Scubapro MK18/G250 O2 clean
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Hello Spyder,
How high a percentage will you be using? If 40 percent or less, your regulator is probably fine just the way it is.
couv
How high a percentage will you be using? If 40 percent or less, your regulator is probably fine just the way it is.
couv
halocline
Contributor
I don't know if there's a dedicated 02 kit, but the rebuild kit for the MK18 is the same as the Mk16/17. So there might be a "nitrox" kit for that reg. Other than careful cleaning (in the right environment, I suppose) and reassembly with 02 safe lube and viton o-rings, what would you need? Is there a special seat material for that reg for high% O2? I'd be curious, but I would guess not.
If by some small chance there is an issue using the MK18, you could consider getting a used MK2, and using your G250 on that. The MK2 would be a breeze to keep O2 clean due to it's simplicity and lack of any dynamic o-rings exposed to HP air. Another nice thing about the MK2 for stage/deco use is that it is very tolerant of flooding in the HP area, if you keep your bottle turned off and somehow bumped the purge and flooded the 1st stage.
If by some small chance there is an issue using the MK18, you could consider getting a used MK2, and using your G250 on that. The MK2 would be a breeze to keep O2 clean due to it's simplicity and lack of any dynamic o-rings exposed to HP air. Another nice thing about the MK2 for stage/deco use is that it is very tolerant of flooding in the HP area, if you keep your bottle turned off and somehow bumped the purge and flooded the 1st stage.
Scubapro does not, to my knowledge anyway, offer an O2 clean kit for the Mk 18.
In the US you can still get the Mk 20 Nitrox upgrade parts and O2 clean a Mk 20 or Mk 25 for use with up to 100% O2 at 3500 psi.
In the UK you can get a Mk 2 Plus R295 Nitrox or a Mk 25 S555 Nitorx approved for use with up to 100% O2 at 200 bar pressures.
In my opinion, a diaphragm first stage like the Mk 18 makes a poor choice for a deco reg. In a piston design, you have minimal non metallic parts (a handful of o-rings, a seat and in the case of the Mk 25, two bushings) in contact with O2. However with any diaphragm design you have alarge diaphragm in addition to the normla o-rings and the entire seat and seat carrier is located upstream of the orifice constantly bathed in o2 at tank pressure.
In that regard a Mk 2 Plus is ideal as there is no high pressure O2 past the seat and all of the moving parts and all the dynamic o-rings (all 2 of them) are located in the intermediate pressure section of the reg.
Consequently, is an O2 fire occurs in a Mk 2 Plus, it is most likely going to be a flash fire that chars the o-rings and blows itself out as the total available fuel is quite low. There is a bit more to burn in the Mk 25 (larger seat and 2 bushings), but the total fuel available is again low compared to a diaphragm design with it's large diaphragm and the seat carrier with it's seat and related o-rings and backing rings.
That same fire if started in a Mk 18, or virtually any other diaphragm design would most likely be much larger, and would rupture the diaphragm making it a situation where the fire may not be totally contained inside the regulator.
In the US you can still get the Mk 20 Nitrox upgrade parts and O2 clean a Mk 20 or Mk 25 for use with up to 100% O2 at 3500 psi.
In the UK you can get a Mk 2 Plus R295 Nitrox or a Mk 25 S555 Nitorx approved for use with up to 100% O2 at 200 bar pressures.
In my opinion, a diaphragm first stage like the Mk 18 makes a poor choice for a deco reg. In a piston design, you have minimal non metallic parts (a handful of o-rings, a seat and in the case of the Mk 25, two bushings) in contact with O2. However with any diaphragm design you have alarge diaphragm in addition to the normla o-rings and the entire seat and seat carrier is located upstream of the orifice constantly bathed in o2 at tank pressure.
In that regard a Mk 2 Plus is ideal as there is no high pressure O2 past the seat and all of the moving parts and all the dynamic o-rings (all 2 of them) are located in the intermediate pressure section of the reg.
Consequently, is an O2 fire occurs in a Mk 2 Plus, it is most likely going to be a flash fire that chars the o-rings and blows itself out as the total available fuel is quite low. There is a bit more to burn in the Mk 25 (larger seat and 2 bushings), but the total fuel available is again low compared to a diaphragm design with it's large diaphragm and the seat carrier with it's seat and related o-rings and backing rings.
That same fire if started in a Mk 18, or virtually any other diaphragm design would most likely be much larger, and would rupture the diaphragm making it a situation where the fire may not be totally contained inside the regulator.
Additionally, for 50% O2 you will be in relatively shallow depths. No need for a high performance 1st stage there. The MK2 is also very dependable, something you definitely want in a deco reg.
c
c
Couv makes a good point that I forgot to mention.
Some techncial divers will insist that your regs should all be identical. There are a few rationales that are used to Justify that belief:
1. Commonality of parts for field repairs
2. Interchangeability for different roles
3. Interchangability during a dive
#1 is only relevent if you have the tools, parts and ability to service your own regs. I do and in the last 10 years averaging 100 plus dives per year, I have had a need to do anything more than adjust a reg during a diving day just once and that was because I had put the annual service off a lot longer than I should have. Maintaining your gear properly makes this a moot point.
What I do now however is match the IP on all my first stages so that any of my second stages can be switched to any first stage which is a quick fix for a second stage problem.
As for number 2, I am a firm believer in using regs that are optimum for each application. For back gas and stage bottle regs (that may be used at maximum depth or for travel gas at intermediate depths) I want a reg with enough flow to handle the high demands at depth. In that application, a flow by piston design is inadequate. A fully sealed high performance diaphragm reg on the other hand, may be great at depth on cold water dives, but it is not well suited to deco with high percentage O2 mixes. A high performance balanced piston reg like the Mk 25, is great at depth and, properly cleaned, is fine with high percentage O2 deco mixes. So if you adhere to the dictum that all your regs need to be interchangeable bewteen backgas, stage and deco applications, you need to be using balanced piston regs.
