Sidemount Power Inflation

[Bubble_blower87]

Just curious about whether sidemount rigs use power inflation? If so what happens when one tank runs out? Obviously you could manually do it but is that the only option?

 

[Sidemount_Stu]

I assume from your question that you're new to Sidemount... or just enquiring without any experience in it as yet?

Your cylinders should never run out...... when sidemounting, the diver does not breath one cylinder to empty then start on the other.... the 2nd stage regulators are swapped throughout the dive such that the gas is used across both cylinders and they are kept at very similar levels at all points throughout the dive.....

I hope this helps you to understand?

 

[Bubble_blower87]

I assume from your question that you're new to Sidemount... or just enquiring without any experience in it as yet?

Your cylinders should never run out...... when sidemounting, the diver does not breath one cylinder to empty then start on the other.... the 2nd stage regulators are swapped throughout the dive such that the gas is used across both cylinders and they are kept at very similar levels at all points throughout the dive.....

I hope this helps you to understand?

Sorry and yes I am new to diving in general. I am just kind of addicted all of a sudden and letting my curiosity get to me. I wasn't thinking but yes I remember that we keep 500psi minimum in our tank during back mount, I should have assumed the same for sidemount. I guess then that only one tank is used as the inflator?

 

[Sidemount_Stu]

Yes one for wing inflate the other for Drysuit inflate.

 

[Bubble_blower87]

Yes one for wing inflate the other for Drysuit inflate.

Well that clears it up for me thanks man.

 

[tbone1004]

unless you use the weird UTD Z-system which is an equipment solution to a skills problem. Inflating BC's doesn't take all that much air.
Let's think about it this way.
1cf of water weighs 63/64lbs.

We'll look at worst case scenario, so say you're using one of the big wings, so the Nomad XT with 50lbs of lift. You should be orally inflating at the surface, but even if you power inflated it at the surface you are using .8cf of air. Now you meander down to 100ft and you still need all of that lift so your .8 now becomes .2. You are at 4ata so 4*.6=2.4 for a total of 3.2cf used. You use another 2cf of air because you have a somewhat sawtooth profile, and then you fail to dump properly and have to mostly fill the wing at the surface, for a total of 6cf used for inflation. 6cf is about 250psi out of an AL80 for your inflation gas, really not all that much to worry about. This is really a worst case scenario because you would never really use that much gas on a 100ft dive.

We can talk about some of this in person if you want when you peruse thru some of the gear I'll show you.

 

[Dive Right In Scuba 2]

unless you use the weird UTD Z-system which is an equipment solution to a skills problem. Inflating BC's doesn't take all that much air.
Let's think about it this way.
1cf of water weighs 63/64lbs.

We'll look at worst case scenario, so say you're using one of the big wings, so the Nomad XT with 50lbs of lift. You should be orally inflating at the surface, but even if you power inflated it at the surface you are using .8cf of air. Now you meander down to 100ft and you still need all of that lift so your .8 now becomes .2. You are at 4ata so 4*.6=2.4 for a total of 3.2cf used. You use another 2cf of air because you have a somewhat sawtooth profile, and then you fail to dump properly and have to mostly fill the wing at the surface, for a total of 6cf used for inflation. 6cf is about 250psi out of an AL80 for your inflation gas, really not all that much to worry about. This is really a worst case scenario because you would never really use that much gas on a 100ft dive.

We can talk about some of this in person if you want when you peruse thru some of the gear I'll show you.

This explanation is awesome! Of course most side mount divers never use more than a few "puffs" of gas for inflation. I further reduce that by orally inflating in the event I need floatation on the surface, and occasionally orally inflating during the dive to adjust buoyancy. It's just part of my regular skill routine.

 

[Bubble_blower87]

This explanation is awesome! Of course most side mount divers never use more than a few "puffs" of gas for inflation. I further reduce that by orally inflating in the event I need floatation on the surface, and occasionally orally inflating during the dive to adjust buoyancy. It's just part of my regular skill routine.

Tbone has been awesome offering to show me stuff and help me in a few different ways. It's pretty nice to have people around that enjoy helping others. With the many options and configurations out there, it can really be confusing to a newb. I ask a lot of questions but only because I want to learn!

 

[DA Aquamaster]

I assume from your question that you're new to Sidemount... or just enquiring without any experience in it as yet?

Your cylinders should never run out...... when sidemounting, the diver does not breath one cylinder to empty then start on the other.... the 2nd stage regulators are swapped throughout the dive such that the gas is used across both cylinders and they are kept at very similar levels at all points throughout the dive.....

I hope this helps you to understand?

Most SM divers set up their regulators so that there is an inflator hose on each regulator that is long enough to reach both the BC inflator and the dry suit inflator, so that if you lose all the gas in either tank (blown burst disc or extruded neck o-ring) you can still use the other tank to run the DS and/or the BC.

