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kat_92

Demand valves

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Hey everyone,

for those of you that have an oxygen set up, and preferably have tried both a tank with and without a demand valve, can you educate me a bit? Does it make a difference in abort times, does it help save on oxygen in the tank, etc? 

I found a regulator that goes up to 25 lmp with a DISS fitting. The regulator I currently have goes up to 25 lmp as well. Now, I’m addition I need to actually purchase a demand valve? I found one on wtfarely for around $300. I know that’s the going price for these. Is it worth it?

thanks! 

Kat

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Demand valves can potentially save O2 when you are using high flow.  Since the O2 is only supplied when you inhale and not continuously dispenses at whatever rate you select.  Batch has given his perspective on this a couple of times.  There are demand valves available at times on eBay if you are interested.  Personally I don’t like it and prefer the continuous flow however I do use it when I have a small cylinder and want to save volume.  Remember breathing technique is as important as flow rate as you want to hyperventilate to get rid of CO2.  Thankfully its a rare time these days I get hit thanks to fungi.

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If 25lpm with a non-rebreather (NRB) mask is sufficient flow for you (sufficient that the bag is always full when you are ready to inhale using a fully effective breathing technique), there's no reason I can think of that your aborts would be faster using a demand valve.  There are small "studies" claiming greater effectiveness for demand valves vs. NRBs, but in those studies the people using the NRBs had flow rates of 15lpm, which might just have been too low for them. (Average abort times for people using the demand valves in one study was 12 minutes. I don't think that means much, since everyone has different results from O2, but 12 minutes isn't super-fast.)

I also have never seen how a demand valve would save any significant O2. With a non-rebreather mask, the O2 goes into the bag and you inhale it. All the demand valve does is to skip the bag part, so it seems to me that at the end of the abort you have inhaled very close to the same amount of O2, except possibly for some small leakage in an NRB system (or, conversely, getting a deeper inhale somehow from the DV might mean you'd use more O2 with the DV if abort times were the same).  If you got faster aborts with the DV, it clearly would save some O2, but I am not confident that that would happen.

That said, my daughter loves her demand valve system, in part because the mask is very cushy (not true with all DV systems) and I think maybe because she feels more in control in some way.  She's had it for many years. Her aborts have not been faster with it, as far as I can tell.

I'm not sure you can buy a DV valve from a supplier without a prescription.  I don't think you can.  The Ebay ones, when they appear, don't require a prescription.

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I have a demand valve, several 25 lpm regs and a 40 lpm reg. My advice is always this...if you have a proper mask like the ones we all recommend here and you can't "outrun" a 25 lpm reg with your effective breathing technique, a demand valve won't help your abort times. Now....what do I mean by "outrun". If you are constantly having to wait for the bag to fill you are outrunning the flow. If there is very little or no wait then you have enough flow for your technique and more flow won't be of use to you.

Now....for the sake of discussion you are outrunning your 25 lpm reg and would benefit from a higher flow rate there are several ways to get it. One is the garbage bag rig which some use but personally I don't care for. Another is the fabled demand valve or just a plain old reg with a flow rate higher than 25. As I stated above I have both. Each has benefits and drawbacks. My demand valve sits beside my bed at the ready for those night time wake up calls. It's easy to reach over, turn the tank on and start huffing. No thought to flow rates, fumbling with dials just grab it and go. To me this is where a demand valve shines. It's good in a car for the same reasons. It does conserve O2 because it gives you no more than you ask for. Drawbacks.....cost. They can be pricey. If money isn't too much of an issue, you believe the flow rate will be of benefit and you like what I've laid out here, go for it. 

But before you do, consider this..... A 40 lpm reg can be had for much less than a new demand valve. It will give most people all the O2 they can handle so abort times will be very close if not the same. Yes it does require more thought to dial in and you'll probably be adjusting it up and down more than a 25 but having that extra flow when you need it is great. If dollars are tight, consider this route.

If I were sitting on the couch watching TV and needed O2, I wouldn't step over one to get to the other....but for the reasons listed above each makes sense in their own way.

Bill

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Thank you all for the helpful responses. I think for now, I will stick with my regulator on its own. It’s something I’ll consider down the line though. 

Thanks! 

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