73diver
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Scubapro MK7 OK at 3000psi?

Sat Oct 05, 2013 9:35 pm

I have two Scubapro MK7's purchased around 1981. Neither have a '3000' stamped on them. I have used these on 3000# tanks quite a bit with no problem. Is there a significant difference between the MK 7's with and without the '3000' stamp? The LDS will not send my steel tanks for hydro because they are deemed too corroded so I have been renting 3000# aluminum. Some of the people that I dive with have been grumbling about me using the MK7's with 3000# tanks. Any advice? Thanks.

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luis
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Re: Scubapro MK7 OK at 3000psi?

Sat Oct 05, 2013 10:39 pm

The 1981 Mk-7 should have the heavier yoke.

If you post some pictures it will be easier to tell which yoke you have in your Mk-7.

The danger of a thinner yoke is that they will flex and stretch a bit and let the O-ring extrude. I don't mean to downplay an extruded O-ring, but it is not a catastrophic as some people imagine... I have heard some divers thinking that the yoke will blow apart and the regulator fly and hit you on the back of the head… that is not the case.

I have seen some yokes that visibly flex when I turn the tank pressure on (even with only 2000 psi or less). I don’t use those yokes anymore. One is on a vintage Voit tank pressure checker (the angled one).

Open the tank valve very slowly and check for any visible flexing. All metals are elastic, but if you can actually see it flex it is probably the thinner earlier yoke.

What is the size of the screw on your yoke. The earlier ones used the smaller 3/8 inch screw.


Are you going to have your steel tanks tumbled?
Unless they are have obviously scales of rust and pit, they should be tumbled to truly evaluate if they have pits. The true judging criteria is the presence of pits not just rust. Rust just tends to hide pits and other imperfections, so it need to be removed.
Luis

Buceador con escafandra autónoma clásica.

73diver
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Re: Scubapro MK7 OK at 3000psi?

Sun Oct 06, 2013 1:07 pm

Hola Luis y gracias,
Soy buceador con escafandra autónoma clásica también.

Tanks: I will check with the LDS owner to see if he has tumbled the tank. It is odd. This tank was not used since 1985. It was VIP'd at that time and filled. Since 1985 the pressure had declined to about 1700psi. It is possible that the 21% air in the tank was 'consumed' to oxidize the interior but I suspect the pressure loss was due to microscopic leaks in the valve or burst disk. BTW, not to shock you, I used the tank with the air in it from 1985 for 70 minutes. I think the oxygen was at the correct level. I do have one question: This tank was manufactured for Dacor in 1973. The LDS says that the DOT exemption for the tank may have expired. I never heard of this. Could you or a fellow forum member enlighten me?

Mark VII's: I was wrong in my original post. I have one 3000psi and one that is not marked for 3000psi (pictures attached). I have asked a factory authorized repair center about 3000psi on the older one. It seems over engineered as it is.

Happy and safe diving,

Image

Image

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antique diver
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Re: Scubapro MK7 OK at 3000psi?

Sun Oct 06, 2013 5:48 pm

73diver wrote:Hola Luis y gracias,
Soy buceador con escafandra autónoma clásica también.

It is possible that the 21% air in the tank was 'consumed' to oxidize the interior but I suspect the pressure loss was due to microscopic leaks in the valve or burst disk. BTW, not to shock you, I used the tank with the air in it from 1985 for 70 minutes. I think the oxygen was at the correct level.


I do have one question: This tank was manufactured for Dacor in 1973. The LDS says that the DOT exemption for the tank may have expired. I never heard of this. Could you or a fellow forum member enlighten me?
Oxygen % in Tanks:
Yes Oxygen is consumed during the oxidation of steel, and depletion to unsafe levels may be possible. Glad you had no problems diving with it.

DOT Exemption for Steel Tanks:
Find a new dive shop!
The older I get the better I was.

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luis
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Re: Scubapro MK7 OK at 3000psi?

Sun Oct 06, 2013 10:27 pm

I am not aware of any DOT Exemption steel tanks back in 1973.

There were aluminum exemption tanks back then, but new high pressure exemption steel tanks did not show up until some decades later.

