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Poseidon XStream Deep 90

ABOUT POSEIDON
Poseidon was founded by divers, for divers. When Ingvar Elfström launched the worlds first single hose regulator back in 1958 it became an instant sensation. Since then Poseidon engineers have continuously strived to make the best of the best (which is often reflected by the price, but shop around and keep in mind used gear can be as good as new after a service). Used by many military, NASA and other commercial divers all over the world, Poseidon equipment has set many standards.

The Poseidon Xstream is Poseidon's most recent regulator series (following Triton, Cyclon and Jetstream).

Although it was originally launched in 2002, it has gone through several revisions and improvement, both in the first-stage as well as in the second stage design.

It is one of the few so-called "upstream regulators", meaning the second stage needs to be pressurized in order to close. This results in a short burst of air coming out of the second stage when opening the tank valve, something that surprises some divers inexperienced with the unit. Contrary to what you are told during your Open Water course, you should not open the tank valve slowly on an XStream - open it swiftly and hardly any excess air escapes through the second stage, about 3 liters approximately - that's one breath...

The Xstream uses a dual-valve design which allows the XStream to deliver the perfect amount of air, even at greater depths, without any need for a "venturi assist" or other regulation mechanism on the second stage. This simplifies operation for the diver. Due to the compact and streamlined design of the second stage with side-exhaust, this regulator can be coming from the left or right, and even swimming on either side or upside down works perfectly. It is also a great reg for scootering, as the purge button is on the side and protected from accidental purging by the water pressure. As evident by a couple of YouTube videos of some Swedes scootering under a winter lake... ;-)

To purge the XStream, press the side of the second stage, not the front. Due to the very effective (high volume) delivery of air, a fully pressed purge button is one of the most heavily criticized issues with the XStream. However, there are three things to be said about this:

1. The need to purge is virtually non-existent due to the extremely small volume of the second stage. We have found we can easily breath in "over" the water in the second stage even with pretty much empty lungs (if breathing normally, you always have a residual lung colume which you can "force out" as well), simply exhaling will clear the little water in it anyways (just like a snorkel designed to assist drainage).

2. The purge button can be touched lightly for a lighter "swoosh" - something most oversee in their reviews. Pressing it fully - yes, alright, it will deliver around 2,100 liters of air per minute, and you could probably propel a small inflatable with it. It might even work as a deterrent to nosy sea creatures or divers you don't like to have close to you ;-) 

3. The design was actually changed several times - in August 2005, to allow for a new diaphragm cover (article number 4536) to be fitted with the service level 2. This allows a larger area to be pressed, instead of having to use a single finger (some apparently couldn't get theirs in...). See Poseidon press release.

The first stage is a bit of an industrial design marvel. To my knowledge there is no simpler design of a first stage, with so few parts (=less items that could fail!). First of, there is no piston that can become dislodged, misshaped or mis-aligned. Instead, a round stainless steel ball rests on the valve to always operate perfectly. The first stage is not environmentally sealed, but instead uses comparably huge openings to effectively allow water (even when diving in ice cold lakes the water temperature is around 3-6 degrees Celsius) to warm the metal parts of the XStream, preventing any form of ice build-up.

This image shows how simple the design is - the plastic separator disc in the upper third prevents heat (or cold) transmission, there is a stainless steel round ball in the bottom which can not become dislodged or bent like traditional pistons:

This is the most current model of the Poseidon XStream Mk3 (revision of Fall 2008) - the surface finish is now matte instead of chrome (like on the Deep 90) and, more significantly, features a built-in overpressure valve so you can use STANDARD hoses (finally!) - or Miflex hoses:

Note: the red cap is only a protective cap for transport - rightfully assuming you will at least want to plug one IP hose into your regulator, this saves an unnecessary "blind screw". 

The following illustrate the operating mechanisms:

Poseidon Octopus - identical to the "primary second stage", the difference is the color of the rubber cap (user replaceable):

Poseidon first (old design) stage and primary second stage:

Note: The follow-up model (Deep 90) of the XStream first stages came with a metal top for better heat dissemination and a full-body chrome finish. The newest incarnation, the Mk3 has a matte-surface finish (see larger image above with the red protective cap in place) and features an integrated overpressure-valve so any standard hose (including Miflex hoses!) can be used with the XStream set. 

