how important is a balanced reg?

[Scubakevdm]

I said that it wouldn't be good in cold water because it doesn't have the "Anti-Freeze" system that is on the Mk25's. Although it does have the T.I.S (thermal insulation system?)

The TIS on the Mk2 consists of a coating applied to the spring. The Mk25 has spring paint, an ice squeegee on the piston shaft and fins on the outside that increase the surface area. I think that the Mk25 is still more susceptible to freeze-ups though because it flows more. There is a very disticnt possibility that I'm wrong about this though. Anyway, the Mk16 is the one you want for cold water.

 

[Piston]

"The TIS on the Mk2 consists of a coating applied to the spring. The Mk25 has spring paint, an ice squeegee on the piston shaft and fins on the outside that increase the surface area. I think that the Mk25 is still more susceptible to freeze-ups though because it flows more. There is a very disticnt possibility that I'm wrong about this though. Anyway, the Mk16 is the one you want for cold water."

I actually think, no to say your wrong or anything, that by increasing the flow of water through the Mk25 helps in prevention of free flows. Water is an excellent thermal conductor. I reciently went on a dive and the water temp was 36f, I was using a Mk25 AF/G250HP and my buddy was using a Mk25/G250HP and his regulator started free flowing at 85ft. He tried adjusting the regulator, but no luck so dive done. Of corse I agree with you 100% if you want a cold water Scubapro go with the Mk16.

 

[scottfiji]

thanks for everyone's help so far, I'm definitely learning a lot, you guys are great. One question - what is considered "cold water" from a regulator perspective? The water here in so-cal is 54-59 degrees...that mean I need a cold water reg? (One person already answered this, I just wanted to see what others thought, thanks)

 

[Scubakevdm]

increasing the flow of water through the Mk25 helps in prevention of free flows. Water is an excellent thermal conductor.

This is true, however when I said the 25 flows more I was talking about air, not water. I'm not always as clear as I mean to be. Soon DA Aquamaster will be along though, I bet. He'll know which is better cold, 25 or 2.

 

[Scubakevdm]

thanks for everyone's help so far, I'm definitely learning a lot, you guys are great. One question - what is considered "cold water" from a regulator perspective? The water here in so-cal is 54-59 degrees...that mean I need a cold water reg? (One person already answered this, I just wanted to see what others thought, thanks)

Below about 45 degrees. Actually, I consider water below 82 degrees cold, but regulators don't care until mid 40's. Depth and tank pressure also play a role in freeze up, so there's a combination of things together that matter. But for all intensive purposes I don't think very many regs freeze up in L.A.

 

[Piston]

O,
O.K. thanks for clearing that up Scubakevdm. Actually the Navy Dive Manual considers "cold water" to be 60f and below. Other books consider it anything below body temp. Everyone is different.

 

[DA Aquamaster]

SP's definition of cold water is 50 degrees and the Mk 25 does well at that temp. Much below that though and it potentially becomes a problem, particularly with high pressure tanks. With the Mk 25, the TIS system is not entirely adequate in very cold water (below 45 degrees) due to it's high flow rate (around 300 SCFM). Locally, 50 degrees is warmer than it ever gets below 100 ft. where the late August bottom temps are maybe 45-46 degrees.

On the other hand, the TIS system in the Mk 2 Plus works very well in cold water and divers in this area ice dive with them quite successfully. The Mk 2 Plus has a much lower flow rate that reduces the effects of adibatic cooling on the first stage.

That lower flow rate however means that it can become possible to over breathe the regulator in deep or demanding conditions. I would not use a Mk 2 below 130 ft (with air at least, they do quite well with trimix) or in conditions with heavy current, etc where divers may find themselves breathing extremely hard. With an unbalanced piston design, the orifice size and the resulting flow rate has some practical limitations. A larger orifice means higher flow rate, but also generates more downstram force on the seat and consequently requires a larger piston head to keep the IP change within reasonable limits across the range of tank pressure. The Mk 2 Plus uses a larger psiton head than the earlier Mk 3 and is better in terms of both flow rate and IP stability, but is still nowhere close to the balanced Mk 16 or Mk 25 in terms of performance and is probably only in the 80-90 SCFM range.

The Mk 2 and the R190 or R380 second stage can be adjusted to breathe very well but the IP drops from around 145 psi at 3000 psi to around 125 psi at 300 psi. This means cracking effort increases slightly as tank pressure drops. It does not really become noticeable until the tank pressure is close to 500 psi and even then it is not really noticeable unless you focus on it.

With a balanced second stage on a Mk 2 Plus there would be very little difference at all in cracking effort as the balance chamber in the second stage would compensate for the decrease in IP. But SP does not package the Mk 2 Plus with a balanced second stage and you would have to special order it with a balnced second stage like the G250, S550 or S600.

If you need both cold water perfromance (below 45 degrees) and good performance at depth, the Mk 16 is the way to go. It has a flow rate around 170 SCFM and also performs well in water as low as 2 degrees. It incorporates the same basic TIS system with a teflon coated mainspring and also has a very open ambient chamber that provides excellent heat transfer. These are also used extensively by cold water and ice divers in my particular neck of the woods.

 

[bigredbill]

The other issue which you might run into with an unbalanced first is that tuning on the 2nd stage could become more problematic. Probably not a big deal on the rig you are looking at because you have a way to tune/detune the 2nd, but if you are looking at a rig where the 2nd does not have a diver adjustable control, getting the tuning just right can be a bit of a pain. The reason is because the 2nd is also unbalanced, and it is subject to perform differently at differing IP pressures. If you get a heavy fill, for example, 3200 lbs instead of 3000, you are likely to lose most of the "extra" free air in freeflow, because the 2nd will have been tuned to work at 3000 lps, which translates to a higher IP pressure for an unbalanced reg.

That is the real difference you will see in performance - in an unbalanced reg the pressure in the hose that connects the 1st and 2nd stage will have a greater variation in pressure, and it is why tuning can be more difficult.

Having said that, I've dove all over the world on and old Scubapro Mark III - -an unbalanced piston reg, with an unadjustable 2nd stage, so your choice should work just fine!

 

[northcoast_diver]

The MK2 and R190 are very good regulators. They are easy to work on and easy to set up. A good technician could set them up to breath very nicely for normal recreational diving depths and I'll bet most people would not be able to tell the difference between the MK2 and a more expensive balanced regulator. (Again, normal recreational diving depths.)

If you can get this setup used at a LDS during their annual rental gear sell-off, then it would be a pretty good initial investment. In the future, if you decide to get more sophisticated gear, this then can become your pony reg, or your shallow stop, rich mix deco bottle reg.

 

[scubatoys]

The reason is because the 2nd is also unbalanced, and it is subject to perform differently at differing IP pressures. If you get a heavy fill, for example, 3200 lbs instead of 3000, you are likely to lose most of the "extra" free air in freeflow, because the 2nd will have been tuned to work at 3000 lps, which translates to a higher IP pressure for an unbalanced reg.

That is the real difference you will see in performance - in an unbalanced reg the pressure in the hose that connects the 1st and 2nd stage will have a greater variation in pressure, and it is why tuning can be more difficult.

Ooops... never mind...