting hung up on the term "relative humidity"..It just means at a given temperature and pressure, how much water the air is holding compared to how much it CAN hold before reaching dew point.. As temperature increases and pressure decreases, the air can hold more water. As temperature decreases, and pressure increases, the air can hold less air. If the temperature in a room is 75 and the air is half way to dew point in the amount of water it can hold, the relative humidity is 50%. If you warm up the room to 90 degrees, the air will be able to hold more water, so the relative humidity will decrease, even though the amount of water in the air has not changed. This is why a hair dryer works. The heated air now has a low relative humidity, and can hold more water (think thirsty air) and can evaporate the water more readily (the oposite of a dehumidifier, you are actively putting water vapor in the air.
  6. Actually no, the camera heating up inside the housing will DECREASE condensation in the camera. The hot camera heating up the inside of the camera will decrease the realtive humidity (meaning that any condensate that has formed on the walls of the housing will find it easier to evaporate). You have used the term "dew point numerous times, this term just means 100% relative humidity.
  7. Your wrong again sorry to say. Relative humidity has nothing to do with the gas being a defined volume. In fact when you use the term "dew point" this is just when the relative humidity reaches 100%. Condensation occurs on a cold surface because the surface cools the air that is against it to a temperature where the relative humidity increases to 100% and the dew point is reached, then a condensate forms.
  8. This really depends on the conditions indoors and outdoors. Prepping the camera in the coolest, and driest conditions possible will be best. So inside with the A/C running would be prefferable to outside on a hot, muggy day. A cold crisp winter day outside would be preferable to prepping inside a warm house with a humidifier. Also, if you choose to use dessicant packets, you need to put them in your sealed housing well in advance of the dive, because it tikes time for them to absorb the water vapor in your housing.
  9. If you have no issues understanding Dalton's law, you should be OK with understanding Boyle's law. In the non-fantasy world your above post is simply nonsensical. Barring pixie dust, leprechaun's tears, and mythical weather sensors, decreasing the pressure in a vessel will decrease the relative humidity and inhibit condensation formation. The manner in which the decreased pressure occurs is irrelevant, all that matters is moles of gas molecules per unit volume. This is not conjecture but fact delineated by the laws of physics. If you don't like that your position is incorrect, then shake your fist at God and the heavens above, or write a nasty letter to Robert Boyle, John Dalton, and perhaps Isaac Newton. Q.E.D.
  10. I agree, we should keep this discourse civil, so that we may continue the discussion unfettered by moderation. Now, please answer the question, how do you propose the system be compressed and decompressed in the instance where you state "If this was a closed system being compressed and decompressed I would not have any issue agreeing that pressure increase changes humidity levels"? Increasing the volume of a sealed vessel by X% will yield the exact same internal composition as decreasing the internal fixed volume vessel's pressure by X%.
  11. When you said "well that is somewhat scary indeed" was that an insult? Regardless of that, to answer your previous post, when you say "if this was a closed system being compressed and decompressed I would not have any issue agreeing pressure increase changes humidity levels" WHAT IS THE DIFFERENCE???? If you take a fixed volume vessel at 1 atm, and apply a vacuum to .5 atm it will have the exact same internal composition as a closed variable volume vessel which starts at 1 atm and doubles its volume. Those are the only 2 ways that you can decompress a temperature constant system. 1.increase volume, 2.remove contents. When you posted the above quote regarding the closed system, how did you proposes the system be "compressed and decompressd"?
  12. "I would have thought you could have logically solved this by just looking at extremes" Indeed Watboy, but there is the rub. Sometimes logic falls upon deaf ears. "Knowledge and truth may be within us without judgment, and judgment without them; but the confession of ignorance is one of the finest and surest testimonies of judgment that I know" Michel de Montaigne,
  13. Doubtful, Interceptor, you have just agreed that dew point temperature will decrease as you create a vacuum, this means that the realtive humidity decreases BY DEFINITION. So you CAN derease the relative humidity with a hand pump. Q.E.D.
  14. Another good illustrative example is if you put a cup of water in a vacuum chamber, and pump it all the way down, it will start to boil at room temperature. This is the condensate (water in cup) going to a gasseous state. Once the vacuum is removed, condensation forms on the walls of the chamber.