In the event of a regulator free flow, you have ready access to the tank valve, so you can feather the valve to still breathe off the regulator and maximize the gas in the tank - something that generally isn't an option in back mount.

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However, I'll suggest a minor revision to the bold portion of the statement above.

We've been doing side mount cave dives for about 5 years now, and whether we're using steel 72s, AL72s, AL80s, X7-100s or LP95s, we normally make only two reg switches per dive, and that should be the norm.

For example, with 3600 psi per side with cave filled 95s, I'll start on the left tank and breathe it down to 2400 psi, then switch to the right tank and breathe it down to 2400 psi, turn the dive and begin my exit, but stay on that tank and breathe it down to 1200 psi, before switching back to the left tank and breathing it down to 1200 psi, at which point I'm exiting the cave or on a deco gas.

If I have a catastrophic gas loss just prior to the first gas switch, I've only used 1200 psi from one tank and have 2400 psi left in it and 3600 psi in the other tank. Losing all the gas in either one still leaves me very fat on gas.

At maximum penetration (2400 psi left in each tank), I've used a total of 2400 psi to reach maximum penetration (1200 psi from each tank), and I've still got 2400 psi left in each tank, so I've still got the gas required to exit in either tank in the event I suddenly all the gas in the other one.

If I suffer a catastrophic gas loss just prior to the second gas switch, I've got 2400 psi in one side and 1200 psi in the other, but I'm now only 1200 psi from the exit, so a complete loss of the 2400 psi tank, still leaves me with an adequate reserve to exit.

In practice I've been getting 3800-3900 psi per side on my N-FL cave fills the last few years. However I still us a 1200 psi third and turn at 2600 psi per side. That leaves a 200-300 psi pad in each tank at the most critical points in the dive.

That strategy also ensures that there is no more than a maximum 1200 psi differential between tanks, and even in a large tank like an LP 95, that's a maximum weight/buoyancy differential of only 3.2 pounds. Most side mount rigs will accommodate that with no problem. In an AL 80 and with 1000 psi thirds, the maximum weight differential is only 1.9 pounds.

Many side mount divers seem to make a few more gas switches per dive, but in the vast majority of cases, they are just creating extra work for themselves.

Occasionally, if I turned a dive prior to thirds and I'm consequently coming out fat on gas on one side, I'll make the second gas switch sooner in order to end with both tanks at similar pressures. If I'm filling from different shops with 30% and 32% the even pressures help keep the mix the same in each tanks - but it's still only 2 gas switches per dive.

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Where it can get a little more complicated is with a stage. Let's assume I'm in MX with AL 80 side mount tanks and an AL 80 stage. In this case the 1/3rd available for penetration is 3000 psi total, or 77 cu ft (equal to one AL 80). I'll drop the stage going in at half plus 200 psi (1700 psi left in the tank) with 1300 psi used for penetration, and 1300 psi on tap for exit. I'll then switch to the right tank and dive it to 2,150 psi, switch to the left tank and dive it to 2,150 psi, at which point I've used a total of 3000 psi for penetration, turn the dive, stay on the right tank to 1300 psi, then switch back to the left tank and be back at the stage at about 1300 psi, and then switch to the stage, to exit the cave using 1300 psi from it, leaving 2600 psi total in reserve in my side mount tanks plus 400 psi in reserve in my stage at the end of the dive for a total reserve of 3000 psi. If the stage is gone or empty (1700 psi total and 1300 psi of planned exit gas lost to me), I've still got 2600 psi total left in my side mount tanks to get me out - split evenly between both tanks so that either one is enough to get me out independent of the other one in the event that I lose the gas in a second tank as well.

That increases the total gas switches to 4 per dive.

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As an aside, some side mount divers probably don't bother with the math, and run it a little thinner on the reserve by not factoring in the added gas to increase the 1/3rd reserve, using 1/2 plus 200 in the stage, and then still turning the dive at 2000 psi in the side mount tanks, using another 300 psi total for penetration. In that case, they'll arrive back at the stage with 1000 psi per side. If the stage is gone or empty (1700 psi total and 1300 psi of planned exit gas lost), they've still got 2000 psi total left in their side mount tanks to get them out the same distance it took them 1300 psi to cover on the way in hauling a stage.

It's not the worst plan in the world in side mount as you're still covered for exit gas, where you may or may not be in back mounted doubles. However, it's still busting thirds, and thirds is about more than just gas loss, it's also about having the extra gas and time to deal with unanticipated delays during the exit. To me, the tradeoffs are just not worth an extra 10% in penetration gas.

 

[Subcooled]

what happens when one tank runs out? Obviously you could manually do it but is that the only option?

No, it does not run out.

If it does, buoyancy (should be neutral) is hopefully a minor concern.