Combining an UNBALANCED 1st stage with a BALANCED 2nd-stage, what would I experience

[scubafanatic]

If I were to combine an UNBALANCED 1st stage with a BALANCED 2nd stage, what would happen ? What would one experience with respect to things like breathing effort during the course of the dive (full tank vs low/empty tank) Would IP increase or decrease (and by how much ?) and would it have any real world effect on breathing ease/effort ?

Thanks in advance !

Karl

 

[redacted]

If I were to combine an UNBALANCED 1st stage with a BALANCED 2nd stage, what would happen ? What would one experience with respect to things like breathing effort during the course of the dive (full tank vs low/empty tank) Would IP increase or decrease (and by how much ?) and would it have any real world effect on breathing ease/effort ?

Thanks in advance !

Karl

Unless you are deep and working hard, you should not notice much effect. The volume capability of unbalanced 1sts could come into play in situations like that. A good balanced 2nd may make it hard to detect the decrease in IP of an unbalanced piston until it gets quite low on gas.

I often pair a Mk2 with a G500 on my pony bottle.

 

[scubafanatic]

Unless you are deep and working hard, you should not notice much effect. The volume capability of unbalanced 1sts could come into play in situations like that. A good balanced 2nd may make it hard to detect the decrease in IP of an unbalanced piston until it gets quite low on gas.

I often pair a Mk2 with a G500 on my pony bottle.

I just bought a 'mint' vintage Scubapro MK 2, yoke style (as well as a NIB DIN adapter for the MK 2). I thought it would be cool to at least have a DIN adapter available if I ever wanted to dive a DIN vintage regulator. I might combine the MK 2 with a couple SP 109s/156s that I've had upgraded to balanced adjustable.

So, if I assemble this 'combo', would it be a reg set that I can safely dive in any recreational setting ? (I'm typically a warm water tropical diver, max depths 130' - 150') I do prefer to dive on the deeper side and will spend a lot of time in the 90' - 130' range.

 

[ams511]

I have dove a MK-2 with a G200B and it worked well. However, I was only at depths half of what you are talking about. The MK-2 is a great first stage and easy to rebuild but its flow rate is not the best. Is it safe, probably so. If you want to be on the safe side and dive a vintage din regulator deep, then why not find an older MK-10 spec to convert to din.

 

[scubafanatic]

I have dove a MK-2 with a G200B and it worked well. However, I was only at depths half of what you are talking about. The MK-2 is a great first stage and easy to rebuild but its flow rate is not the best. Is it safe, probably so. If you want to be on the safe side and dive a vintage din regulator deep, then why not find an older MK-10 spec to convert to din.

I've got some MK5's, and recently acquired 2 MK 5 DIN adapters (used), so that is also an option. Getting DIN adapters for MK 5's is very hard though, so I thought it might be nice to get the MK 2 as I was able to locate a NIB DIN adapter for it. Seems like opinion here overall is that the MK 10 is a step backwards from the MK 5, so I wasn't in a super hurry to go the MK 10 route, but I suppose that's still an option.

With respect to flow rate from the 1st stage, I get the impression even an 'old' MK 2 (fully tuned.serviced) should put out more air than one or 2 divers would ever really need, in the real world, or is this incorrect ?

 

[dumpsterDiver]

I had a buddy who used the MK-2 to spearfish to depths of around 140 ft. Spearfishing and chasing fish can involve high demands. I always used higher end SP first stages and I asked him how his performed- since it was so small (and cheap).. He indicated it was very reliable (with infrequent service requirements) and said it always felt like it gave him all the air he wanted.

I bought 2 of those MK-2's about 5 years ago. One has been used as a pony bottle first stage for like 5 years with zero service and zero problems. The spare one is still in a box somewhere. Mine has not been used through thousands of breathing cycles, but it has been "used" for several hundred dives in saltwater in that time.

 

[scubafanatic]

I had a buddy who used the MK-2 to spearfish to depths of around 140 ft. Spearfishing and chasing fish can involve high demands. I always used higher end SP first stages and I asked him how his performed- since it was so small (and cheap).. He indicated it was very reliable (with infrequent service requirements) and said it always felt like it gave him all the air he wanted.

