SCUBAPRO DOES MAKE A DIAPHRAGM-TYPE REGULATOR NOW, but this manufacturer still seems very committed to the piston-type design. The MK25AF piston first stage is a development of the successful MK20, with certain aspects now more fully addressing the needs of those who dive in cold fresh water. Where other manufacturers try to keep cold water away from the working parts of their regulators, Scubapro adheres to the philosophy that the small amount of warmth present in the water can be transferred to the regulator. To this end its designers have improved the flow of water over the working parts by increasing the size of the holes that give it access to the main spring. At the same time finned heat-exchangers have been added to the body of the first stage. These are said to help reduce any ice-creep that may occur, resisting its movement from the turret towards those holes. Scubapro also uses a patented thermal insulation system, or TIS, that is said to resist the possibility of moving parts getting jammed with ice. The MK25 first-stage has been available for at least six months but now Scubapro has released onto the market its top-of-the-range X650 second stage to go with it. At first glance it reminded me of the old, rattlingly good D400 in the way the working parts are positioned below the mouthpiece. However, there seem to be no rattles evident with the X650 and I am informed that the working parts have far more in common with the S600, so it can almost be thought of as that second stage reconfigured in an alternative shape. By dropping the works and the air chamber in which they are housed below the level of the mouthpiece, Scubapro designers have been able to make this unit less compact than the current S600 second stage, without it feeling as bulky when in the mouth. Presumably this larger-size chamber gives them the opportunity to go after an even further reduced work-of-breathing, although most top-end regulator performances are so good now that the manufacturers seem to be using ANSTI tests as a way of showing off. Witness the fact that so many manufacturers have products that can perform at less than one joule per litre, when the target minimum criterion is total work-of-breathing of anything less than 3 joules per litre. This regulator promises massive flow-rates too, should you need them. Well, I was impressed when Roger Bannister beat the four-minute-mile barrier, yet runners have been continually trimming that time ever since. Similarly, it's no surprise that manufacturers feel impelled to go after the best-performance record for their regulator designs. I'm more interested in what it feels like to breathe from, and here we leave the scientists and their proven tests and join the area of the purely subjective. And what's wrong with that? Credit where credit is due. The ANSTI test was needed and we should not forget that it was my predecessor Mike Todd and this magazine that first beat up the regulator manufacturers back in the late '80s, with tests using an early ANSTI machine. He got them to get off their fat donkeys and make us regulators that delivered what we needed at depth. You can take it as read that the Scubapro X650 delivers more than enough air for your needs. Like its siblings, the X650 has the usual venturi Â? dive/pre-dive switch designed to resist exponential free-flows when passing from air to water. There is also a breathing-adjustment knob which allows the user to adjust the cracking pressure, the effort needed to initiate an inhalation. I found both of these controls easy to use, even with a thickly gloved hand. The orthodontic mouthpiece is comfortable and easily switched for a replacement thanks to the unique Scubapro design of its clip. Nothing as crude as cable ties is used here. Under water, the manner in which the unit drops away past the chin gives the effect of using a very compact second stage indeed, and the angle at which the pressure-sensing membrane of the second stage is presented to the water meant that I could look directly into fast flows without the thing bubbling away like a well-shaken bottle of MÃ?et. The only problem I encountered was at the surface when, if I forgot to put the venturi Â? switch back to the Pre-dive position, I could suffer a free-flow of such magnitude that it made me feel I was getting air at full cylinder pressure out of the mouthpiece. I saw 40 bars of tank pressure go in almost as many seconds on my first unprepared foray into the water. Everyone thought that it was a first-stage failure. However, once I had got the idea that I had to be very cautious at the cusp between air and water, I was able to use it without problem. The X650 represents the ultimate Scubapro regulator, and unsurprisingly its price reflects this. The X650/MK25AF costs £399.
Scubapro UK 01256 812636
+ Very high performance, including massive flow-rate + User-friendly knobs and mouthpiece + Bubbles diverted away from face
- Can misbehave at the surface if it goes into free-flow