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Regulator question : Poseidon... worth it?

Cantclimbtom

Well-known member
Apologies for a barrage of questions, just ignore me if this is too irritating. And yes understood opinions/preferences will differ...

But I notice in so many photos of current diving overhead, the second stages are Poseidon (mainly Cyklon 5000?). But the price is at a premium.

As an fairly inexperienced *non overhead* diver who just hires kit and shoves whatever brand in my mouth without noticing that much difference (but aspires maybe one day to do more "interesting" dives), I can't fail to note how popular Cyklon 2nd stages seems to be, at least in the people getting photographed anyway for overhead stuff in UK. They seem to cost a hefty premium. So..
  1. Are they really that good???
  2. Does it make any sense to consider one as a first regulator to buy (future proof) or is this reserved for only when more experienced
  3. Does the resale value mean they work out better value over the long term than any old cheaper regs
  4. Is buying second hand and getting serviced a good idea or is that just foolish
  5. Is it a "marmite" thing and people trained on them just stick to them and dislike non Poseidon
  6. Do people mix and match the first stages, or is it assumed people use XStream as first for a Cyklon second - is there a "best" combination (like XStream not classic, or vice versa)
 

Steve Clark

Well-known member
Can’t really comment on Poseidon because I’ve never dived a set, but they do seem to have a strong following for uk cave divers. They suit side mount being left/right reversible in the water and are small, neat and robust.

If you’re considering general regs for o/w diving, with a view to one day moving to overhead, I’d just buy a set of ‘bottom of the range’ Apeks regs. DS4+ATX40 / XTX40 (the xtx is left-right reversible for side mount). All the other more expensive apeks models are functionally identical internally and just have tweaks with heat exchanger fins and fine adjustment knobs. Also avoid any premium ‘nitrox’/ green / M26 nonsense. Obviously buy DIN.

I’ve used the same model for 20+years and have 8 sets. Bought when they are £125 a set. No issues with any of them at any temperature or depth. They are easy to adjust and service. All uk dive shops that can service stuff will do apeks.

Some other folks in our team of divers use scuba pro mk19 or 25s. They’re slightly more expensive, but lighter for travel and have more options for servicing internationally.

Diving is expensive. Basic, good regs are absolutely fine. You and your friends may find yourself buying lots of sets and it’s simpler for maintenance and projects if they’re all the same.

I wouldn’t normally buy second hand. Most uk regs will have been in the sea, then spent ages in a shed and will need servicing. 2nd hand price + a service is more than the cost of new for basic models.

Poseidon bought from a cave diver may be an exception to that because they’re more likely to have taken a bit of care of them.
 

Pitlamp

Well-known member
I'd agree with much of Steve's post above. Simple is probably best.

Distinguish between "reversible in the water" (i.e. non handed) and "reversible in the workshop" (i.e. left and right handed second stage options which require tools to change from one to the other). The former is much more versatile whilst diving (for example on a stage cylinder).

Steve's point about sticking with one type, so only one type of spares is needed, is a valuable one. Worth also looking into ease of spares availability before investing (Poseidon are notoriously difficult to obtain unless fitted expensively by a shop).

If you're likely to be cave diving rather than just cave diving then the physical size and weight become important factors. Among my own collection are some of the very early (>40 years) Cyclon 300s, which haven't been made for a very long time. They're tiny and will pack into very small containers for cave transport without excessive bending / straining of hoses. They've served me well for all of that time (other than for very deep cave diving, for which I prefer other models). They have thread compatibility issues with stuff currently available but there are ways around this; just saying in case you decide to buy one, which will be second hand by definition.

Whatever type you go for, consider learning (properly) how to service your own. You'll save a fortune, you can then fix problems in remote places (expedition, down a deep pothole, etc) and no-one has as vested an interest as you in getting it right.
 

Steve Clark

Well-known member
“Non-handed” were the words I was looking for! Thanks.

If you do buy secondhand apeks, there was a short period around 2005 where the DIN hand wheel was plastic. The rubber falls off and they cut your hands. It’s a replaceable part but it’s more cost so avoid those. Pic below.

Whether you choose to service your own or use a shop, it’s good redundancy practice to stagger the servicing. You want to avoid the same potential fault (parts, assembly procedure, testing) affecting both sides of your setup on a dive. We’ve actually had this occur with a batch of new regs where they all started gently free flowing after a few hours of use. As above, knowing how to adjust and fix this in the field can save a dive that’s taken a lot of effort to organise.
 

