ddub23 once bubbled...
I'm a new diver looking at several regs. Ones that I've been considering are:
1) Scuba Pro: MK25 S600
2) Aqua Lung Legend LX Legend LX
3) Oceanic Zeta/CDX5
What are the advantages between Piston or diaphram regulator? I will be doing mostly cold water diving so freezing may be a concern. Out of the three, the Zeta is the most compact and has a "servo assisted pilot valve." What exactly are we talking about?
I am look for a bulletproof reg that breathes effortlessly, and is reliable. I am willing to pay a little more for quality and piece of mind. Any input would be appreciated. Thanks.
Personally I have an Aqualung Legend LX and I love it. It breathes easy, it's dry, it's light and sturdy, maintenance friendly and it's based on a bulletproof and time proven design.
And I'll try to answer your other question about the "servo assisted pilot valve"
A pilot valve is just another mouse trap to open your 2nd stage for breathing. A "normal" downstream 2nd stage works like this: you breathe in, the diaphragm presses against a lever and the lever opens the valve allowing air to rush into the regulator. When the pressure is equalized the diaphragm returns to it's relaxed position and the lever closes and the air stops flowing.
Now imagine a hose going into the regulator with a little downstream valve on it but with a spring that's too light to stop it from free-flowing. Then put a little cap on that (like sticking a hose into a bigger hose with the end of the bigger hose blocked off. This is called an upstream 2nd stage with a pilot chamber (the pilot chamber is the air space inside the bigger hose). Upstream because the pressure holds the valve shut. Now imagine that the end of big hose has another small valve (the pilot valve) in it and that the pilot valve can tilt out of position to allow the higher pressure air in the pilot chamber to rush into the body of the regulator. When you breathe in, the diaphragm contacts the pilot valve. The pilot valve lets the pressure drop in the pilot chamber, the air pressure in the hose forces the main valve open and air runs into the regulator. When you stop breathing the diaphragm relaxes, the pilot valve returns to it's closed position the pilot chamber fills and pressurizes and this closes the valve. This is about as simple as I can make it sound without showing you a picture. As with most things there are several variations on this theme as well.
The point of doing this is that (in theory) you can make the regulator breathe easier while delivering large amounts of air. Poseidon regulators are well known for employing this technique. You can also design an upstream valve without the pilot chamber but in order to keep the valve closed you need to make the hole that lets the air into the regulator too small to perform well. There are other advantages to upstream valves as well. They're a maintenance friendly and they can handle varying intermediate pressures without adjustment. The second reason, in particular is the reason that most (if not all) 1st stages are upstream designs. Varying tank pressures demand a design that can easily handle this.
On the down side, pilot valves are associated with "chatter" or "shudder" when breathing (especially when breathing lightly or in shallow water). It's inherent in the design and there isn't too much you can do about it. Some people also notice a little (emphasis on little) delay between starting to inhale and getting air. It's probably something you get used to so I wouldn't really call that a reason to not buy one. They do feel "different" than "normal" regs so if you're thinking of buying one I'd give it a test dive or 2 before making your final decision.
I hope this answered your question.
R..
ut: )
