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The X650 second stage I obtained was mated to SCUBAPRO's latest version of the MK25 first stage, which now sports anti-icing fins and a new wound, stainless filter. I've used MK25s for technical diving for several years now and have never had a failure or a performance deficit.
Like the 400, the X650 was fitted with a dive/pre-dive lever that moves an internal flow-control vane. Leaving the lever in the dive position while moving around on the surface usually resulted in a dramatic demonstration of the regulator's response potential — an aggressive freeflow.
My usual modus operandi for this type of reg is to enter the water in pre-dive to prevent freeflows, then flip over after I'm comfortable and a few feet into the descent. As I swam into the spring vent against a stiff current, I dropped to 20 feet before switching to the dive setting and immediately felt the difference. Even though I'm usually pretty comfortable in the dim confines of a fast flowing underground spring, the near effortless breathing response of the X650 provided a notable calming effect.
Despite the regulator's sensitive surface tendencies in the dive setting, it did not freeflow at depth, even against the current. This was due to the lever configur-ation and the antisurge diaphragm — features carried over from the 400.
My human senses may not be as finely tuned and accurate as a robotic breathing machine, but I could certainly appreciate the comfort level the X650 provided as I dropped into total darkness well below the 100-foot mark. The regulator had what engineers would call a very flat response curve and a low work of breathing, which meant it responded quickly when you inhaled and didn't force air down your throat. However, it can really ramp up the flow rate when needed, and it allows you to exhale with minimal resistance.
In the past, I've been partial to SCUBAPRO's 250/600 series, even though the 400 was considered the ultimate for high performance, low-effort air delivery. The new X650 seems to combine the best qualities of both. It offers diver-adjustable inhalation effort like the 600, along with the below-the-mouth air chamber, the linear-coaxial flow valve and the fixed venturi-initiated vacuum assist of the 400.
The X650's poppet is smaller than on previous models, which enables faster response to inhalation demands. It is also fitted with an extra large exhaust valve, which accounts for the low exhalation effort. The streamlined case isn't just for looks; its position and low weight combine with the orthodontically designed contoured mouthpiece to minimize jaw fatigue.
SCUBAPRO X650
IMPRESSIONS: SCUBAPRO's best breathing regulator ever is certainly worthy of top billing. KEY FEATURES: Straight-coaxial flow valve, and the small poppet provides dynamic response to inhalation demand; the diaphragm and exhaust valve are positioned below the mouthpiece to reduce drag, weight and jaw fatigue; lighter weight also minimizes jaw fatigue; wide exhaust valve for reduced exhalation effort; diver-adjustable inhalation effort; and an orthodontically designed mouthpiece. MSRP: $549
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