Sidemount or Backmount?

[Vegan Shark]

When you BM independent doubles, and switch regs every 500 psi or so like SM, is there gas loss from the tanks when they're not being used? I'm not clear on if SM divers turn off a tank when it's not being used, then re-open when they switch, or if both tanks are just left open the duration of the dive.

Is the only advantage of a manifold the fact that you don't have to bother with switching regs unless there's a failure?

 

[ajtoady]

Every gear configuration has it's own pros and cons. The amount of air I loose in a reg switch is minute and as far as switching off a tank and shutting it down, it don't happen unless there is a problem. I have invested in quality gear and I maintain and test it frequently. Regardless of the configuration, if I am wearing a tank in back-mount twins, side-mount twins, or BM single with a pony, the tank is always turned on and ready for whatever may happen. The safety of the two tanks lies in the fact that the possibility of two total failures is remote due to two entirely independent 1st and 2nd stages. As a side note, I wear my pony (30 cu ft) side slung any time I go beyond 60' in a normal single primary BM tank dive. I may be a little over cautious but, it's my choice. I like to breathe when I dive.

 

[rivers]

In manifolded twins, in the event of a first or second stage failure, you still have access to all of your remaining gas. The dive is over as you no longer have a second reg to assist your team however. But, if you're in a wreck or cave, or have a considerable deco obligation, at least you have access to all remaining gas.

 

[PfcAJ]

In manifolded twins, in the event of a first or second stage failure, you still have access to all of your remaining gas. The dive is over as you no longer have a second reg to assist your team however. But, if you're in a wreck or cave, or have a considerable deco obligation, at least you have access to all remaining gas.

This is a really big deal, too. Often overlooked. Gas loss problems can quickly turn into gas loss + a delay when cave diving. Access to that extra gas can make a huge difference.

 

[Vegan Shark]

Gotcha. So if you're using manifolded twins, and your primary first or second fails, you simply switch to the backup and still have all your remaining gas? No valve drills or anything requires? I thought if one fails you used the isolator to isolate the tanks, and then just used the functioning tank.

Anyone know a very comprehensive online guide to using manifolded doubles, with all the drills, etc.?

 

[PfcAJ]

Negative.

You turn off the valve for the broken regulator. That stops the leak and gives you access to everything you have remaining. The isolator is for 'manifold' failures like the crossbar orings, tank neck orings, burst disks, and the like.

 

[rivers]

Gotcha. So if you're using manifolded twins, and your primary first or second fails, you simply switch to the backup and still have all your remaining gas? No valve drills or anything requires? I thought if one fails you used the isolator to isolate the tanks, and then just used the functioning tank.

Anyone know a very comprehensive online guide to using manifolded doubles, with all the drills, etc.?

If you know what post is having the issue, you close that post. You close your isolator if you're not sure. It could be your right post with your primary first stage. It could be your left post. You want to save as much gas as you possibly can.
And it's called a day of coaching. Many different instructors from many different agencies teach courses, that will teach you how to properly to a valve drill, etc. GUE have a double primer, but also teach the valve drill in fundies and expanding into failures in its tech and cave classes. TDI and IANTD have intro to tech classes. BSAC now have their twinset course. You can do all the reading you want, but either an instructor or an experienced mentor is your best bet on learning the drill properly

 

[nimoh]

Gotcha. So if you're using manifolded twins, and your primary first or second fails, you simply switch to the backup and still have all your remaining gas? No valve drills or anything requires? I thought if one fails you used the isolator to isolate the tanks, and then just used the functioning tank.

Anyone know a very comprehensive online guide to using manifolded doubles, with all the drills, etc.?

not quite.

if your primary reg fails, you would switch to the back up reg and close the tank valve on the side with the failed reg. The manifold will allow the gas from both cylinders to equalize while you are breathing, giving you access to all of your remaining gas.

The manifold valve is used to isolate the tanks when the problem can't be fixed with a tank valve shut down such as a tank o-ring failure, or blown burst disk. Isolating the tanks will prevent the gas from your good tank from flowing out through the failure in the other tank.

 

[TSandM]

Vegan Shark, HERE is a thread about manifold failures. Hopefully, this will help you understand the issues.

 

[Vegan Shark]

Thanks! I plan on beginning tech courses later next year, but have been thinking of switching to BM doubles in the mean time just for the redundancy on solo dives/being able to do one real long dive for the day since once I'm back on land I feel like just heading home instead of going for fills and then jumping back in the water again.

From that thread it sounds like most of the failures would require a buddy to help out, but am I correct in thinking there is no failure that would cause both regs to stop supplying air, so in case of failure during a solo dive I could just switch to backup and call off the dive?