  15. I watch the relative humidity INCREASE in the chamber with every treatment. I have supervised 2 treatments already today. I will certainly post is the converse happens for any remaining treatments today, and I will also let you know if the sun decides to set in the east today.
  16. A dehumidifier works by drawing air across cooling elements. Saturated vapor pressure is directly proportional to temperature. Since Relative humidity = partial pressuer of water / saturated vapor pressure of water, the relative humidity jumps up and condensation forms in the unit. A dehumidifier could also work by compressing the air, causing condensation to form in the unit. BTW, I monitor the relative humidity in a hyperbaric chamber on every treatment. I do this multiple times on a daily basis.. Interceptor is simply misinformed OR he has been very successfully trolling us. I think the latter is more likely.
  17. If you start with a relative humidity in your housing at 100% at sea level, and pump the housing down to negative 5 inches Hg, the relative humidity in the housing will be about 85%. Continue pumpung down to negative 10 inches and the relative humidity will be about 70% at constant temperature. Interceptors above statement that compressing the air having a drying effect is completely wrong. Relative humidity = partial pressure of water vapor / saturated vapor pressure of water.
  18. It was not my Wikipedia link, but I did read it, and the example you mention assume a constant dewpoint. That is not hte case in a housing as you evacuate its contents. You do make a chamber less humid by definiton as you evacuate its contents. Given a fixed temperature, relative humidity in a vessel will be directly proportional to the partial pressure of the solute vapor. As pressure in a vessel decreases, the partial pressure of that solute gas, and thereby the relative humidity of the solute gas will decrease.
  19. Interceptor, I am a hyperbaric physician , so what would I possibly know about vapor pressure? Or o-rings for matter?
  20. Condensaton occurs when a partialy saturated gas is cooled or compressed to the point where the molecular density of the solute gas molecules reach the maximum threshold. Decreasing the the molecular clusters in a given volume (if you pump the housing down to about negative 10 inches Hg the decrease in molecular clusters is about 30%) will allow a greater degree of compression or cooling prior to reaching the condensation threshold. So YES, a vacuum system can decrease internal condensation issues. For illustration, if you take a volume of gas which is very humid (near saturation) and compress it (via like gas injection) in a pressure vessel, condensate will form on the lining of the vessel.
  21. Both would magnify, but additional cropping decreases your resolution. Or are you talking about the inherent crop of using a DX sensor? Just to be clear, the Tokina 10-17 will get vignetting if you were to use it on a full frame sensor.
  22. "My thought that the creation of negative pressure at the surface might make it less likely that the seal created by the O ring would be compromised by the water forces" Draq, your thought is correct. Preloading the o-ring (even with a low negative pressure) will suck it into it's sealing position against the intersection of the two mating surfaces. That is how an active sealing o-ring works. A very high negative pressure which "locks" the mating surfaces in approximation is not necessary for this to occur. The normal operational vacuum for the Nauticam system is more than adequate for this sealing to occur. Regardless of the one dissenting incorrect opinion.
  23. The op did not ask if he could hit the release button, and no one said he could. The button has nothing to do with it. O-ring seating can be dislodged even with the mating surfaces in place without adequate preload. Hitting the release button uncouples the mating surfaces. Allow me to make an analogy to clarify this for you. You are standing in your garden wearing your scuba mask. The mask strap is adjusted lightly on your face so that it produces a watertight seal when you gently dip your head in the water. If you shoot your garden hose nozzle at the area where the mask meets your face, water will shoot in, but if you suck in through your nose, the increased negative pressure may prevent the leak. If you cut your mask strap (hit your red button) the mask will fly off. Admittedly, this analogy does not address the way that an active seal o-ring preloads, but may help you with an intuitive feeling for what we are trying to explain to you.
  24. No interceptor, you said it would "make no difference", which is incorrect! No system is a "blanket insurance policy". Had you stated that, no one would have argued with you, but that is NOT what you said. If you are modifying your opinion, fine. Regardless of your opinion, even if a port does not become dislodged, water intrusion can occur by blow-by in a low preload state. That is why aggressive drying with high pressure air can lead to water intrusion after a dive.
  • Create New...