Personally, I see no need for that level of interchangeability. I ensure all my regs are DIN and have the same IP, then as noted above I bring along a spare O2 cleaned Mk 10 G250. The first and/or second stage can do duty as a back gas reg to replace the Mk 17 G250V's I use there, or it can serve as a deco reg to replace the Mk 9 G250's and Mk 10 G250's I use in that role.
I could use Mk 10's Mk 15, Mk 20's or Mk 25's for everything, but I prefer the dry sealed MK 17 as I dive cold water on a regular basis, and the Mk 25 is less than 100% reliable in water colder than about 45 degrees while the Mk 1 is nearly bullet proof even at depth at 32 degrees. Similarly, a MK 10 is not reliable in very cold water unless you use the SPEC kit, and that would require Christolube or Tribolune rather than silicone in the ambient chamber to keep the reg O2 clean. That is both expensive and messy, especially on a large number of regs.
The "one reg that can do everything" approach does make sense if you, your team or dive group did expedition or exploration dives where on any given dive, you may need x number of stage regs and y number of deco regs where x an y vary a lot from dive to dive, but for the rest of us, having a spare that can do either will cover it.
I am not a fan of #3. Swapping a reg in the water is in my opinion a last resort to access the last bottom or deco gas I have access to. With proper lost gas planning you should have access to enough gas to complete the dive and required deco without swapping a reg. If you remove a reg underwater to swap it to another tank you will flood it and there is a risk it will fail during the dive. This is a very small risk with piston regs, but is a larger risk with diaphragm risks, so again if you feel number 3 is important, use piston regs.
Now where it get confusing, is that many technical divers use dipahragm regs and believe in and promote 1, 2 and 3 - despite the fact that 2 and 3 are problematic with diaphragm regs. Some of the issue may be that one of the agencies pushing 1 2 and 3 used to also promote using SP balanced piston regs (where 1,2 and 3 worked) but some key people had a falling out with SP over money/sponsorship issues and switched to Apeks (diaphragm designs where 2 and 3 are problematic.) They have the right doctrine from their perspective, but are just not fully aware of the pros and cons of various reg designs as it related to that doctrine.
Some techncial divers will insist that your regs should all be identical. There are a few rationales that are used to Justify that belief:
1. Commonality of parts for field repairs
2. Interchangeability for different roles
3. Interchangability during a dive
#1 is only relevent if you have the tools, parts and ability to service your own regs. I do and in the last 10 years averaging 100 plus dives per year, I have had a need to do anything more than adjust a reg during a diving day just once and that was because I had put the annual service off a lot longer than I should have. Maintaining your gear properly makes this a moot point.
What I do now however is match the IP on all my first stages so that any of my second stages can be switched to any first stage which is a quick fix for a second stage problem.
As for number 2, I am a firm believer in using regs that are optimum for each application. For back gas and stage bottle regs (that may be used at maximum depth or for travel gas at intermediate depths) I want a reg with enough flow to handle the high demands at depth. In that application, a flow by piston design is inadequate. A fully sealed high performance diaphragm reg on the other hand, may be great at depth on cold water dives, but it is not well suited to deco with high percentage O2 mixes. A high performance balanced piston reg like the Mk 25, is great at depth and, properly cleaned, is fine with high percentage O2 deco mixes. So if you adhere to the dictum that all your regs need to be interchangeable bewteen backgas, stage and deco applications, you need to be using balanced piston regs.
Personally, I see no need for that level of interchangeability. I ensure all my regs are DIN and have the same IP, then as noted above I bring along a spare O2 cleaned Mk 10 G250. The first and/or second stage can do duty as a back gas reg to replace the Mk 17 G250V's I use there, or it can serve as a deco reg to replace the Mk 9 G250's and Mk 10 G250's I use in that role.
I could use Mk 10's Mk 15, Mk 20's or Mk 25's for everything, but I prefer the dry sealed MK 17 as I dive cold water on a regular basis, and the Mk 25 is less than 100% reliable in water colder than about 45 degrees while the Mk 1 is nearly bullet proof even at depth at 32 degrees. Similarly, a MK 10 is not reliable in very cold water unless you use the SPEC kit, and that would require Christolube or Tribolune rather than silicone in the ambient chamber to keep the reg O2 clean. That is both expensive and messy, especially on a large number of regs.
The "one reg that can do everything" approach does make sense if you, your team or dive group did expedition or exploration dives where on any given dive, you may need x number of stage regs and y number of deco regs where x an y vary a lot from dive to dive, but for the rest of us, having a spare that can do either will cover it.
I am not a fan of #3. Swapping a reg in the water is in my opinion a last resort to access the last bottom or deco gas I have access to. With proper lost gas planning you should have access to enough gas to complete the dive and required deco without swapping a reg. If you remove a reg underwater to swap it to another tank you will flood it and there is a risk it will fail during the dive. This is a very small risk with piston regs, but is a larger risk with diaphragm risks, so again if you feel number 3 is important, use piston regs.
Now where it get confusing, is that many technical divers use dipahragm regs and believe in and promote 1, 2 and 3 - despite the fact that 2 and 3 are problematic with diaphragm regs. Some of the issue may be that one of the agencies pushing 1 2 and 3 used to also promote using SP balanced piston regs (where 1,2 and 3 worked) but some key people had a falling out with SP over money/sponsorship issues and switched to Apeks (diaphragm designs where 2 and 3 are problematic.) They have the right doctrine from their perspective, but are just not fully aware of the pros and cons of various reg designs as it related to that doctrine.
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Scubapro MK18