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mrodoc

Well-known member
Well I have a Poseidon that's fifty years old and still works although I am not using it. It belonged to my father. Interestingly one I bought 30 or so years ago wore out and had to be junked. The older models were popular as they could be stripped down easily (second stage). One issue that caused problems was grit getting in the diaphragm causing water ingress with inhaled air! I have had to leave the water sea diving to get grit out but avoided it in caves by a piece of stocking over the mouthpiece. Somewhere in the CDG Journals you will find a reference to a cool headed diver stripping down his second stage for that reason while he was underwater on a very lengthy dive. One reason you dive with two sets of equipment in a cave! Finally first stage adjustment was always an issue depending on who serviced your valve. One chap also returned a valve that would tend to free flow - I think on the basis it gave an easy breathe.
 

JAA

Active member
I’ve not used it but a popular combo with the cool kids seems to be Poseidon 2nd stages paired with Apeks 1st stages. They don’t need a lot of tweaking with the interstage pressure I’m told and parts for Apeks are easier to get hold of.
That said spares are available for Poseidon’s from abroad via eBay and there’s not a great deal to the 300 1st stages although the 5000’s explode into more bits and are fiddlier to do.
 

cap n chris

Well-known member
Vaguely recall reading that Poseidons were preferred to other makes on the basis that in the cold(er) waters in UK cave diving they were less prone to random free-flowing events.
 

Steve Clark

Well-known member
Mixing 1st and 2nd stages does need a little bit of thought. Apeks are downstream valves and will free flow through the 2nd stage seat if the IP creeps or there’s are 1st stage failure / freeze-up of some kind, rather than burst the hose.

I'm not 100% sure on the model names so please do check this, but pairing Apeks 1st stages with the Cyclon downstream style 2nd stage valves sounds logical. The cyclon is designed to work with an IP of 11.5bar, whilst apeks is 9.5bar out of the box, but that can be adjusted. Overpressure would be handled in the 2nd stage.

As I understand it, the newer Jetstream & Xstream regs are upstream design. 8.5bar IP. They have an overpressure valve built into the first stage that deals with any 1st stage faults. If you pair one of those Poseidon 2nd stages with an Apeks 1st stage, you have no effective over-pressure solution and can risk bursting the hose if the IP creeps**. From what I've read, there is something that may/will(?) fail in the 2nd stage first but I'm not sure if this is terminal or not. Consult a reg nerd if you want to have a go at these combos. You can get screw in OPV's to put in the 1st stage but that's another thing to break or catch on stuff.

(**Apeks 1st stages can and do have IP creep if you make an error re-assembling the seat. A thin metal edge cuts a fresh circle in the rubber seat when it's first pressurised and adjusted. If you subsequently disassemble it and put it back together without replacing with a new rubber seat you can get two slightly offset circles that don't seal properly and slowly leak, causing the IP to rise over time if the reg is pressurised but not regularly breathed off. )

From the factory / shop service tech, Apeks are set close to free-flow. If you purge a reg with the mouthpiece pointing upwards it will set off a continuous free-flow. Somewhat mis-guided fine tuning to get the easiest breath etc. as noted above. This probably explains the reputation for free-flows. That's not always ideal for cave diving and I de-tune my backup regulator 2nd stage that lives around my neck to stop it free-flowing in the scooter wake.
 

PeteHall

Moderator
One of the great benefit of the Poseidon Cyklon 2nd stages is the ability to strip and clean the grit out of them in a cave, even underwater if necessary. I think this is the main reason they are favoured by British cave divers.

Price really shouldn't be a problem, Keeping an eye out for 2nd hand, I've picked up a complete metal bodied Cyklon for £5! Admittedly, you'd normally expect to pay 10 to 20 times that price. Service parts aren't too cheap, but they can be tuned at home to keep them in good working order without the need for regular replacement of parts.

I’ve not used it but a popular combo with the cool kids seems to be Poseidon 2nd stages paired with Apeks 1st stages. They don’t need a lot of tweaking with the interstage pressure I’m told and parts for Apeks are easier to get hold of.
Apeks DS4 1st stages run at a lower inter-stage pressure than a Poseidon 2st stage, so technically speaking, you need to tune it up a bit. In reality, the Cyklons perform fine connected straight onto an Apeks DS4 without any tinkering. A a smoker once described it to me "you have to toke them a bit", but I've never found this to be a problem.

The Apeks 1st stages need servicing less frequently and service parts are cheaper, they are also a robust regulator that performs well in UK sump conditions. They can usually be picked up 2nd hand for £50-£100

This obviously assumes that you're happy to ignore manufacturer recommendations and accept liability for your own actions!

