Apeks XTX50 Adjustable Second Stage

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The Apeks XTX50 Second Stage is an ultra-performance pneumatically-balanced downstream design second stage that comes with an inlet heat exchanger and a full metal valve barrel for excellent cold water tolerance.

Sometimes you feel like a nut... sometimes you don't. Apeks also offers a version of this second stage without the opening effort adjustment knob; the Apeks XTX40 is $50.00 lower in price but otherwise offers the same performance.

When purchased separately, individual regulator stages remain as factory configured by the manufacturer and final integration must, out of necessity, become a customer responsibility.

Apeks XTX50 Adjustable Second Stage

  XTX50 Second Stage - All Black Cover
  XTX50 Second Stage - All Black Cover Right and Left Inlet Orientations 2-Stage Purge Button Diver Changeable Exhaust Reversable 2nd Stages
  • Extreme performance pneumatically-balanced downstream design
  • Large progressive two-step purge operation and Comfo-bite™ mouthpiece
  • User adjustable opening effort resistance knob and venturi lever
  • Metal heat exchanger and barrel for excellent cold water tolerance to {36°F | 2°C}
  • Options for right or left inlet orientation - user changeable exhaust tee size

The Apeks XTX50 second stage is a pneumatically-balanced downstream design that results in smooth, easy breathing. The XTX50 purge button is large and easy to operate and features two-step progressive operation. Press the purge on the side for a lower flow rate, useful where more control is required such as filling lift bags, then press in the center for the full effect of the purge such as when clearing water. The large venturi lever has a soft touch rubber grip, which makes it easier to locate and use. Easy-to-grip opening effort adjustment knob keeps the diver in control. A heat exchanger which surrounds the valve mechanism, dissipates the cold caused by gas expansion while drawing in the warmth of the ambient water. The popular Apeks Comfo-bite™ mouthpiece by Aqualung greatly reduces jaw fatigue. The Apeks XTX50 primary second stage is black color with a larger wide exhaust tee and the Apeks XTX50 octo version is yellow color with a compact narrow exhaust tee. Other than their color, both the primary and octo versions of the XTX50 offer the same ultra-performance. When the DST first stage is paired with the XTX50 primary second stage plus a {30 in | 76 cm} hose, Apeks markets the package as the "XTX50 Regulator".

The XTX50 design supports an innovative user changeable exhaust tee. This system gives the diver the ability to change from the standard wide exhaust tee to an optional narrow exhaust tee (available separately) that makes the second stage more compact. The XTX50 is also a reversible design that can be converted from a standard right-handed hose inlet configuration to an uncommon left-handed configuration. Apeks describes the process of reconfiguring the regulator to a left-handed hose inlet as both quick and simple, however they recommend this be done by a regulator technician; see Product Attachments tab above for more information. FYI, Apeks also offers a version of this second stage without the opening effort adjustment knob; the Apeks XTX40 is $50.00 lower in price but otherwise offers the same performance.

Apeks brand regulators include a Limited Lifetime Warranty as long as they are inspected or serviced annually by an AQUALUNG AMERICA Authorized Dealer. This warranty covers the original owner against defects in parts or workmanship for the lifetime of the regulator and includes the Free-Parts-For-Life Program as outlined on their website.

More Information
Brand Apeks
SKU APX-RS132111
Weight 1.000000

Customer Reviews


What is the knob and lever on my second stage?

The knob and lever are used to alter the breathing characteristics of some types of regulator second stages. All our downstream design high performance second stages, including the DGX Xtra and D6, Dive Rite XT2 & XT4, MaresXR HR, and the Apeks XTX50 include a knob to adjust inhalation cracking pressure (aka opening effort.) Some second stages, including the DGX Xtra and D6 along with the Dive Rite XT2 & XT4 and Apeks XTX40 & XTX50, offer a lever to disable/enable venturi assisted inhalation. The Mares XR HR/VR/SXS stages use a unique Vortex Assisted Design (VAD) system that does not require a venturi lever. Upstream designs with a servo-assist valve, such as the Poseidon Xtreme, don't normally incorporate these features because the design inherently obviates most of the need for them. Many special application designs that are light duty, such as backup (aka 'octo', 'safe second', 'alternate', 'oxygen') and BCD integrated second stages, may omit the diver adjustable cracking pressure and/or the venturi assist features for the sake of simplicity.

The knob is for diver adjustment of the cracking pressure (aka opening effort) which is the inhalation force it takes to trigger the second stage valve to open and begin to flow breathing gas to the diver. Some people might refer to this as the 'breathing resistance' but this is a misnomer because once the gas starts flowing, adjusting the cracking pressure during inhalation will have minimal effect. On most high performance designs turning the knob all the way out (counter clockwise) will cause a slight hiss or dribble of free flowing gas and turning it all the way in (clockwise) will make it difficult to breathe from the regulator. Start by setting the knob in the middle of the adjustment range and then turn the knob to set the cracking pressure to your personal preference. Some divers will occasionally adjust it during the dive based on changes in their physical effort and depth, but most divers find a setting they like and never feel a need to change it. †

Many high performance second stage designs include a venturi assist feature that reduces breathing resistance by automatically increasing gas flow during inhalation. Regulators with the venturi assist enabled are prone to free flow if the second stage is not in the mouth. The venturi lever set in the pre-dive position (-) will substantially eliminate the tendency to free flow. Second stages in pre-dive mode WILL deliver breathing gas, but with some increased breathing resistance because the venturi assist feature has been disabled. On the primary second stage, you should push this lever in to the dive position (+) when you put the regulator in your mouth. On second stages not in the mouth during the dive the switch remains in pre-dive position; should circumstances require its use while in-water, once breathing from the regulator just switch the lever from pre-dive to dive mode.

The knob and the lever have related yet different functions, the knob determines how easy it is to start the breathing gas flowing to the diver and the lever determines how easy it is to maintain the breathing gas flow. Some lever designs are {predive| dive} with little or no range of adjustment to the venturi effect, however the adjustment knob by design always has a significant range of settings. Both can be set to minimize the possibility of free flow.

Some divers (especially those who use a breathing pattern called 'skipping') incorrectly believe that by using the adjustments to decrease the regulator performance they will conserve gas. In fact, improperly adjusted second stages have the opposite tendency to cause most divers to retain CO2 and increase their respiration rate thus gas usage while at the same time causing some discomfort and/or headache.

† You might be surprised to learn some experienced divers dislike having an adjustment knob on their second stage. They view the knob as an unnecessary option that is thought to be more of an entanglement hazard, certainly adds to the cost of the regulator and some just prefer a more streamlined second stage. Unnecessary? Yes, even when there is no external knob, the cracking pressure on downstream designs is always easily adjustable internally. On the surface, insert an in-line adjustment tool between the hose and the stage. Push the end of the tool into the adjustment slot then turn the thumbwheel on the tool at most an eighth for each adjustment while simultaneously depressing the purge button, then pressurize and experiment breathing on the regulator. Slowly iterate the adjustments until you find find the setting you like. Finally remove the tool, reconnect the hose and go diving. You may find differences in water, and if so you can repeat until the second stage is perfectly tuned for your preference. This an easy skill to learn, beneficial to know, and there are videos on the internet to show you how.