manual inflation of BCD

[LindaSSF]

I was certified in 1977, and my BC, a White Stag bright orange “horse collar,” only offered manual (oral) inflation. I used that BC for nearly forever & still have it, fully functional.
When today’s BCD’s with an auto-inflation attachment point came out, my friends & dive instructor saw it as a “waste of air”. We were diving steel 72s, so air management was always a consideration. By manually inflating our BC’s, we were “using” our air for our own metabolic needs, then using the exhausted, spent gas to inflate the BC.
Is there a real savings? Is it worth the bother?

 

[Lucas Cordina]

Well, if you're used to it, and you don't get overexerted by manually inflating your BCD, there are definitely benefits and you'll conserve air, though being perfectly honest, it won't decrease your overall air consumption by a substantial amount, still, every little bit counts, no?

(Was having a conversation with my instructor about this, and she's been diving since BC's were deemed as just an accessory, and a useful one at that)

 

[mala]

a 20kg bcd full at 40 m(unlikely) will have 100lts of gas in it.

sac rate 20lts/min is 100lts a min on the bottom.

so thats 1 min of gas on the bottom and about 2 mins at 15m.

 

[Scuba_Noob]

a 20kg bcd full at 40 m(unlikely) will have 100lts of gas in it.

sac rate 20lts/min is 100lts a min on the bottom.

so thats 1 min of gas on the bottom and about 2 mins at 15m.

True, you might save a minute or two. But if you exert yourself in manually filling your BCD, your SAC rate might just rise a bit for the next few minutes anyway, decreasing the 'savings'. Also, in exchange for a few minutes, I'd rather have the comfort and convenience of auto-inflating my BCD; I'm down there long enough already.

 

[captain]

True, you might save a minute or two. But if you exert yourself in manually filling your BCD, your SAC rate might just rise a bit for the next few minutes anyway, decreasing the 'savings'. Also, in exchange for a few minutes, I'd rather have the comfort and convenience of auto-inflating my BCD; I'm down there long enough already.

How would you exert yourself exhaling into the BC. Oral inflation is at most a slight inconvenience.

 

[Lucas Cordina]

How would you exert yourself exhaling into the BC. Oral inflation is at most a slight inconvenience.

Well, maybe exertion is the wrong term, but let's say you inflate a balloon, it's only natural that after filling it up, you take a few short breaths to compensate for the "effort" you've given in inflating it, even though the air you were blowing into the balloon was metabolised and used

That alone could decrease the gains from not using an auto-inflate (well, that's my two pennies anyways)

 

[stairman]

I wouldnt bother to manually inflate to save gas, but it is a good skill to practice occationally in the event of a sticking LP inflator.

 

[LindaSSF]

When I see new divers inflating thei bcds off the tank willy nilly, then dumping, then filling some more... I start thinking how much more conservative they might be if they were manually inflating. THEN, I think you might start seeing real conservation of gas!

Thanks for the math, Mala. Yeah - 1-2 minutes of additional dive time doesn't sound like much. Wonder how much is lost by the situation I just described? Wehen people tell me they had 35-40 minutes of dive time on a 80 tank at 30-40 feet, that gas has to be going somewhere! I'm hard pressed to think they worked that hard or breathed that fast.

 

[James R]

When I see new divers inflating thei bcds off the tank willy nilly, then dumping, then filling some more... I start thinking how much more conservative they might be if they were manually inflating. THEN, I think you might start seeing real conservation of gas!

Thanks for the math, Mala. Yeah - 1-2 minutes of additional dive time doesn't sound like much. Wonder how much is lost by the situation I just described? Wehen people tell me they had 35-40 minutes of dive time on a 80 tank at 30-40 feet, that gas has to be going somewhere! I'm hard pressed to think they worked that hard or breathed that fast.

I think proper weighting is more beneficial than worrying about oral inflation for the divers you mention here. If you're weighted properly you don't need to add/dump air over and over like that.

 

[Rich Keller]

I was certified in 1977, and my BC, a White Stag bright orange “horse collar,” only offered manual (oral) inflation. I used that BC for nearly forever & still have it, fully functional.
When today’s BCD’s with an auto-inflation attachment point came out, my friends & dive instructor saw it as a “waste of air”. We were diving steel 72s, so air management was always a consideration. By manually inflating our BC’s, we were “using” our air for our own metabolic needs, then using the exhausted, spent gas to inflate the BC.
Is there a real savings? Is it worth the bother?

It will save you some air but the bigger air savings will come from using the BCD as little as possible. If you weight yourself so you are neutral at the surface with a full tank then add enough weight to cover the difference between a full tank and the same tank at 500 psi you will be slightly negative at the bottom. In shallow water dives this amount of negative buoyancy can be over come by simply moving forward but with deeper dives suit compression would play a bigger role so you might need to put a small amount of air into the BCD. Using this method you would be more streamlined and able to use a smaller BCD. The site below will give you the difference between a full tank and the same tank at 500 psi for most tanks commonly in use today.

Scuba Cylinder Specification Chart from Huron Scuba, Ann Arbor Michigan