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Master Diver
Posts: 447
Joined: Tue Jul 18, 2006 10:26 pm

109 Balanced vs. Unbalanced

Sat Aug 13, 2016 9:59 am

Occasionally I get questions about the advantages and disadvantages of balanced vs. unbalanced second stages. I thought I would post a few comments here not just because I'm lazy and pointing to a thread is easy, but also to open the discussion for other's insights.

When a second stage is mated with a balanced first stage such as a MK 5/6/7/8/9/10 it will make very little difference in performance with either a balanced or unbalanced second stage. Performance-wise, the advantage of a balanced second stage is realized when it is mated with an unbalanced first stage. (MK 2/3/200) The balanced second can compensate somewhat for the lower IP an unbalanced first stage will deliver at lower tank pressures.

Performance aside, here are some of the pluses and minuses of each.
Balanced second stage
Holds tune longer.
Can accommodate a wider variety of intermediate pressures.
The seat last longer (due to a lighter spring pressure when not in use.)

Unbalanced second stage
Seats are less expensive and can be flipped over and used on both sides.
Fewer o-rings makes for a (marginally) cheaper service.

I'm sure there are other ideas out there; let's hear them.

BTW Service kits for balanced and unbalanced 109s are available from VDH
A sincere THANK YOU to all at VDH who make this wonderful resource available and to all the thoughtful contributors.

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Plank Owner
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Joined: Fri Jun 24, 2005 11:40 am
First Name: Bryan
Location: Wesley Chapel Florida
Contact: Website

Re: 109 Balanced vs. Unbalanced

Sat Aug 13, 2016 10:34 am

Great post Coonass! This is the kinda information we need.

I know for years it was up to the resourceful DIY diver to fabricate parts they could no longer get or to re-use parts out of thriftiness. But when youall are servicing your gear please don't forget about me. Seats and O-rings are cheap in the VDH store but every $$$$ counts in the small business world and 75% of it goes towards bringing back more parts for our gear :D

BTW, New volcano orifices for 109's in chrome plated brass are in production now along with correct size chrome plated phillips head screws for the rings!! ETA around the 1st of September.
Doing it right should include some common sense, not just blindly following specs and instructions. .Gary D, AWAP on SB

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VDH Moderator
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Joined: Sat Jun 25, 2005 1:53 pm
First Name: James
Location: Kansas

Re: 109 Balanced vs. Unbalanced

Sat Aug 13, 2016 11:12 am

The only regulator that causes as much drooling, maybe, as an Argonaut is the lovely R109. Lovely to look at and lovely to dive.

Couv got ahold of my set back aways just for a go over to satisfy me I had them working correctly (not being a SP expert at all). I have to say, they are awfully smooth and they are running mostly VDH parts including the Conversion Kit to Balanced.

One can repair a Conshelf second stage with a hammer, the 109 needs a little finesse I think.


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