question on Doubles manifold isolator

[Lorenzoid]

Since this is the Basic forum, I'll ask a basic question: Isn't the pressure on both sides of the isolator equal (assuming the isolator is open)? If the pressure on both sides is equal, why should it be harder to swing the knob around when the pressure is higher than if the pressure is lower?

 

[Compressor]

You are getting good advice here. The manifold has 2 o rings. That's is what keeps it from leaking not the knobs on the manifold. (AFAIK).
The manifold should not be terribly hard to move under pressure (AFAIK).

 

[Scuba J7]

Since this is the Basic forum, I'll ask a basic question: Isn't the pressure on both sides of the isolator equal (assuming the isolator is open)? If the pressure on both sides is equal, why should it be harder to swing the knob around when the pressure is higher than if the pressure is lower?

If you’re talking just internally, the pressure on the outside of the isolater vs the inside is different and therefore the pressure on each side of the o-rings is different. Some o-rings are designed and lubed to move while under pressure, I’m not sure that isolater o-rings are. If they aren’t then they may twist or tear when moved under pressure.

 

[PfcAJ]

It’s fine.

Get the isolator where you want it and tighten down the locking nuts.

 

[rjack321]

Since this is the Basic forum, I'll ask a basic question: Isn't the pressure on both sides of the isolator equal (assuming the isolator is open)? If the pressure on both sides is equal, why should it be harder to swing the knob around when the pressure is higher than if the pressure is lower?

good question The reality is that
The bands were tight when the tanks were empty but the tanks swell under pressure
Which changes the precise orientation of the bands and makes them even tighter
And despite the manifold being fine thread, puts some minor stresses on it
And its slightly harder to move since one direction is trying to force the tanks apart and the other direction is pulling them together

The manifold orings should be lubricated as they are dynamic orings, not static. You want to be able to tweak the isolator knob by 15degs this way or that. Moving it 90+degs means your bands are either way too loose or the bands are way cheap

 

[Landlocked123]

rjack I believe this is exactly what happened. So my question is what is the correct SOP to setting this up correctly then? if the tanks once filled cause things to bind up some then should one loosen the bands slightly back up after filled and go through the process of re tightening them and re- adjusting the manifold accordinlgy?

 

[Lorenzoid]

rjack I believe this is exactly what happened. So my question is what is the correct SOP to setting this up correctly then? if the tanks once filled cause things to bind up some then should one loosen the bands slightly back up after filled and go through the process of re tightening them and re- adjusting the manifold accordinlgy?

I am guessing virtually nobody does that, but if you did, then you might have the opposite effect: The isolator knob position would become harder to adjust as the tanks emptied. From what rjack says, it sounds like if the o-rings were properly lubed, then making a small adjustment while the tanks are full should be do-able.

 

[sea_ledford]

Since this is the Basic forum, I'll ask a basic question: Isn't the pressure on both sides of the isolator equal (assuming the isolator is open)? If the pressure on both sides is equal, why should it be harder to swing the knob around when the pressure is higher than if the pressure is lower?

The pressure on both sides of the isolator o-rings are not equal. You have double o-rings on each end of the isolator, so prior to filling the tanks you have:
Tank side - Ambient pressure - O-ring- ambient pressure - O-ring- ambient pressure - isolator side

After filling you have:
tank pressure - O-ring- ambient pressure- O-ring - tank pressure

And you have that on both sides of the isolator.

Now there is a very small amount of ambient air between those o-rings, and I imagine they they eventually leak enough to equalize, but that is just a guess on my part. I've often wondered if having a double o-ring in that spot is actually a good idea or not. Isolators seem to introduce a whole lot of failure points to solve one very uncommon one (failed tank neck o-ring). The more I think about it, the more I like independent tanks.

-Chris

 

[Lorenzoid]

That's a persuasive explanation, @sea_ledford. I also found @rjack321 's explanation persuasive that the swelling of the tanks throws things off-kilter.

 

[rhwestfall]

.....and there are so many manifold failures happening......