One for the Myth Busters.....

[dan_gadget]

Purely for discourse (I do NOT intend to attempt it)

Why couldn't I join a couple (say 232 bar) of tanks via a high pressure hose, similar to Gauge hose from the first stage high pressure ports?

If I set up one tank standard yoke and the other with a first stage all capped off. Then get a piece of high pressure hose with 3/8ths thread either end join the two first stages how high will I blow myself?

Seriously, I can't see that it wouldn't work in principal (from a technical aspect, I.E. Safety aside!)

Are there any thoughts that aren’t too scathing?

Loads of love,

Bloody stupid Dan.

[ianfirmin]

What could be wrong technically? If you are using components within their design tolerance you'll have no problems. It really depends on what you want to do with it. Do you hope to breathe from one side and have the HP hose equalise the pressures? You then need to consider flow. For instance, gauge hoses have a very small hole to restrict flow. Certain (if not all) primary regulators are not design to provide much flow at all out of the HP port.

Are you banding the cylinders together so the hose is not capable of being over-stressed? You need to tell us want you want this setup to do before any meaningfull comments can be made.

[dan_gadget]

Ok. i wasn't sure it wasn't just a plane dumb question.

We're banding the tanks with a buddy Bcd twinning system. so we'd appreciate the flexibility in any connection.

We're hoping to have one gauge set and have the tanks balance as we breath.

Any other details are negotiable.

Again. This ( if not just plane stoopid) is only hypothetical.

[Graham_Pettett]

A while ago I dived with Mark Andrews (air world depth record holder) and he does exactly this to include a 3rd back cylinder to make a 'tripple set', pretty impressive.

Graham

[Nigel Hewitt]

Why couldn't I join a couple (say 232 bar) of tanks via a high pressure hose, similar to Gauge hose from the first stage high pressure ports?Gauge hose is very small bore so won't equalise but the sort of hose you use for filling tanks would work.

Check the regs for the size of the feed hole into the HP outlet first

The only problem now is that you don't have the crucial trick of the twinset that when you shut one valve you can still breath on the other one so I can't quite see the point. No redundancy so I wouldn't take it into deco as I'm a coward.

[David Walker]

From what I understand, you're talking about effectively making a manifold from a hose between two independent regs / cylinders?

Never thought about it before, but its probably not a bad idea.

If I were to do it, i'd keep a standard manifold twin setup, with regs on each tank - so the hose is only balancing the pressure.

Two options for balancing - HP or LP.

LP may be easier, since it's larger bore and you could put those little Apeks anti-freeflow valves in to maybe even act as a kind of isolating manifold. However, i'm not sure it would work at LP because the reg wouldn't be able to "recompress" that LP back to HP in the other cylinder. But if the pressures were kept the same, maybe that wouldn't be an issue, if the "isolator" is kept open? Might be worth a try anyway. Only potential problem (on the "blowing things up scale") is how a first stage reacts if it gets 10 bar on the downstream part (ie across you "manifold") if there isn't sufficient pressure on the upstream part (ie the cylinder to which it's connected).

HP is therefore the more simple approach, but limited by the small bore of the hose. Don't know what the flow rate is, but it certainly won't be enough to breathe from, so is slightly more limited than a conventional manifold. However, it will easily be enough to keep two decent sized cylinders balanced, at the HP side. However, if it goes then you're totally screwed, losing both cylinders. You could maybe put in some valves to again create a type of isolator valve, if you look at the valves used in filling whips? Might prevent a big problem if the hose goes.

Interesting idea though.

David

[dan_gadget]

Thinking about it further, since you'd be saddelling on after the pillar valves you'd be able to isolate one tank from the other simply but turning it off. no?

In the case of the primary (if you will) turning off would leave the 'secondary' tank feeding the regs through both first stages. turning the 'secondary' tank's valve off would isolate the 'primary' which would simply keep feeding the regs in the normal manner. just with a dead ended hose sticking out the side.