All the steel tanks that I am aware from the 70’s were DOT 3AA. The 3AA code refers to cylinders made out of chrome-molybdenum steel.

Dacor did sell some aluminum exemption tanks, but I don’t remember if it was as early as 1973 (it probably was). These were the early aluminum tanks made before the 3AL code had come out. I surely hope that your LDS can not tell the difference between a steel and aluminum tank…

If it is an aluminum tank from 1973, it would be made out of AL6351 aluminum alloy. The codes allow it to be hydroed, but it requires eddy current testing and INHO, they are not worth having them re-qualified… many dive shops will not fill them, etc…



There is probably not much risk of using the first yoke for 3000 psi, but I seriously doubt that anyone related to Scubapro will give you a go ahead to use it a pressure higher than it was originally intended for. That yoke is not over engineered and definitely not structurally over built.

As I mentioned, the biggest risk is blowing an O-ring.

Be particularly careful of any side loads on that regulator (with the smaller yoke) when mounted on a tank. If someone even tries to lift the tank by the regulator they can do some damage, but much worse if you drop the tank and hits the regulator. The yoke can easily be ruined.

The built in yokes are a bit more susceptible to minute misalignments due to bending loads. If they are not perfectly square they are much more prone to blowing an O-ring when pressurized. I have seen it happen on a Mk-7 like your (the smaller yoke) and a Dacor Olympic 800. The Olympic 800 has an even beefier yoke, but this one is just slightly bent.


Good luck
Luis

Buceador con escafandra autónoma clásica.

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antique diver
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Re: Scubapro MK7 OK at 3000psi?

Mon Oct 07, 2013 9:02 am

luis wrote:I am not aware of any DOT Exemption steel tanks back in 1973.

There were aluminum exemption tanks back then, but new high pressure exemption steel tanks did not show up until some decades later.

All the steel tanks that I am aware from the 70’s were DOT 3AA. The 3AA code refers to cylinders made out of chrome-molybdenum steel.

Dacor did sell some aluminum exemption tanks, but I don’t remember if it was as early as 1973 (it probably was). These were the early aluminum tanks made before the 3AL code had come out. I surely hope that your LDS can not tell the difference between a steel and aluminum tank…

If it is an aluminum tank from 1973, it would be made out of AL6351 aluminum alloy. The codes allow it to be hydroed, but it requires eddy current testing and INHO, they are not worth having them re-qualified… many dive shops will not fill them, etc…
All of what Luis said is why I just said "find a new dive shop"!

Also, a little extra about Dacor's early aluminum tanks... if I recall correctly, the ones with the odd-shaped thick necks did not have the exemption renewed after a certain date, and those would no longer qualify for hydro testing. I know some other similar tanks fell into that category, and I believe that also affected the Dacor ones. Sounds exactly like the dive shop is confused between steel "3AA" and "E" aluminum tanks. Do you really want them servicing your stuff? :?

It's been my experience that some dive shops want to fail steel cylinders with slight, harmless rust because they just don't understand how to make that judgement call. You may want to get a second opinion.
The older I get the better I was.

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Bronze06
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Re: Scubapro MK7 OK at 3000psi?

Wed Dec 17, 2014 7:39 am

Do any of you have what is written on the Red and Blue stickers on the MK 7 handy? Mine are pretty much non-legible.
"Where'd ya get that ol' thang, don't cha' know them thare things ill kill ya!"

Live From the Red Sea,

Russ

Diverdon
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Re: Scubapro MK7 OK at 3000psi?

Tue Feb 16, 2016 9:55 am

Image

I know its an old thread, but I have a good sticker on mine.

DD

Diverdon
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Re: Scubapro MK7 OK at 3000psi?

Wed Feb 17, 2016 10:52 pm

Red sticker:
Use audio port for primary second stage only. Use the non-audio port for added safety when attaching octopus regulator, additional low pressure hose or accessories such as utility adaptors, air moisturizers or air heaters, since these items may cause the audio alarm to not function properly if attached to the audio port.
Blue sticker:
When using the Mark VII regulator on a reserve valve, be sure the lever arm will clear the regulator when pulled, if not, the lever arm must be "DOWN" when attaching the regulator.

DD

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