kworkman
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MK2 and 3

Thu Jun 09, 2016 12:53 am

The MK2 and 3 are nice for the size and simplicity and ease of rebuild. I dont much like the fact that they are unbalanced and the IP drop seems to be 20psi or so. I rebuilt an MK3 tonight and it had one shim. IP locked in at 132 at 2500psi tank pressure. At 300psi tank pressure it was 108. How does low IP affect performance, assuming Im conected to a balanced 2nd stage?

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Bryan
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Re: MK2 and 3

Thu Jun 09, 2016 6:13 am

If you are going to work on as wide a variety of regulators as you do then this should be one of the most used tools you have.

http://www.scubatools.com/p-603-regulat ... bound.aspx

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Doing it right should include some common sense, not just blindly following specs and instructions. .Gary D, AWAP on SB

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Herman
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Re: MK2 and 3

Thu Jun 09, 2016 6:43 am

The answer to your question is , it doesn't.
What you have to understand is what the purpose of balancing is and it's not what most think. It is not to keep the IP constant but rather to keep the cracking pressure and breathing resistance of the second stage constant as tank pressure changes. There are 2 ways to do this, balance the first stage which keeps the IP constant which in turn keeps cracking pressure constant OR balance the second stage which will keep the cracking pressure constant reguardless of IP (within reason). While most all manf pair a balanced first and second, there is really no need since balancing either will accomplish the task, balancing both does not hurt anything but is redundant and accomplishes nothing....except a higher sales price. So if you put a balanced second stage on an unbalanced first or vise versa the result is the same, the cracking pressure of the second stage does not change as tank pressure changes, which is to goal of balancing either stage.
Herman

kworkman
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First Name: Keith
Location: Columbus, OH

Re: MK2 and 3

Thu Jun 09, 2016 7:55 am

Ok that makes sense. I may have come across that before but not as clearly stated. Ive got the Vance Harlow book but I do need to pick up Peters book.

swimjim
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Re: MK2 and 3

Thu Jun 09, 2016 5:32 pm

kworkman wrote:Ok that makes sense. I may have come across that before but not as clearly stated. Ive got the Vance Harlow book but I do need to pick up Peters book.
Good idea. I own both books myself and refer to both when I am working on projects where I am out of my normal element.

Jim

jconley
Skin Diver
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First Name: Jeff
Location: Apex NC

Re: MK2 and 3

Mon Jul 18, 2016 3:46 pm

MK2 / MK3 question
I have heard people say that the MK2 doesn't deliver enough volume of air to support 2 - 2nd stages at deeper depths (say 100'). Any truth to that? Since there are rumors about the MK2. What about the MK3 since it has a smaller piston? Opinions?

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Bryan
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Re: MK2 and 3

Mon Jul 18, 2016 5:37 pm

I remember a test, I think it was in Japan or somewhere in the far east where they hooked dozens of 2nd stages up to a MK2 in a pool with divers breathing off of all of them. Could not find a link or more info on it though......

On a somewhat related note.....I had someone call me today asking about servicing a MK6........One of the shops here in Tampa told him they were banned years ago because the pneumatic yoke exploded and would hit you in the back of the head.
Doing it right should include some common sense, not just blindly following specs and instructions. .Gary D, AWAP on SB

jconley
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Location: Apex NC

Re: MK2 and 3

Tue Jul 19, 2016 2:40 pm

Bryan wrote:I remember a test, I think it was in Japan or somewhere in the far east where they hooked dozens of 2nd stages up to a MK2 in a pool with divers breathing off of all of them. Could not find a link or more info on it though......

On a somewhat related note.....I had someone call me today asking about servicing a MK6........One of the shops here in Tampa told him they were banned years ago because the pneumatic yoke exploded and would hit you in the back of the head.

I remember hearing that rumor about the pneumatic yoke, when I worked in a Scubapro dive shop. As far as I know the exploding was just one of the many rumors about Scubapro equipment. Maybe started by competitors. Or maybe the source was the rumor I heard below.

The other rumor I heard was if something struck the regulator while you were underwater it would break the seal with the o-ring on the tank valve. I only saw a few of the pneumatic yokes. What I remember about them, was sometimes they were hard to get to seat against the tank valve o-ring. Maybe that was source of the dislodging rumor. I assume that was the reason Scubapro stopped making them.

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couv
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Re: MK2 and 3 and MK VI

Tue Jul 19, 2016 8:01 pm

Pardon my cut and paste from that other diving board.
http://www.scubaboard.com/community/thr ... ge.454171/

I worked in a dive shop in the 80ies, and we had a couple MK VI regs in the rental/student fleet. I remember it being used in pool classes, but no one seemed to trust it for open water.

The pneumatic yoke seemed like a good idea, but it turned out to be more difficult to properly seat than a common screw on yoke.

As far as exploding; I converted my MK VI to tank pressure check/tire fill duty. I've had it on my 3442 tank with no problems other than having to readjust the yoke to fit over a larger valve.....sort of defeats the purpose of having a pneumatic self seating yoke.

But, I did an experiment to test the security of the pneumatic yoke: If the pneumatic yoke is properly adjusted, it will pressurize and seat with less than 100 psi. However, even if properly adjusted a bump or a sideways tug on the first stage can cause unseating at 400 psi and a leak at 750 psi.

The thread linked above has some interesting comments posted by Sam Miller et al.
A sincere THANK YOU to all at VDH who make this wonderful resource available and to all the thoughtful contributors.

jconley
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Re: MK2 and 3

Wed Jul 20, 2016 4:42 pm

Thanks couv,
Your comments here and link you provided. Puts, the rumors to a close in my mind.

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