DangerBoy
New Member
Posts: 3
Joined: Wed Mar 29, 2017 12:31 am
First Name: Roger
Location: Calgary Canada

ScubaPro Mk VII Advice needed

Wed Mar 29, 2017 12:25 pm

Hello everyone,

This is my first post on DoubleHose. I have a lot of old diving equipment from the 70s that I still want to use. In the collection is a 1st generation Scubapro Mark VII regulator that I plan to service and get working again. I know that the later generation Mark VII regs had heavier yokes for higher pressure tanks but I'm wondering if anyone has used the first generation Mark VII units with the lightest rated yokes on 3000 psi or 3300 psi rated tanks. The new (used) tank I just bought is a 100 cu ft 3,300 psi AL tank and I would like to use my old Mk VII reg on it. I'm an engineer and I know things are usually designed with a fairly healthy factor of safety built in so I have a hard time believing that the reg will fly apart as soon as I crack the valve and put 3,300 psi into the reg but I'd like to know if anyone's successfully used one of those 1st Gen Mark VIIs on a 3,300 psi tank or knows of instances where the yokes on these regs have failed at higher pressures. (P.S. Don't worry about getting sued for responding to this question or offering an opinion: I'm Canadian and we haven't yet made a national sport out of suing everyone for every possible thing. :wink: )

Another issue I have is that the BC I've always used is also from the 70s and is strictly manual inflate with no provision for direct/tank inflate. Because of that, the Mark VII does not have an accessory LP hose for inflating a BCD, nor does it have a back-up/secondary second stage. I don't have the reg with me right now but I understand there is a second LP port I can tap into for that. My question is, do I need a special Scubapro splitter to tap into that port and run additional hoses off or can I just use a generic fitting for that? If a generic fitting will do, is there a specific thread size I need for that port? I don't know a lot about regulators so I'm not sure if port sizes and thread pitches are standardized or brand specific.

Thanks for your help.

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luis
VDH Moderator
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Joined: Thu Jun 30, 2005 9:28 pm
First Name: Luis
Location: Maine

Re: ScubaPro Mk VII Advice needed

Wed Mar 29, 2017 10:00 pm

Welcome to the board.

The potential or typical mode of failure for a vintage undersized yoke, when it is used with higher pressures than intended, is not a catastrophic structural failure. It is more of a small elastic flexing of the yoke that allows the O-ring extrusion and blown O-ring. The yoke flexing is often not visually evident, but the blown O-ring does not go unnoticed. This doesn’t happen often, but it can. As you said, there is a safety factor.

Pre-tightening the screw yoke can sometimes prevent the blown O-ring, but it is not a great solution.

I think there were actually 3 different yoke sizes for the Mk-7, but I never tried any of them with a 3000 psi cylinder.


All LP ports on most regulators (Poseidon is the only exception of well know regulators) are 3/8”-24 standard ports.

As far as I remember, the Mk-7 has two LP ports, one will actuate the sonic reserve and the other one will not. You can put any kind of LP splitter adapter on either one if it doesn’t present an interference with another hose.

Good luck
Luis

Buceador con escafandra autónoma clásica.

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couv
Master Diver
Posts: 409
Joined: Tue Jul 18, 2006 10:26 pm

Re: ScubaPro Mk VII Advice needed

Thu Mar 30, 2017 8:33 pm

Welcome to the board Danger Boy,

I've not connected a MK7 to my 3442 tank, but I did hook up a MK5 with a thin yoke, and just as Luis said (you'll soon find out he's always right) the yoke can stretch causing a blown tank valve seal. A fresh o-ring and a bit more torque seem to do the trick.

I thought I had a genuine SP MK 7 low pressure splitter but it turns out to have SAS stamped on it. Anyway, if you're interested in it $5 plus shipping and it's yours.

BTW you will find Bronze06's project helpful. He just did video on rebuilding the Honker and has thrown in some interesting tidbits.
viewtopic.php?f=17&t=9145

Addtionally, scroll to the bottom of any page on this site and click on MANUALS AND CATALOGS then find your way to the ScubaPro folder and download the annotated copy of the MK 7 parts diagram. It has all the o-ring sizes listed on it.
A sincere THANK YOU to all at VDH who make this wonderful resource available and to all the thoughtful contributors.

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Bronze06
Master Diver
Posts: 663
Joined: Tue Jul 01, 2014 5:33 am
First Name: Russell
Location: Tabuk, Saudi Arabia

Re: ScubaPro Mk VII Advice needed

Sat Apr 01, 2017 5:19 am

Re-did all three videos with the correct procedures. Sorry folks about the first screw ups. Lesson learned is never attempt to do re-build videos while tired. Follow all procedures as per the given regulator type FROM THE REPAIR GUIDE. Check and re-check. Thanks to the above guys for squaring me away.

https://www.youtube.com/watch?v=plyZb09K8Zk&t=17s video 1

https://www.youtube.com/watch?v=zUWv1QRAS8w&t=7s video 2


https://www.youtube.com/watch?v=ANOwf7tHSXs video 3
"Where'd ya get that ol' thang, don't cha' know them thare things ill kill ya!"

Live From the Red Sea,

Russ

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