Doubles question

[cummings66]

OK, I've done a lot of reading on doubles and have a question I've never seen posted. I have read that the isolator knob can rotate for example if you contact a cave obstruction and thus some people prefer brand x over brand y because of how it's put together with double O rings for example.

What I'm wonder is this, how can it rotate? I know without air they can if the lock nut is loose, but wouldn't it be like a regulator where you need to remove the pressure of it's locked solid? In other words wouldn't the pressure in the tanks keep the isolator from being able to rotate?

If it did rotate wouldn't there be an excellent chance of an O ring being damaged and leaking?

[mm_dm]

The pressure in the tanks doesn't keep the knob on the isolator or right hand/letf hand posts from turning. There are drills where you practice turning off knobs and isolating parts of your system in the event of a regulator or tank problem. The double o-rings are for redundancy in the event of a o-ring failure in the manifold set. The problem with one of the knobs turning off is on the left post (your left with the tanks on your back). Since you turn the knob to it's right to shut it off, the knob on your left would turn away from your body to turn off. In a overhead environment like a cave this could happen as you move forward with the knob rubbing against the ceiling of the cave and you would lose use of the items working off your left post (usually SPG, dry suit hose, back up reg) until you manually turned it back on.

[JahJahwarrior]

The actual isolator crossbar on my set of doubles is tight and can't rotate easily. But, the guy who set them up mentioned that some people like them looser....

as far as posts, the left post is the one that could roll off, to roll off your right post you'd have to be swimming backwards....So longhose and inflator go on the right, backup and SPG go on left. If you roll off a post, you don't kill your OOA buddy...the isolator knob couldn't roll off that easily. You'd have to be helicopterin a circle....and on my rig, the thing is angled down, towards my head, somewhat, so I'd also have to remove my head for the ceiling to make contact with it and turn it off.

[ianr33]

The isolator bar (including the isolator knob) will rotate if the locknuts are not tight. Sometime rotates fairly easily,sometimes needs a firm push depending on how clean/lubricated the O rings are. The pressure does not stop it from moving as the sealing O rings are not being pushed flat by the pressure,the isolator rod/tube goes through the O rings. (At least it does on my manifold,I believe OMS manifolds may be different?? )

Some people prefer not to tightem the locknuts so that the isolator will rotate if it hits an overhead rather than shear off the knob.
That may work and I used to do that but decided that it was better to keep the locknuts tight to stop the isolator from moving when transporting tanks.Constant moving when banging around in the back of a truck would seem to be a good way to make the O rings leak.

[cummings66]

Originally Posted by mm_dm

In a overhead environment like a cave this could happen as you move forward with the knob rubbing against the ceiling of the cave and you would lose use of the items working off your left post (usually SPG, dry suit hose, back up reg) until you manually turned it back on.

I wasn't referring to the rolloff, more the actual isolator itself rotating, ie you hit the obstruction and the isolator moves so that the knob is say down instead of up.

[cummings66]

Originally Posted by ianr33

The isolator bar (including the isolator knob) will rotate if the locknuts are not tight. Sometime rotates fairly easily,sometimes needs a firm push depending on how clean/lubricated the O rings are.

Thanks, your post was the one I was looking for as it answered my questions, and even included more details than I was asking. I hadn't heard of people leaving it loose on purpose, but it sounds like it should rotate freely then when the locknuts are loose.

I'm aware of the rolloff issues and valve drills, it'll be interesting to see how it works in the water, but setting with it on my back I can reach them and do it, in the water I will soon find out.

Not that I'm going to get into cave diving soon, but I was curious about the rotation as I'd heard it was possible.

Again, thanks.

[in_cavediver]

Originally Posted by cummings66

I wasn't referring to the rolloff, more the actual isolator itself rotating, ie you hit the obstruction and the isolator moves so that the knob is say down instead of up.

Basically, on my manifolds, 1 halcyon, 2 dive rites and a sea elite, I can rotate the isolator with or without pressure. The o-rings (2 per side) maintain the seal and the threading is there to positition/support the o-ring and set the post separation distance. I tend to keep my locknuts finger tight which does a good job in keeping the isolator where I want it. It does have some give as it has taken a few blows from dropped objects on the surface and no damage.

Its a whole lots of nothing to worry about. Simply set the post distance, set the isolator angle and tighten the locknuts either by hand or with a wrench. Thier tightness won't impact your safety.

[cummings66]

Thanks, I knew you should be able to rotate it empty, in fact the highland instructions tell you that if you can't, adjust it until you can. They made it sound like if you can't rotate half a turn you can damage the isolator/valve, not sure if that's true or not. Mine can rotate empty because they said it should and I made it do so. I'd read somewhere on another board where a user preferred the Dive Rite manifold because if it rotated it wouldn't leak and he thought some others might.

Mine are Genesis, but appear to have the same safety features so I'd say it's not an issue on mine either. Thanks for the confirmation that they can rotate under pressure and it's a non issue.

[texdiveguy]

I use Dive Rite and keep the lock nuts tight to prevent rotation of the isolator bar/knob. In the event of contact with say a piece of wreck structure/rock or even line entanglement I don't want the knob rotating back out of reach...my knobs are rubber and can take a pretty good hit. Its a personal preference.

OP--- so you just getting into doubles diving??

[cummings66]

Yes, I've got some buddies who have been using them for quite some time and I finally decided that due to some of the dives I want to do and the training I want to accomplish this year in order to do those dives, that I might as well start. I've got the gear so I might as well learn to use it.

Both of them are DM's as well and are willing to lend a hand where needed so it helps out.