Apeks XTX40 DS4 DIN Scuba Diving Regulator

Apeks XTX40 DS4 DIN Regulator: A Balanced, Cold-Water-Ready First and Second Stage Set

The Apeks XTX40 DS4 is a complete regulator set, first stage and second stage, built around a pneumatically balanced second stage and a dry-sealed diaphragm first stage.

If you are a recreational diver moving beyond entry-level gear, or an experienced diver who wants a reliable workhorse that handles cold water and doubles well as an octopus setup, this regulator deserves a serious look.

First Stage: Diaphragm Design and Port Layout

The XTX40 uses a diaphragm-style first stage, which means the internal mechanism is isolated from the water around it by a sealed membrane.

This matters in two situations: cold water and dirty water. Because the working parts never contact the surrounding environment, the first stage is less vulnerable to freezing up or to silt and contaminants interfering with performance.

The first stage comes in a DIN configuration, which screws directly into the cylinder valve rather than clamping over it. DIN connections are more secure under pressure and are standard on most cold-water and technical diving cylinders in Europe and at many dive centers worldwide. If you are diving predominantly warm-water resorts with yoke-only tanks, check what your local operators supply before committing.

Port count is practical:

Four LP ports gives you room to run a primary second stage, an octopus, a BCD inflator hose, and a drysuit inflator without an adapter. Two HP ports cover a pressure gauge and a transmitter if you run a wireless console.

The first stage body uses a swivel turret, so you can rotate the port cluster to route hoses cleanly regardless of how your cylinder sits on your back.

Second Stage: Breathing Performance

The second stage uses a pneumatically balanced valve. In a balanced design, the opening force required to start airflow stays consistent regardless of cylinder pressure. You get the same breathing effort at the start of a dive as you do near the end of a tank. That consistency is one of the main reasons divers step up from unbalanced entry-level regulators.

Apeks rates the Work of Breathing at 0.85 Joules per Liter. Work of Breathing is the measurable effort your lungs put in to pull a breath through the regulator. A lower number means easier breathing. At 0.85 J/L, the XTX40 sits comfortably in the range where breathing should feel natural and unforced, even at depth.

The second stage also uses a new silicone exhaust valve, which contributes to that breathing performance by allowing exhaled air to exit cleanly with minimal back-pressure.

Venturi Control and Cold Water Performance

The second stage has an integrated Venturi lever with a redesigned ergonomic shape that reduces the chance of grit or sand getting into the mechanism. The Venturi effect, in simple terms, is the tendency of airflow through the regulator to amplify itself once it starts. In normal diving you want this working in your favor, making inhalation feel effortless. On the surface or in rough conditions, it can cause the regulator to free-flow (deliver air continuously without you inhaling), so the lever lets you dial it back when needed.

The environmental dry-seal system on the first stage directly addresses cold water. By keeping water out of the first stage internals, it significantly reduces the risk of a free-flow caused by ice forming inside the mechanism. The second stage is also rated for cold water use. If you dive in temperate or cold environments, this is a meaningful design choice, not a marketing addition.

Reversible Hose Configuration and the DCE System

The XTX40 includes two features that make it unusually adaptable for its class.

The Reversible Venturi System (RVS) allows the second stage to be configured for either right-hand or left-hand hose routing. The switch requires an authorized Apeks technician, so it is not something you adjust on the boat, but it means the regulator can be set up to suit your preference or to work cleanly as a dedicated octopus on whichever side your setup demands.

The Diver Changeable Exhausts (DCE) system lets you swap between two exhaust tee sizes yourself, without tools or a technician:

• Small exhaust tee makes the second stage more compact, which is useful when you configure it as an octopus or want a lower-profile backup.
• Large exhaust tee directs exhaled bubbles away from your field of view, which matters if you shoot underwater photography or video and want to keep your frame clear.

This is a practical detail that is easy to overlook, but if you do any photography or run a dedicated octopus rig, it is worth having.

Build and Construction

The second stage front cover uses two-shot high-strength plastic, a construction method that bonds two materials together to produce a cover that is both impact-resistant and lightweight. The part it protects, the demand valve mechanism, is the most mechanically vulnerable section of the second stage, so this is a sensible place to add protection.

The first stage has a polished chrome finish. The second stage matches with a bright chrome finish. Both are visually clean and consistent, which matters if you care about a tidy kit.

An optional swivel hose connection is available at extra cost. It allows the hose end at the second stage to rotate and pivot, which some divers find reduces jaw fatigue on longer dives by letting the mouthpiece sit at a more natural angle.

Who This Regulator Suits, and Who Should Look Elsewhere

The XTX40 DS4 DIN is a strong match if you are a recreational diver ready to invest in a mid-to-upper-tier regulator that will not need replacing as your diving develops. The cold-water sealing, balanced performance, and flexible port layout make it genuinely useful across a wide range of conditions.

It also works well as a dedicated octopus second stage thanks to the DCE small exhaust option and the RVS hose configuration.

If you dive exclusively in warm, tropical water from yoke-only rental cylinders, the DIN fitting will require an adapter. That is not a dealbreaker, but it is worth factoring in. If your diving is purely warm-water resort trips and you have no plans to dive in colder environments, a simpler regulator may cover everything you need.

If you are looking at this for technical or overhead-environment diving, note that the XTX40 is built for recreational and military/rescue use. Dedicated technical divers running decompression profiles on mixed gas should look at Apeks regulators specifically rated and serviced for those applications.