Poseidon used to use special hoses with built-in overpressure valves/vents near the second stage connection (in case the first stage would fail and flow continue to the second stage, remaining breathable. Note regarding some people warning about it "failing shut" instead of "failing open" - I have, despite reading English, German and Swedish dive forums (lots of cold-water diving happening in Germany, Austria, Switzerland and Sweden!), never came across a case of a Poseidon XStream first stage failure under normal dive conditions. The fact of non-standard hoses is also much criticized, however for normal dive operations this was always negligible (just carry a spare!). Poseidon branded hoses also used to be very expensive (three times the price of standard hoses, but they are not really anymore - i.e. a 210cm hose is now in the range of 45 Euros - the same as a Miflex hose, no bid deal (yes, you can probably find a standard hose for as little as $23 somewhere if you must - personally I stick to the superior Miflex variety!). 

In Fall 2008 the XStream got another design and functionality improvement. The new model, named Poseidon XStream MK 3, did not only receive a matte-looking metal case of the first stage, but the key news is the integration of an overpressure valve into the first stage, thereby eliminating the need for a 'special Poseidon hose'. The existing/older second stages can be used with the newer first stages (this basically gives you an extra overpressure valve, no harm there, or use an inexpensive adapter to use your old XStream second stage with a standard hose (or Miflex Xtreme diving hoses). If you are thinking of replacing your hoses, give Miflex hoses a thought, we and many others are very much impressed with them!

Earlier models, such as the Jetstream and Cyclon, received some criticism as they could be tricky to service without tools underwater, the possible scenario being to clean an octopus that had been dragged through silt or similar. Again, in my opinion, this is a wrong statement when applied to the XStream. The XStream's second stage design is simplicity at its best. The cap at the front is a strong rubber cap which can be literally torn off with one hand in a second, shaken and stirred, and then replaced within a few more seconds, quicker if using both hands. I have done this underwater as an exercise, this is totally possible without tools. And it works with wet or dry gloves as well. See the following picture, it is rather self-explanatory:

Second stage with cover removed:

Also, with proper hose arrangement, i.e. breathing from your primary second stage on a long hose arranged across your body and around your neck, and your backup second stage placed directly beneath your chin, you really need to be crawling through mud before you get this regulator full of dirt! Personally, I can think of more pleasurable dives than that :-)

As for the use in backup stages which are placed in muddy parts in a cave, yes, you might want to look into other regs for other reasons than this. But as far as your primary and backup second stages go, this unit performs perfectly in just about any situation, delivering dry air in any swimming position (technically only perfect horizontal trim is necessary, but it's a good exercise to increase water comfort levels to swim on your back at 20m depth and keep the buoyancy level - at least in clearer waters you get a different perspective if nothing else ;-) 

All in all, we find this to be a fantastic cold-water regulator with excellent reliability. Needless to say, whatever works in cold water, works in warmer waters too. We've used ours everywhere from sandy beaches off Fiji to 4 degree cold water lakes in Germany and Austria.

 

FAQs - (from Poseidon's website):

Doesn't the Poseidon regulators have a higher interstage pressure?

The Jetstream and the Xstream both work at an intermediate pressure of 10 bar / 145 psi at 20 bar / 290 psi and at 8,5 - 9 bar / 123 - 130 psi at 300 bar / 4350 psi tank air pressure. This is the same intermediate pressure as most other brands.

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Other FAQs:

Isn't the upstream design a bad thing?

I would not say so. For starters, it is a very high performing regulator, delivering air in any position, regardless of your breathing pattern or your workload. This is always a good thing. Secondly, in the case of a first stage failure causing excessive intermediate pressure, the integrated overpressure valve in the Mk3 first stage will bleed off excessive gas, but BECAUSE of the upstream servo-valve technology, the second stage will still deliver gas in a breathable way - where conventional downstream regulators are likely to free-flow (and not really remaining breathable).

The front purge button looks like it could become depressed if using a scooter, no?

Please re-read the description or look at the drawings in the manual :-) The front area is a protective cover for the diaphragm, NOT the purge button. So yes, you can high-speed scooter with this one if you like - there are in fact YouTube Videos of guys scootering under the ice with this regulator, no issues there. The purge button is on the side of the device. 

Isn't it dangerous if your dive buddy doesn't know where the purge button is and accidentally presses the front cover?

Sorry, in that case you probably screwed up your pre-dive check. Also I would say that in an out of gas scenario, the person is going to grab your regulator and inhale immediately - something that works well with this regulator thanks to its non-directional design and incredibly small second stage volume.

Headquarters:

Poseidon Diving Systems
P.O. Box 8050
S-421 08 Västra Frölunda SWEDEN
Phone: +46 (0)31 734 2900
www.poseidon.se

Updates to the article:

This is the adapter - available from Poseidon for around $15:

New (german language) review of the Poseidon Deep 90 Mk3 double-set on tauchen.de:

Link to very favorable PDF review 

They attempted to cause it to freeze by using the purge button in a silly cold lake in Hemmoor without "success" :-)