Or have just totally missed the point of isolating?

I should really come clean about now and say that i have absolutely no experience with tech diving. Once i become VERY much more experienced i shall be finding out more, under guidance. Currently however i've only about 15 rec. dives under my weight belt. so i've only just got a toe in the water.........sorry.

Long term, i'd like to be able to go to a dive Outfit with my AP Commando,Redwing and twinning bands and without tools rig up a twin set using their bog standard a yoke cans. These being Aluminium 15L. Weight aspects aside, am i now really talking crap?

[ianfirmin]

Without wishing to start any discussion on the comparative merits of independent twins vs. manifolded twins, why don't you just use them as independents? Two tanks, two sets of regs. No connection between the tanks needed.

A quick look through the archives will give you the pros and cons of such an arrangement however it's a well proven and tested system used by many people (including me). It strikes me as being a better system than using flexible hose with all the additional problems associated with "additional points of failure" "difficulties with providing isolation between the two tanks" blah blah blah.

Cue the indie vs. manifold debate......

[Nigel Hewitt]

Joining two tanks on the LP side does not balance usage.
The first stage with the fractionally higher IP setting will dominate the flow keeping the other one shut off. One tank will empty first then the second will start.

I fall back to my earlier point that joining tanks after the pillar valve removes the point of having two tanks and two regulators. You cannot shut of a free flowing reg (a common enough fault that many of us have seen) and still have something to breath. You are down to one big tank and one reg with a lot of extra clutter to go wrong.

I can't come up with a scenario where running the tanks as independents isn't a simpler, safer technique.

[Charles Stirling]

The HP ports on 1st stage regulators is tiny to seriously limit flow if a pressure gauge or hose blows. Connecting at this point won't balance against breathing usage.

Manifolding valves connect before the regulators and I can't see why a flexible connection couldn't be used at that level, but it might not be as robust as a solid connection. To then use the cylinders independently you would need to have blanking plugs for each valve. Maybe a good way to get sea water into the tanks (as no pressure in them when changing) so destroying them.

Charles

[richc]

The HP ports on 1st stage regulators is tiny to seriously limit flow if a pressure gauge or hose blows. Connecting at this point won't balance against breathing usage.


So you're saying that the gas doesn't flow as fast down an HP hose as I can breathe? Ever had an HP hose go underwater? Or a pressure gauge go? Ever timed how long it takes to empty a tank that way?

I really don't think you are breathing that fast.

I agree that they won't balance on the LP side and drain tanks evenly but I'm not sure it matters - whether you connect LP or HP you're still diving one big tank with one failure point that will lose all the gas. You just might feel a bit lopsided if you linked the LP sides as it will drain one tank first and then teh second depending on the IP settings, but the risks are about the same. In fact there is an advantage in the LP connection in that if you came back with 50% of the gas you'd only pay to fill one cylinder potentially rather than a twinset.....

Rich

[Mike Halligan]

So you're saying that the gas doesn't flow as fast down an HP hose as I can breathe? Ever had an HP hose go underwater? Or a pressure gauge go? Ever timed how long it takes to empty a tank that way?


Nigel and Charles make sense to me. I've had both HP and LP hose failures (in separate incidents). LP is much, much worse. My digital contents guage had difficulty keeping up with the loss when LP went.

HTH
Mike

[David Walker]

Nigel and Charles make sense to me. I've had both HP and LP hose failures (in separate incidents). LP is much, much worse. My digital contents guage had difficulty keeping up with the loss when LP went.

LP is definitely worse, but given that someone might last say an hour on a 12l cylinder, the HP hose going is going to empty the cylinders much much quicker - therefore it has enough flow to balance the pressure. That doesn't mean you could breathe straight through the HP hose, because the flow during an intake of breath is much higher - but to balance the tanks, there's more than enough flow.

