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  1. #21

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    Here's the requested picture. 3/8" bungee around the neck as a choker for the upper bolt snap and a very short tail on the lower bolt snap.
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    NACD Cave DPV Cert # 666: Cave DPV Anti-christ

  2. #22

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    Quote Originally Posted by DA Aquamaster View Post
    Here's the requested picture. 3/8" bungee around the neck as a choker for the upper bolt snap and a very short tail on the lower bolt snap.
    Nice 1st stage, one of the best ever built

    "Not all change is improvement...but all improvement is change" Donald Berwick

  3. #23
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    Quote Originally Posted by Kelly Jessop View Post
    Nice 1st stage, one of the best ever built
    Thanks to Russel's guidance, I now have 10 mk10/g250s. I had one sitting in the closet I never serviced for 15 years because I stupidly thought "newer" regs were probably better


    Sent from my iPhone using Tapatalk


  4. #24

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    Quote Originally Posted by rddvet View Post
    Thanks to Russel's guidance, I now have 10 mk10/g250s. I had one sitting in the closet I never serviced for 15 years because I stupidly thought "newer" regs were probably better


    Sent from my iPhone using Tapatalk
    Good for you. I have a stockpile of pistons, springs and rebuilds.

    "Not all change is improvement...but all improvement is change" Donald Berwick

  5. #25

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    Quote Originally Posted by Kelly Jessop View Post
    Nice 1st stage, one of the best ever built
    We have a dozen of them. All our stage and deco regs are Mk 10 G250s.

    NACD Cave DPV Cert # 666: Cave DPV Anti-christ

  6. #26

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    Quote Originally Posted by DA Aquamaster View Post
    We have a dozen of them. All our stage and deco regs are Mk 10 G250s.
    Berman, Jablonski, Moon, and Cole tested the Mk10 vs Mk20. Took a set of doubles, and closed the isolator. With a port plug on the 1st stage missing, then opened the valves at the same rate. The Mk10 side drained well before the Mk20.

    "Not all change is improvement...but all improvement is change" Donald Berwick

  7. #27
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    Mar 2009
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    Panama City Beach, Fl.
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    I really don't get why people waste money on new regs when the older one's often outperform them.


  8. #28
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    Quote Originally Posted by bamafan View Post
    I really don't get why people waste money on new regs when the older one's often outperform them.
    Stupidity. For years I assumed the newer regs had to be superior. Then i started learning about metal barrels and parts internally compared to newer plastic parts. Then Sudge schooled me.

    I think nowadays its easy to assume and be correct that newer is generally "upgraded" with many products. When it comes to regs, thats often no true, apparently. I love how my mk10s perform.


    Sent from my iPhone using Tapatalk


  9. #29

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    A few thoughts on the Mk 10:

    1) The only cave diving related problem I have ever encountered on the Mk 5 or Mk 10 or on customer Mk 5s or Mk 10s has been the potential for the high pressure piston stem o-ring to start extruding into the gap between the piston stem and reg body. When this happens and the piston moves during it's normal cycle, it cuts a crescent shaped feather out of the o-ring and it doesn't take much of this to cause a slight leak. When that happens you get bubbles coming out of the ambient pressure chamber holes.

    This only happens in a) really high mileage Mk 10s that have some wear in this area in the reg body (and the brass body wears before the stainless steel piston stem) and/or b) in Mk 10s with looser than normal tolerances in this area. This also usually only happens at pressures around 3500-3800 psi. The Mk 10 was designed for 3300 psi, so it's not really a design flaw when the o-ring starts getting pinched at pressures above that.

    I've heard reports the Mk 10 Plus was designed for 4000 psi, and it's possible that the Mk 10 Plus first stage bodies were made or selected with tighter tolerances, but with the upgrade kits being sold to upgrade a Mk 10 to a Mk 10 Plus, at this point in time it would be very hard to tell the originals from a later model Mk 10 that was upgraded to Mk 10 Plus status.

    The good news is that unless you've got a severe case of piston stem o-ring pinching, it is usually not a problem at a 3000 psi service pressure, so the reg will still work great on an AL 80 stage bottle.


    2) Wear in this area of the reg body is the eventual killer of a Mk 5 or Mk 10. However, given that there are still 40 plus year old Mk 5s still in regular use, it takes a long time and a lot of use to wear one out if they have been properly maintained. None the less, this is why Scubapro developed the bushing system in the Mk 15 and then refined it in the Mk 20 and Mk 25. The plastic bushings are replaced annually or bi-annually at service, and prevent any wear to the reg body.

    The number two killer of a Mk 10 is corrosion or scoring in the reg body where the piston head O-rings seal against the body. Since the seating surface is in the reg body, if you get a pit there that causes a leak, the reg is pretty much done. You can try to resurface it with some skilled use of a hone and some very fine emery cloth but you are then also increasing the gap that has to be sealed by the single o-ring.

    The SPEC kit on the later Mk 5 and the Mk 10, when properly packed with silicone prevented any corrosion, but if improperly packed it could actually trap water and promote corrosion. Unfortunately, not all technicians were properly trained in packing a SPEC chamber. The process involved placing the silicone in the right spots in the reg body, and in the assembled piston and spring before installing the piston and spring in the reg body and screwing on the swivel cap on. Done right there were few voids and no voids in contact with metal surfaces. Done poorly, you could have voids next to a sealing surface which would eventually become water filled.

    The Mk 15, 20 and 25 have the seating surface in the swivel cap so any corrosion just requires a new swivel cap (a $25 part) and corrosion isn't a death sentence on those regs.

