Manifolds on Twins: It's an open and shut case

[Mark Chase]

Originally Posted by Digger

Bob, I've wondered this for a while. A lot of people have told me to do this throughout my training "all the way open and back half a turn" but recently I heard from a mate who I usually turn to for reasonably good advice that it wasn't necessary with balanced valves, and it's just a legacy from the old vertical pillar valves which could stick open if left all the way open.

I can see that you don't want to jam the thing open when you do it, but up to the stop should be ok shouldn't it?

Just wanted to get it straight, thanks in advance.

Digs.

DIR do not use balanced manifolds.

ATB

Mark Chase

[Bob Cooper]

Originally Posted by Digger

I can see that you don't want to jam the thing open when you do it, but up to the stop should be ok shouldn't it?

Having the valve open all the way up to the stop will effectively squash the stem o-ring between the stem and the bottom of the packing nut. Imagine opening the valve all the way to the stop and then filling the tank like this. The additional force on the stem o-ring, combined with the tank pressure will really give that o-ring a hard time. Repeatedly doing this can shorten the life of that o-ring.

It's the same with all valves, whether they are radiator valves, the stop cock under your sink or the bathroom tap. It's just good engineering practice not to force the stem up against the packing nut.

[Bob Cooper]

Originally Posted by Mark Chase

DIR do not use balanced manifolds.

Really? Why's that then?

[Captain Jack Sparrow]

Half a twist for me! And big rubber knobs make shut downs simple

[Mark Chase]

Originally Posted by Bob Cooper

Really? Why's that then?

The balanced manifold has face 0 rings and DIR don’t like face 0 rings they use the Scuberpro or Halcyon (which is a S-pro copy) with enclosed 0 rings and these are not balanced manifolds. I know I have one and its crap. My MDE manifolds can be turned on and off wit just my finger tips. My Scuberpro one is a bugger when the tanks are charged up.

Apparently there is a way to modify the valves to improve the free movement bit I don’t know what that is and it’s besides the point the Halcyon and S-pros are not balanced manifolds.


ATB

Mark Chase

[beanie]

Originally Posted by Mark Chase

The balanced manifold has face 0 rings and DIR don’t like face 0 rings they use the Scuberpro or Halcyon (which is a S-pro copy) with enclosed 0 rings and these are not balanced manifolds. I know I have one and its crap. My MDE manifolds can be turned on and off wit just my finger tips. My Scuberpro one is a bugger when the tanks are charged up.

Apparently there is a way to modify the valves to improve the free movement bit I don’t know what that is and it’s besides the point the Halcyon and S-pros are not balanced manifolds.


ATB

Mark Chase

my scubapro manifold is balanced

[Mark Chase]

Originally Posted by beanie

my scubapro manifold is balanced

Interesting I didnt know scuberpro made a balanced manifold I thaught it was just SOS and MDE

Its not the same as my Scubapro one. Does it have face O rings?

ATB

Mark Chase


EDIT

My mistake I was thinking of Bever not Scuberpro. My manifold is a Beever Its MDE and Scuberpro that make balanced manifolds. I have an unconfirmed tip that the DIR boys mod their manifolds to make them ballanced by cutting a slot in the widget. But this is a not DIR srced tip so may be bollox

[Bob Cooper]

Originally Posted by Mark Chase

The balanced manifold has face 0 rings and DIR don’t like face 0 rings they use the Scuberpro or Halcyon (which is a S-pro copy) with enclosed 0 rings and these are not balanced manifolds. I know I have one and its crap. My MDE manifolds can be turned on and off wit just my finger tips. My Scuberpro one is a bugger when the tanks are charged up.

Sorry Mark but this is all a load of bollox.........

First, there's no such thing as a balanced manifold. The valves may be balanced by equalising the pressure across the seat assembly and I imagine that is what you are referring to.

Second, it's quite wrong to say that "a balanced manifold has face o-rings" This statement has no meaning and is misleading. Some manifolds (MDE, OMS etc) rely on a facing seal, others (Halcyon, Scubapro etc. rely on a barrel seal). This has nothing to do with them being "balanced" or "unbalanced".

Third, the Halcyon manifold isn't a copy of the Scubapro. Far from it.

Fourth, the Scubapro and Halcyon manifolds use balanced valves. If your s'pro is giving you trouble give it to me, I know how to fix these things ;-)

Sorry to be mister picky but people on here might read your stuff about manifolds and actually believe it.

[Woz]

And here is my ten pennorth just to get my reputation thingy hacked to death.

I dive twin 7's (and they are not a ladies set, thank you Digs) 'cos I'm a bimbler rather than a dark deepie. I had a nice long sit down and looked at a failure at various points during a dive. And came up with...... WozDowns.

At reasonable depth (say 30m) there is not enough gas in twin 7's to shutdown safely with a pressure of less than 100 bar. So I dive the isolator open 1/2 a turn until I get to 100 bar. Then close the isolator and continue breathing off my right pillar until I hit 50 bar. Then swap to reg on left pillar. This way, I have minimal task loading (only one knob turn and one reg swap), no silly open and shutting all the time and I'll always have enough gas to get me to the surface. Sort of a halfway house between indies and a manifolded set. Oh- and I also run an SPG off each pillar so I can tell when checking contents that the manifold is open enough and the cylinders are equalising properly on the way down to 100 bar.

And on the great balanced/unbalanced debate, I use an Agir Brokk manifold and rubber knobs which has the lovely barrelly O ring seals and balanced valves. MDE manifolds are, however, beautifully made and finished and if they made a manifold with barrel seals rather than face seals they would absolutely clean up the market. I know the ex technical manager of MDE and he tried to persuade them not to use face seals but ho hum, they ignored him.

[Finless]

Do you know, I had never even thought of closing and opening the manifold during a dive (is that a cave diving technique?). I mean, you might as well dive indies BUT then again ...... all remaining gas still available ........

Isn't repeatedly playing with your knob increasing the chance of a failure during the dive? Good shut down practice, though.

I'll stick with "open a little" bit throughout the dive - I haven't died thus far.