As @Pitlamp says, some of the Posedon 1st stages are really small and light and I have one set that I keep for this reason, but for almost everything, I use DS4's with metal body Cyklon's, despite the slight extra weight.

I am told that other 2nd stage regs breathe nicer, but since I've never used anything else, I have no other benchmark and I've never had an issue using Cyklon's.
 

Cantclimbtom

Well-known member
Mixing 1st and 2nd stages does need a little bit of thought. Apeks are downstream valves and will free flow through the 2nd stage seat if the IP creeps or there’s are 1st stage failure / freeze-up of some kind, rather than burst the hose.

I'm not 100% sure on the model names so please do check this, but pairing Apeks 1st stages with the Cyclon downstream style 2nd stage valves sounds logical. The cyclon is designed to work with an IP of 11.5bar, whilst apeks is 9.5bar out of the box, but that can be adjusted. Overpressure would be handled in the 2nd stage.

As I understand it, the newer Jetstream & Xstream regs are upstream design. 8.5bar IP. They have an overpressure valve built into the first stage that deals with any 1st stage faults. If you pair one of those Poseidon 2nd stages with an Apeks 1st stage, you have no effective over-pressure solution and can risk bursting the hose if the IP creeps**. From what I've read, there is something that may/will(?) fail in the 2nd stage first but I'm not sure if this is terminal or not. Consult a reg nerd if you want to have a go at these combos. You can get screw in OPV's to put in the 1st stage but that's another thing to break or catch on stuff.

(**Apeks 1st stages can and do have IP creep if you make an error re-assembling the seat. A thin metal edge cuts a fresh circle in the rubber seat when it's first pressurised and adjusted. If you subsequently disassemble it and put it back together without replacing with a new rubber seat you can get two slightly offset circles that don't seal properly and slowly leak, causing the IP to rise over time if the reg is pressurised but not regularly breathed off. )

From the factory / shop service tech, Apeks are set close to free-flow. If you purge a reg with the mouthpiece pointing upwards it will set off a continuous free-flow. Somewhat mis-guided fine tuning to get the easiest breath etc. as noted above. This probably explains the reputation for free-flows. That's not always ideal for cave diving and I de-tune my backup regulator 2nd stage that lives around my neck to stop it free-flowing in the scooter wake.
Aahhh.. a couple of months ago hired apeks (because that's what they had) and on connecting it up had a small leak from the overpressure port on first stage and I went back and swapped it for another. They shrugged and said they'd put in the pile for service and didn't raise any eyebrows. But I wondered what sort of fault might cause over pressure of IP that seemed so mundane to them, perhaps it was this? (I assume the first stage was Apeks because the second and octopus were).

And thanks for such a detailed tutorial above.

I'm really getting schooled from all these helpful posts in the thread all are appreciated thanks!
 

Steve Clark

Well-known member
There is no over-pressure port on an apeks first stage. Possibly my confusing explanation above? In the event of IP over-pressure it will force open the valve seat in the second stage and free-flow a bit depending on how bad it is. Hence you shouldn't use a different brand 2nd stage that won't do this by default.

If it was leaking out of an Apeks first stage itself, it's likely one of the o-rings has gone dry or crusted up a bit. If it's around one of the ports or DIN then it's easy enough to fix by taking a hose off or reseating the DIN. When it leaks out the side of the body, it's passing where the diaphragm is clamped and it's time for a service.

This is quite a good explanation animation as to how a balanced diaphragm first-stage works (from wikipedia.) This is almost identical to an apeks 1st stage cross section. In simple terms, the valve's main job is to take whatever input pressure from the cylinder, compare it with the water pressure and open just enough to deliver a consistent +9.5bar above the ambient water pressure then shut. The second stage deals with 9.5bar down to ambient. (There is a further refinement of being 'over-balanced' where this actually increases a bit more than 9.5bar above ambient at greater depths to compensate for increase gas density and viscosity.)

The purple bits are all the o-ring seals where it can leak.


The other important job of the first stage is thermal. When the gas expands from (say) 200bar to 10bar it cools dramatically. Like spraying a can of deodorant. If there is any water in the gas this can freeze up in the valve. Hence compressors have drying filters. On all the sealed apeks first stages (not the US4), there is additional diaphragm at the bottom that stops any water getting in around the springs, whilst still transmitting the water pressure to the valve mechanism. This is the clear squishy membrane you can see on the end of the reg. Hence "dry sealed" & "suitable for cold water" you will see in the marketing.
 

Cantclimbtom

Well-known member
Been quiet on the thread as gone down a bit of a rabbit hole for a while in things related to valves/regulators/gasses/servicing costs/etc. (unfortunately despite having a mechanical turn of mind, not sure self servicing is wise unless I get training or a lot more experience or both)

I think I need to back off, get more knowledge and experience, then return here for another good read!

