Positive pressure valve for Ocean Reef?
- Thread starter robinzon
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robinzon:
You can purchase the necessary conversion parts to make your mask a positive pressure mask. I think it is simply a new air valve that operates effeciently at a pressure of 60 PSI. However, I think the best solution is to send it to OceanReef through your local dealer to have the conversion made. Thanks.
Phil Ellis
FFMDiver:Most positive pressure masks simply insert a piece of plastic in the second stage that pushes on the diaphragm causing a slight free flow. Maybe you can just push in the button with your finger...same thing...
It's not quite that simple. Although it is easy to confuse positive pressure with freeflow, they're not the same. The only positive pressure mask used in diving is the Interspiro Divator MKII. It comes it two versions, the other being the demand regulator. Both give you gas only as you ask for it. Positive pressure is created by the balance between a pair of springs, one being the counter pressure spring and the other the inhalation or sealing spring. To maintain pressure inside the mask a sealing disc is used to seal in the slight additional (positive) pressure. The counter pressure spring serves to maintain this pressure as well. Any mask that simply has a mushroom valve can't maintain positive pressure. In the case of the Ocean Reef, the restricted exhaust, I suppose, could be argued to maintain positive pressure. It's function is to prevent free flow if the diver is inverted. If a mask is positive pressure, it will freeflow when not sealed on the face when out of the water. Positive pressure is a feature designed for SCBA applications. It was never really intended for diving, although it works. When you're submerged, the water has more influence on the regulator than the springs.
MntDiver, a very insightful reply, thank you I know that GA makes the positive pressure version I never knew the mechanics of it though I thought as much...I guess indeed by purging the mask a bit you can make it a positive pressure mask.
Phil, I am not sure where you got your information but I am pretty sure the Ocean Reef themselves do not manufacture a PP version of the mask I thought it was an aftermarket conversion though someone might of been pulling our leg... who knows
I would love to see the picture of the positive pressure valve, I am still unclear since it makes sense for a mask to hive a slight freeflow as otherwise I don't see how the pressure is regulated/transmited from inside the mask back to the diaphragm in the second stage ?
Phil, I am not sure where you got your information but I am pretty sure the Ocean Reef themselves do not manufacture a PP version of the mask I thought it was an aftermarket conversion though someone might of been pulling our leg... who knows
I would love to see the picture of the positive pressure valve, I am still unclear since it makes sense for a mask to hive a slight freeflow as otherwise I don't see how the pressure is regulated/transmited from inside the mask back to the diaphragm in the second stage ?
mntdiver:
robinzon:
It's actually pretty easy, of course it helps if you know what the inside of the Divator regulator looks like. Refer to the link below.
The counter pressure or sealing spring in the regulator applies pressure to the sealing disk. This seals the exhaust to maintain an approximate 1 to 1.5 inches of water column of positive pressure inside of the mask. For a little background, inhalation and exhalation pressure of a regulator is measured in inches of water column by a magnehelic. Next time you're sitting in a restaurant, take your glass of water and your straw. Now either gently blow into the straw or suck on it, the level of water that you either push down or pull up is the measurement equivalent to your exhalation or inhalation pressure. When you push the water down an inch to an inch and one half, you have your exhalation pressure and vice versa. There, you have a rudimentary magnehelic.
As you observed, the regulator is designed to free flow if it's not sealed on your face. This is the mechanism that maintains clean air inside of an SCBA should the seal be violated for whatever reason while in a toxic gas environment. It displaces any bad gas, hopefully before the wearer inhales anything harmful. Again, this was designed for toxic gas environments. The exhaust of a Divator is through the center of the diaphragm. The spring loaded sealing disk seals over the floating edge of the diaphragm, over the exhaust in the center. When you seal the mask on your face, the counter pressure (sealing) spring is in effect, pushing down on the lever of the regulator, causing the free flow. This inflates the pressure inside of the mask, pushing out on the diaphragm with the spring sealed exhaust to the point where the lever is allowed to relax somewhat and stop the free flow. Now you have a mask with an approximate 1 to 1.5 inches of H2o sealed in the mask. With a properly adjusted and well fitting mask, the regulator will now function as a demand regulator, giving you gas only as you ask for it (inhale). Yet, if you interrupt the seal, it will free flow again. As stated earlier, this is describing how it functions in air. Take this mask into the water and the dynamics change considerably.
I could go on about positive pressure verses demand regulators. Ill have to leave that for another time though.
Here's a link to an exploded view of the regulator, let me know if this helps.
http://www.oceantechnologysystems.com/aga-exploded_gold_noprices.shtml
robinzon:
I clearly mis-read and mis-spoke. I was thinking completely of the low pressure, constant flow adaption they offer. That is what I described, but I incorrectly called it a "positive pressure" adaption. To my knowledge, they do not offer an upgrade to make the mask maintain a positive internal pressure. Sorry and thanks.
Phil Ellis
All of the explanations above are correct, but do not really describe why the company would want to produce a positive pressure full face mask. The simple fact is that this is required under the OSHA regulations for self-contained breathing apparatus used in atmospheres that are "Immediately Dangerous to Life and Health," or IDLH. In order for the Ocean Reef NIRA to compete with other SCBAs for the fire fighting market, they must produce a positive pressure version. The Interspiro Divator MKII is about the only other mask that can be used in this duel capacity (diving and as a fire fighting SCBA). Other SCBA units have problems with free flow (regulator at the belt means high free flows in some position in the water) and extreme visual distortion while underwater (because of the curved facepiece lens). I tested a Scott SCBA in the 1980s for use underwater, and wrote it up in NAUI News, that it is completely unacceptable underwater, as it would cause a visual distortion that could lead to vertigo it was so bad.
This has advantages to a diver in some applications. One would be when diving in highly contaminated water, when you really don't want any of the water to penetrate into the full face mask, and possibly be either inhaled or ingested. The other would be for diving in radioactive environments (such as some places in Hanford), which has occurred in the past.
For regular diving, having a positive pressure (or pressure demand) mask can have an advangage, but it would be minor. Basically, it increases the exhalation resistance of the mask by a small factor in order to exhale against the positive pressure established to ensure contaminants do not enter the mask. The disadvantage is that if the diver has a beard, that diver would be unable to maintain a seal, and the mask would leak air very badly (beards are prohibited for SCBA users).
SeaRat
This has advantages to a diver in some applications. One would be when diving in highly contaminated water, when you really don't want any of the water to penetrate into the full face mask, and possibly be either inhaled or ingested. The other would be for diving in radioactive environments (such as some places in Hanford), which has occurred in the past.
For regular diving, having a positive pressure (or pressure demand) mask can have an advangage, but it would be minor. Basically, it increases the exhalation resistance of the mask by a small factor in order to exhale against the positive pressure established to ensure contaminants do not enter the mask. The disadvantage is that if the diver has a beard, that diver would be unable to maintain a seal, and the mask would leak air very badly (beards are prohibited for SCBA users).
SeaRat
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