I bought 2 of those MK-2's about 5 years ago. One has been used as a pony bottle first stage for like 5 years with zero service and zero problems. The spare one is still in a box somewhere. Mine has not been used through thousands of breathing cycles, but it has been "used" for several hundred dives in saltwater in that time.

Simple reliability was another consideration, could use my MK 2 as part of my travel 'save-a-dive' kit, something that I could really count on, yet also something that still has decent breathing performance throughout my expected dive profile 'envelope'

---------- Post added March 1st, 2015 at 10:48 PM ----------

I had a buddy who used the MK-2 to spearfish to depths of around 140 ft. Spearfishing and chasing fish can involve high demands. I always used higher end SP first stages and I asked him how his performed- since it was so small (and cheap).. He indicated it was very reliable (with infrequent service requirements) and said it always felt like it gave him all the air he wanted.

I bought 2 of those MK-2's about 5 years ago. One has been used as a pony bottle first stage for like 5 years with zero service and zero problems. The spare one is still in a box somewhere. Mine has not been used through thousands of breathing cycles, but it has been "used" for several hundred dives in saltwater in that time.

Simple reliability was another consideration, could use my MK 2 as part of my travel 'save-a-dive' kit, something that I could really count on, yet also something that still has decent breathing performance throughout my expected dive profile 'envelope'


I wonder if your buddy was using a balanced or unbalanced 2nd stage though ?

 

[ams511]

I've got some MK5's, and recently acquired 2 MK 5 DIN adapters (used), so that is also an option. Getting DIN adapters for MK 5's is very hard though, so I thought it might be nice to get the MK 2 as I was able to locate a NIB DIN adapter for it. Seems like opinion here overall is that the MK 10 is a step backwards from the MK 5, so I wasn't in a super hurry to go the MK 10 route, but I suppose that's still an option.

With respect to flow rate from the 1st stage, I get the impression even an 'old' MK 2 (fully tuned.serviced) should put out more air than one or 2 divers would ever really need, in the real world, or is this incorrect ?

The reason I recommended the MK-10 over the MK-5 is because the MK-5 dins are hard to find. I believe someone has found a workaround on this. If you have MK-5 dins then I would go that route. The MK-5 is only slightly more difficult to rebuild but watch out for the brass turret nut if you have one I would swap it out with the stainless version. From what I remember DA Aquamaster had a post comparing the MK-5 and the MK-10 and from what I remember in some categories the MK-5 was better and in some the MK-10. Whether the differences matter in the real world is anyone's guess.

 

[scubafanatic]

The reason I recommended the MK-10 over the MK-5 is because the MK-5 dins are hard to find. I believe someone has found a workaround on this. If you have MK-5 dins then I would go that route. The MK-5 is only slightly more difficult to rebuild but watch out for the brass turret nut if you have one I would swap it out with the stainless version. From what I remember DA Aquamaster had a post comparing the MK-5 and the MK-10 and from what I remember in some categories the MK-5 was better and in some the MK-10. Whether the differences matter in the real world is anyone's guess.

No worries, over time I've been having all my MK 5's upgraded to the SS turret nut. Yes, DA Aquamaster was a real resource back in the day when he used to post here.

BTW, what would be the recommended IP for a MK 2 ? (seller has it set to 140 psi)

 

[halocline]

No worries, over time I've been having all my MK 5's upgraded to the SS turret nut. Yes, DA Aquamaster was a real resource back in the day when he used to post here.

BTW, what would be the recommended IP for a MK 2 ? (seller has it set to 140 psi)

140 is fine for the MK2; it can drop almost 20 psi over the supply range, so if you want 125 with a near empty tank, you would set it at 145-150 at 3000 PSI. Pairing a MK2 with a 109 is one of the most bulletproof, abuse-tolerant regulators you could ever get. As far as depth goes, I've had my MK2 down to around 130 feet and it worked fine. If you want to check out the difference between a balanced and unbalanced 2nd stage over the supply range on the MK2, just go on a dive with one converted 109 and one left unbalanced, both tuned for best performance at the top range of the IP. With a full tank you wouldn't tell any difference between the two 2nd stages, but as the tank empties you'd find a subtle but increasing difference on direct comparison. My experience with the MK2 is that you really notice the breathing getting stiffer under 500PSI but not really before. And it still provides plenty of air, just the cracking effort increases.