David

[Mike Halligan]

LP is definitely worse, but given that someone might last say an hour on a 12l cylinder, the HP hose going is going to empty the cylinders much much quicker - therefore it has enough flow to balance the pressure. That doesn't mean you could breathe straight through the HP hose, because the flow during an intake of breath is much higher - but to balance the tanks, there's more than enough flow.

David

David,

Are you sure the volume of gas actually passing through a ruptured HP hose will exceed that through a ruptured LP one? I'm not convinced. :)

IIRC, my 12 lost 150 bar in around 6 minutes when the LP went, plenty of time for a well-trained DL buddy to take command through a cloud of bubbles and get us both to the surface. :cool:

[David Walker]

Are you sure the volume of gas actually passing through a ruptured HP hose will exceed that through a ruptured LP one? I'm not convinced. :)

Oh, no, I meant LP is worse for losing gas quickly (ie faster flow). But the rest still applies - while HP has lower flow than LP, it would still be far more than required to keep two cylinders balanced as they're breathed down.

David

[johnskerry]

I have often thought that a flexible manifold could be useful in terms of easily altering configurations of cylinders.
Using the HP port would seem to be the best approach as under failure you have a bit more time, however the main problem with twining cylinders in this way is you have effectively created one large cylinder which you cannot isolate ( a choice of free flowing air or no air)
However it might be useful for increasing capacity of twins, i.e. I dive on twin 10 (upside down and manifold), this is usually fine, however occasionally more gas is required. At present I deal with this with a 5 bolted on the side plus reg or side slung plus regs. This can result in lots of regs some with different mixes. If on the other hand I fit say a three on each side connected to the HP ports I can still retain the ability to isolate without an additional reg. Just imagine the dives I could do on Twin 10+5s and two side slung Alu 10s. ?
Still a nagging doubt in my mind though.

[Janos]

So you're saying that the gas doesn't flow as fast down an HP hose as I can breathe? Ever had an HP hose go underwater? Or a pressure gauge go? Ever timed how long it takes to empty a tank that way?

I really don't think you are breathing that fast.

Yes - I've had an HP hose go. (Well my buddy did). We'd just got down to around 35ishm when he had a look at his pressure gauge and it came off in his hand. He went onto my octo and we did a normal ascent, including 3mins at 6m.

By the time we were back on board, and had dekitted him and turned his tank off, he still had over 100 bar left.

HP hoses are very thin.

Janos

[Mike Halligan]

Oh, no, I meant LP is worse for losing gas quickly (ie faster flow). But the rest still applies - while HP has lower flow than LP, it would still be far more than required to keep two cylinders balanced as they're breathed down.

David
Oh, right, most likely would in normal use.

But Nigel was suggesting that the higher IP would hold back the balancing. If he's right, would we reach a position where the HP linkage is doing little more than replenish gas consumed and therefore doesn't provide a margin for hard work, anxiety, buddy use?

[Nigel Hewitt]

Oh, right, most likely would in normal use.

But Nigel was suggesting that the higher IP would hold back the balancing. If he's right, would we reach a position where the HP linkage is doing little more than replenish gas consumed and therefore doesn't provide a margin for hard work, anxiety, buddy use?That was connecting at the LP level where, naturally, which ever reg is set to the fractionaly higher IP will always flow first and keep the other one switched off.

I'm sure with a small pillar drill I could render an HP port high flow and with a fill whip hose make a connection but it still comes comes over as a bad idea because all you are doing is making one big cylinder because shutting off a valve does not leave you access to the gas and, anyway, it does not disconnect the free-flowing reg.

[ianfirmin]

Why does someone not try it? Connect two HP ports together with a high pressure hose and breathe one side down. The flow between the cylinders will be a function of the pressure difference, density of the gas (ok, ok, Reynolds number, fluid viscosity etc..) and the restriction to the flow. The restriction to the flow will be mainly the orifice sizes, at the ends of the HP hose and inside the regulator. The pressure difference will be caused by one side losing pressure.

