Is the plastic MAV meant to be not very good...?

lizardland

... or have I got a duff one?

I've just got a new plastic MAV, fitted it and did my first dive on it today.

Two main things:

- are the hose connections supposed to be so easy to undo? I'm talking about the screwed part, not the Swagelok fitting. Mine seem to undo with a bit of effort by hand and I don't especially want to start torquing them up into the plastic body.

- is the O2 flow on the bypass supposed to be so low? On the old stainless model if you pushed the button you could get a good lungful of O2 for flushing. This one seems to do a rather feeble hiss of oxygen, I have to push and wait on this one. Rather worryingly, it was a bit hard to either hear or feel if gas was flowing when I was pushing the button, it was push-wait-check display-push-wait-check display. There's no way I'd want to be using this on a scootering dive.

If this is how it's supposed to perform then I'm not overly impressed, really seems like a step backwards from the old stainless models, I'll probably stick the plastic MAV on my homebuild and go back to the stainless lump. Just wanted to check what other people's experiences were.

Cheers,

Stuart

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Dutchy

It takes a few seconds indeed to fill a lung. I've never known otherwise. The only place where I really notice this is @6 doing a full flush to check the displays. So yeah that takes a while.
I'm happy with it although it doesn't double as a hammer like the hydrogom and old style valves do
On a serious note I guess it doesn't feel like you are used to so it isn't ok. But isn't it? How much do you want it to deliver? Worst case you go up uncontrollably. I did and had a fine pPO2 on the surface.
With respect to tightening. There are explicit instructions in the manual. Something alomng the lines of 'two fingers' if I remember well...

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Mike Costanzo

I've noticed that too but the more I dive the plastic MAV the more I am getting use to the amount of time I need to push the button to deliver the O2 required to maintain my target PO2.

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Mike Costanzo
CK #318

Marky Mark

I've only ever used the plastic version (CK273) and I find it takes a good push before I hear the gas going in. I have had the connections loosen just by moving the hoses into place, seems wrong, but I've never had a leak, I'm a little more careful these days. I suppose steel into plastic won't tighten up like steel into steel.

MyM

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cys

I would try rebuilding it. The O2 flow on the bypass should be considerable...

lizardland

That's what happens on mine, flex the hoses and it makes the connection twist. Mine didn't leak either but I am a bit concerned on the longevity of the body before it starts to wear.

I'm used to being able to do what is effectively open loop on O2. There are times when I'd like to push the button and inhale pure O2 rather than wait for the loop volume to come up. The old MAV pretty much filled your lungs with O2 when you did a big button press or you could get a very slow squirt if you used less pressure. It all just seems a bit vague and lacking any positive feedback that something has happened without looking at the displays.

I'm really not impressed with it, I'll give it a few more dives but my gut feeling is that the old valve is going to go back on.

__________________
Can you imagine drifting along in the sea with your mouth open and a load of f***ing plankton going in? You'd like it, would you?

www.westons-cider.co.uk

Azerbaijani Association of Technical Divers Publicity Officer and Goat Wrangler

Dutchy

I've tried that in the past and it only works when I'm really really calm (so not when you'd need it). Based on your remark I'd say you're valve is normal, you just like the other kind of 'normal' better.

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jradomski

I remember talking to Gordon when he was first working on the injected molded MAVs, one of the goals was to reduce the flow so that the there was better control by the diver.. I know there will be a manual dil addtion valve available soon, that will have flow increased..

Personally, I think the positives of a reduced O2 flow outweigh the negatives...

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CCR Trimix Instructor Trainer
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All posts are personal opinions and DO NOT reflect any affiliated agency unless specifically stated.

lizardland

I'm not convinced. With the old stainless valve I could get anything from a slow trickle to a lung-stretching blast, depending on how you press the bypass button. I may be over cautious but I like being able to suck a big lump of oxygen in quickly if I've tripped the ADV near the surface with a hypoxic dil as well. Maybe I'm just not used to it but I felt a bit like I was having to think one step ahead. The plastic valve body just doesn't feel particularly resilient either and you've lost the ability to survive a HP seat failure.

For me, the orifice is for reduced flow, the bypass should be exactly that, a bypass not a faster trickle.

Anyone know what the bypass flowrate on the Hydrogom is like?

Cheers,

Stuart

__________________
Can you imagine drifting along in the sea with your mouth open and a load of f***ing plankton going in? You'd like it, would you?

www.westons-cider.co.uk

Azerbaijani Association of Technical Divers Publicity Officer and Goat Wrangler

RobPot

What was wrong with the old valve?
Haven't had any problems with ours and haven't considered replacing it.

Robert.