    In addition, with the Mk 15 Scubapro added a plastic wiper ring to keep the seating area clean and in the mid production Mk 20 this was changed to a pair of o- rings, one serving to keep the sealing area clean and dry, while the other does the actual sealing. The late Mk 20 piston carried over the Mk 25.


    3) Flow rates vary for the Mk 10 and the Mk 20 depending on what piston is in them. The Mk 10 piston for example evolved from a piston with a small hole in the head end to one with a larger cone shaped hole to improve the gas flow through the piston. In the Mk 10 Plus Scubapro added a rounded seating surface to the piston and a concave piston seat (basically the same arrangement used in the Mk 15, the Mk 25 and some of the Mk 20s). This didn't work so hot initially as seat life tended to be short and I found that I needed to replace the seat mid season when doing 130 plus dives per with both the Mk 10 Plus and the Mk 15. Eventually Scubapro got the material right and turned the Mk 10 into a serious performer, but there was a period of several years where I converted all my Mk 10 Plus first stages back to regular Mk 10s.

    The Mk 20 had three different pistons over it's career. The original Mk 20 piston was an all stainless steel piston with a knife edge seating surface, like the Mk 5, regular Mk 10 and the Mk 15. The mid production Mk 20s used a brass tipped stainless steel piston, and the brass tip used a rounded seating surface to improve flow rate (like the Mk 10). These brass tipped pistons were kind to the seat, but didn't lock up well and tended to wear in service. it's rare to find one of these now as most eventually failed in service (excessive IP creep) and were replaced with a later Mk 20 or Mk 25 piston. The later Mk 20 piston was a composite piston with a polymer head and a steel stem with an almost knife edge seat. This carried over to the Mk 25, and it changed very little with the Mk 25, the major change being a mirror polish on the stem to help prevent ice from stocking to it in cold water dives. The current Mk 25 piston will retrofit into any earlier Mk 25 or Mk 20, and in fact any Mk 20 could be upgraded to all the Mk 25 features, at least until Scubapro introduced the Mk 25 EVO, which uses different threads on the swivel cap.

    4) Functionally, my favorite cold water piston regulator was the early Mk 20 that could use the Mk 15 SPEC cap to enable the ambient chamber to be packed with silicone. The Mk 15/20 SPEC cap was much better than either of the Mk 10 SPEC systems (the early system had small 1/16" holes that leaked silicone, and the later one used a SPEC boot that fit in a groove around the ambient chamber holes, but did not allow for any expansion of the silicone when the piston moved) and it was a superb cold water first stage. The Mk 25 with any iteration of the TIS system, or the Mk 25 EVO just can't compete in cold water compared to an early Mk 20 with a SPEC boot.

    5) In terms of flow rate, the Mk 20 and Mk 25 are in fact vastly superior to the Mk 10 and Mk 10 Plus under test conditions, but it doesn't matter in the real world for two reasons:

    First, when Scubapro tests regs for flow rates, they are using high flow valves and a constant supply pressure. You don't find that in the real world. For example someone in a post above noted a comparison with a Mk 20 and a MK 10 on a manifold with the isolator closed and noted the performance (time to out of gas) was the same. That's the case because the flow rate of the manifold on each side was exactly the same, and was in fact the limiting factor. So once the first stage is flowing more gas than the valve or manifold can manage, it's just over kill.

    Second, 100 scfm is enough flow rate for any diving purpose. For example, the regular Mk 10 flowed around 100 scfm of gas at 3000 psi, and if I recall correctly the Mk 10 Plus improved this to around 125 scfm. Since that's already higher flow rate than most valves and manifolds can manage, the fact that a Mk 25 can flow about 270 SCFM out the side ports and about 300 SCFM out the end port is irrelevant. It's excessive performance that will never be used. To put that lowly Mk 10 100 scfm flow rate in perspective, the US Navy tested the Scubapro Pilot second stage at 1800 ft using a Mk 5 that had a flow rate around 96 scfm at 3000 psi.

    If you have a higher than average SAC of 1.0, and you average 3 second inhalations with 6 breathes per minute, even at 300 ft (10 atm) you only need a flow rate of about 33 scfm, and even if you're gas sharing with a similar 1.0 SAC rate diver, that's still only 66 SCFM. A Mk 10 Plus will manage twice that much gas - or in other words, it will support two divers with a 2.0 cfm SAC rate at 300 ft, even when they are both inhaling simultaneously. That's not even taking into account that trimix will flow through the reg about 20-30% more efficiently than air, depending on the helium content.

    The Mk 10 and Mk 10 Plus quite frankly will supply all the gas you'll ever need in a real world situation.

    ----

    But to be fair, even discounting the higher flow rate, the Mk 25 is better in a couple respects, such as a replaceable bushing system, the wiper ring on the piston head, the easy to replace sealing surface, and a lighter piston with a larger head with a slightly faster response time. However, the flow rate difference isn't a real world advantage and the Mk 25 won't do anything that a used Mk 10 first stage costing about $350-$400 less won't do just as well in real world conditions. Consequently the other improvements in the Mk 25 are just are not worth the extra expense, especially for technical divers who need primary and backup regs, multiple stage regs, and one or more deco regs.

    NACD Cave DPV Cert # 666: Cave DPV Anti-christ

  10. #30

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    Nice thoughts Larry. Some of the older gear that was used in cave diving a number of years ago still has relevance. I still find the Sherwood Magnums/Oasis 1st stages are probably one of the best sidemount regulators ever built, and the Dacor Turboflex fins are light weight,but have the kick of a powerfin in a small foot print.

    "Not all change is improvement...but all improvement is change" Donald Berwick


 

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