Thanks again everyone!
 

Cantclimbtom

Well-known member
.... A a smoker once described it to me "you have to toke them a bit", but I've never found this to be a problem..
Actually for me that sounds an advantage. Probably to bemusement and horror of "real" divers I'm not at all a natural diver. Intuitively I do the opposite of good diving :( For example: left to my own devices I will trickle air up my nose a little as I breath in and a little out as I breath out. Not at all helpful. To mitigate those poor soft palate habits I have to imagine breathing out with a little force/tension like blowing up a balloon (or I fog my mask) and on the in breath I imagine sucking a very thick milkshake. I have to remind myself the cues if I haven't dived for even a short while. A reg that I have to toke a bit would be a distinct plus for me! :(
 

Cantclimbtom

Well-known member
Thanks again everyone, there's a wealth of info and experience above!! Greatly appreciated!

Even though I'm not certain that Poseidon (e.g. Cyklon 5000) is doable due to cost... although the consensus here seems to be they're worth it.

Apeks DS4 sounds an all round good first-buy for a first-stage, that can be paired with Cyklon 2nd if toking it isn't seen as a problem, or an Apeks workshop reversible 2nd, so DS4 sounds a good choice.

If someone has limited equipment and wanted to use a DS4 first with a Cyklon??? 2nd, noting the inter stage pressure is a little on the low side for the Poseidon, and got a bog standard Apeks octopus for use in back mount recreational settings, would I be right that it may look unorthodox, but be an acceptable combination... any gotchas I've missed there?
 

Steve Clark

Well-known member
I think you’ll probably get a better deal buying a set of ds4+black xtx40 + yellow xtx40 in one go. As individual parts a ds4 + yellow xtx40 will cost about the same.

If I was putting (just) a cyklon on a ds4 I’d adjust the IP. Mixing two different spec IP 2nd stages on the same first stage IP isn’t a great idea because one of them isn’t working as designed.

If you like the idea of having some effort to breathe, you can just adjust an apex’s 2nd stage to do that. There’s two parts to this :

The Venturi adjustment (+/- lever on the side) adjusts how easily the gas is delivered once the breath has started. This is available on xtx40 & xtx50 as standard. You can adjust this mid-dive for comfort. Typically I’d have the primary reg set to +, the backup set to - to reduce the chance of free flow.

The cracking pressure adjustment controls the initial pressure you need to ‘suck’ to start the gas flowing at the start of a breath. On an xtx50 this is adjusted by a knob on the opposite side to the hose and can be done mid-dive. On an xtx40 you can do it with an Allen key in the same spot. (You can also buy an eBay part to make an xtx40 into an xtx50).

If the ‘feel’ of the breath is important to you, a set of ds4+xtx50 black+xtx40 yellow is a solid start.

There’s also the DST, which is a ds4 with a swivel turret (-T). Some folks prefer these for using for side mount later. I’ve not no practical experience of side mount and a CDGer would know best if this is worth bothering with. I’ve got one on some stage regs and it’s not much better, just heavier.
 

Steve Clark

Well-known member
I’ve just googled for some deals and genuinely shocked at the current pricing. Generally double the price they were on offer for in 2020. I fear for university dive clubs and the like.

I’ve bought a lot from these guys in the past. There’s a decent deal here on ATX, as cheap as 2nd hand eBay+ a service but they’re not reversible so not ideal for future sidemount use. You want xtx really.

 

PeteHall

Moderator
There’s also the DST, which is a ds4 with a swivel turret (-T). Some folks prefer these for using for side mount later. I’ve not no practical experience of side mount and a CDGer would know best if this is worth bothering with.
The general concensus, speaking to various CDG divers is that the DST is just more to go wrong. It's quite easy to set up your hoses in a comfortable way for either side without the swivel, so why add the extra weight and extra mode if failure?

I'll caveat that by saying that no two CDG divers configure their kit in exactly the same way, so obviously opinions do vary, but  most people agree on the above in the context of Apeks 1st stages.
 

Cantclimbtom

Well-known member
Thanks DST seems a fair bit more expensive too. I can't see myself needing 2 HP ports either (SPG and computer sender?) . The DS4 looks simple and decent price
 

Pitlamp

Well-known member
Don't forget though that more ports means more possible hose orientations, so you have more options to fine tune hose routing.

I'm not a fan of those devices that rely on a magic beam to display the cylinder pressure. I can envisage some advantages but there's more to go wrong.
 
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