confused about reg types

[emoreira]

Hi, I'm a new diver with only 39 logged dives.
I've been renting regs and BCDs for all the dives and I had bad experiences, mainly with BCDs.
I have already bought a brand new BCD and now I'm going for a reg.
I've taken the speciality course Deep Diving. In the SSI deep diving book there is a specific mention about the regs. They say that for deep diving (within recreational limits) the diver should use a "Balanced" 1st stage regulator to ensure the air volume at deep, even in the case of sharing air with your dive buddy.

But watching the regs descriptions I find that there are basically 2 types :
a) piston type
b) diaphragm type

I've seen also descriptions as "2nd stage diaphragm balanced", "1st stage diaphragm balanced", "piston balanced".
Somewhere I've seen that "modern 1st stage regs" are Piston type, but Scubapro MK17 is diaphragm type and in the web page mentions "balanced diaphragm first stage regulator" (MK17/ S555 - SCUBAPRO-UWATEC) while the MK25 is piston type (MK25/A700 - SCUBAPRO-UWATEC).
YouTube - SCUBAPRO MK25 and MK17 First Stages in 3D

So, "balanced" seems not to be an attribute of the piston type regs.
Diaphragm is made of rubber ? How long is it supposed to last ?
Diaphragm regs are recommended to dive in cold/muddy waters because water do not come into the reg to sense outside pressure, but cold water and mud contact the diaphragm.

Also, there seem to be no "unbalanced" regs now or at least for the last years.

Buying used is an issue, the information regarding the specs of a discontinued reg is hard to find and the prices for the new regs are prohibitive for my budget.

 

[firelaw]

pretty good discussion of the technical point at
Diaphragm and Piston First Stages, what's the difference?

I own 7 regulators for my family. All US divers Aqualung for service simplicity. 1 calypso, 3 se3 3 SEA4
mix of new and used 2nd stages, a mix based on personal preference. (my wife loves her beuchat, ever try to get one serviced?) Scubapro is the other ultra reliable choice

Aqualung and Scubapro equipment can be serviced everywhere in the world. Its a huge advantage. All the USD diaphragm regulators use the same internal parts so used regulators are fine if you have a good tech. Best deals I ever got were used regs from my "Local Dive Shop" till it went out of business. I have bought full sets Reg,octo,depth and spg for $120 on Ebay without any problem.

 

[emoreira]

Thanks for the link. It's almost what I was needing to clarify.

 

[muddiver]

I think that you would be hard pressed to find an unballanced regulator today in the mix of new designs.

I use Sherwoods for my simple, shallow water diving and they are ballanced piston type regulators for very long ago. They are also environmentally sealed, yet they are not diaphragm regulators. They work just fine and when tuned correctly they breath the same at any pressure.

With modern designs it really boils down to availability of parts (i.e. service) where you live and where you dive. Don't get cought up in the details unless you are going to do Tech diving and you also need to standardize you gear with a group (look up DIR and UTD).

 

[nidankempo]

Oceanic still makes an Unbalanced Piston Regulator the SP-5 . I use this when I am doing skills in the pool so the chlorine doesnt destroy my better reg set. AFAIK this is the only Unblanced Piston on the market at this time.

 

[a22shady]

Best the about the Diaghram MK17 is it sealed. a lot less likely to free flow due to cold water and great for contaminated or dirty waters and nothing can get inside.

Pistons are nice on paper they will show that they flow more air. I have both styles and used both and have yet to notice a difference when breathing. I stay with Diaghram as I dive northeast in cold waters.

Atomic has something of a Hybrid with a Sealed Piston. All though its not a truw sealed like the MK17, The atomic is sealed by closing off the holes and filling the chamber with an anti-freeze gel "Tribolube". But I have had all these reg's in waters as low as 36F with no issues But I have seen an MK25 free flow at waters that cold.

So if your doing cold water would recomend a diaghram MK17/ or Atomic sealed Piston. if it's warmer waters any of them will work.

 

[keyshunter]

Oceanic still makes an Unbalanced Piston Regulator the SP-5 . I use this when I am doing skills in the pool so the chlorine doesnt destroy my better reg set. AFAIK this is the only Unblanced Piston on the market at this time.

Several companies have unalanced piston first stage regs on the market. These are usually meant to be entry level or special purpose regs. For example, Aqualung Calypso, Scubapro MK 2+, Sherwood Brut, Cressi Sub AC2, Mares R2...

 

[LeadTurn_SD]

....In the SSI deep diving book there is a specific mention about the regs. They say that for deep diving (within recreational limits) the diver should use a "Balanced" 1st stage regulator to ensure the air volume at deep, even in the case of sharing air with your dive buddy.....

There is a common misconception about how balanced and unbalanced regulators effect performance.

All scuba regulators, balanced and unbalanced, are depth compensating. You could not dive with them it they were not. They are designed to automatically compensate for increasing water pressure.

Unbalanced 1st stages however will begin to supply a little less pressure to the 2nd stage when the tank is nearly empty. A balanced 1st stage will supply a fairly stable pressure to the 2nd stage, almost up to the point the tank is empty.

Seconds stages can also be "balanced" or "unbalanced".

I have not read the SSI book you refer to, but I would bet what they meant to say was you want a high performance regulator (one that can supply high flow rates) for deep diving. The unbalanced piston 1st stages currently on the market are simply lower perfomance regulators (they are the entry level regulators from each company that makes them). I don't know if it has more to do with their basic, simple and compact design.... but could an unbalanced piston be designed with the same flow rate as a Scubapro Mk25?? I'm not an engineer, and have no idea. And the balanced designs are easy to produce and offer the advantage of a stable intermediate pressure..... who would want to design a high performance unbalanced 1st stage these days?

Modern balanced piston or diaphragm 1st stages, and good quality balanced or unbalanced 2nd stages will work just fine for deep diving.

Unblanced piston designs are just fine for recreational diving.

Best wishes.

 

[aquaregia]

If you have a balanced 1st stage, there shouldn't be much difference between a balanced and unbalanced 2nd stage right? I know the IP will still vary a little, but won't it be very slight?

 

[LeadTurn_SD]

The "usual suspects" here in the regulator board can answer this better than I can, but I'll take a stab:

Modern balanced 1st stages will keep the IP very stable, regardless of tank pressure (until the pressure gets very low, I believe).

Balanced 2nd stages are really semi-balanced (if they were completely balanced, they would lose the ability to act as a downstream overpressure "relief" valve in the event of a high pressure seat failure in the 1st stage). Balanced 2nd stages are by and large "air balanced", and this allows them to use a lighter spring to keep the demand valve closed, compared to an unbalanced 2nds stage which relies 100% on spring pressure to close the valve. My understanding (which may be flawed) is that using a lighter spring offers some advantages, one being possibly lower breathing effort after the demand valve is "cracked" open (I may have this wrong).... however, well-designed unbalanced 2nd stages with a efficient venturi effect (Mares 2nd's with the VAD bypass tube springs to mind) can breath as well as balanced 2nd's.

So to answer your question, if you have a balanced 1st stage, there should not be much difference between balanced and unbalanced 2nd stages, as long as they are high quality and tuned properly.

Best wishes.