With a constant loss from one side (steady breathing) the flow rate between the two cylinders will stabilise at a certain pressure difference. If this pressure difference is not too high then it will work. However, gas viscosity increases with pressure, and restriction to flow increases with a higher flow. The pressure difference at 2 atm with one person breathing at a low sac rate may be small and acceptable. With 2 people breathing at high sac rates at 5 atm things will change...

With measurements taken at 1 atm on different rates of flow it will be possible to calculate the flow rate/pressure difference at different depths. Who wants to do it? Any bored Mech Eng students out there?

[NJT]

I considered this some time ago. And was advised against it.......too complex and too many points of failure.

Linking the LP is nonesence.

As Nigel stated. Linking HP via the HP ports is only making one big tank, that in the event of freeflow, hose failure, etc needs an isolating valve otherwise you would be left with nothing to breathe. Ignoring the flow issues for a moment.

A better way would be to have a couple of H valves and a short decanting whip connecting them. but that is an extra valve to shut down in the event of a freeflow. And I am not sure there is enough space to have the valves positioned correctly, the second valves on the H of each tank would interfere with each other.

The cost of new valves and decanting whip was a much as a manifold and bands.

I gave up and bought a second hand set of manifolded 12s. In addition to the 2 12s I had aquired already. I still have the extra twining bands and have turned up at dotty with 2 twin sets before now, one as indies.

I have dived indies a number of times including a single 15 and a 7l stage. You need to think gas management, in this case 1/3s. But we should be doing that anyway.

If anyone has any further thoughts on this system I would be interested.

Regards
Nick

[ianfirmin]

I agree that it would produce one large tank in the same way that a non-valved manifold would do. I can't see how it has more points of failure though.

The only advantage I can see over a rigid non-valved manifold is that it's flexible which could be useful under certain circumstances.

I personally dive with a valved manifold and nice rigid SS bands holding everything together and would not do it any other way. If I had to use two tanks on floppy cam bands I'd dive them as Indies.

No one said it was a GOOD way they just asked if it would work. It may do.

[Ben Panter]

I agree that it would produce one large tank in the same way that a non-valved manifold would do. I can't see how it has more points of failure though.

The only advantage I can see over a rigid non-valved manifold is that it's flexible which could be useful under certain circumstances.

If one reg on an unvalved manifold goes pop, you can turn off that pillar valve and still breathe all the air in both tanks.

If one reg on a HP-port linked set goes pop, even switching off that pillar valve will not stop the regulator free flowing, as it still has an HP source from the other tank. This is what is meant by 'increased failure points'.

That and the fact that it is a cm wide rubber covered wire hose rather than an inch thick chunk of steel.

The only advantage over independents is that both tanks will drop at the same rate. For this tiny benefit (that you don't have to switch regs regularlly) you essentially are diving one big tank with two first stages on it, neither of which can be isolated.

Linking a pair of first stages through their HP ports is not a sensible way to dive, although it *might* allow tanks to equalise.

Ben

[Vic]

I agree that it would produce one large tank in the same way that a non-valved manifold would do.

No, you've missed the point.

If you link your regs via the HP sides, you have created the situation where you cannot stop a failure.

If one reg were to freeflow, shutting down the pillar valve will save the gas in that cylinder - but you cannot get to it. It is completely isolated.

The other cylinder, however, is still connected to the freeflowing regulator.

So you have the choice between isolating your gas (and therefore making it impossible to breathe), or watching it spew out from a failed reg.

The *only* advantage that this HP-linking scenario brings is that, in the event of a neck O-ring failure, isolating that cylinder will allow it to empty without emptying the other one as well. But that moed opf failure is significantly less common than a reg freeflow.

But other than that, this method merely makes you reliant on having *both* of your regulators functional, rather than *either*, as is the case in manifolded or independent twins.

Vic.

[ianfirmin]

Of course, you are right. Engaged keyboard before brain was in gear....