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<troppo@te*.co*.au*> writes

>When I dived one, I found I was causing an open circuit effect, as the
>variable volume was insufficient for my lung capacity. 

Hmmm... find that one hard to believe, but OK, what chest size (viz-a-
viz lung capacity)
>
>I found on exhalation, I was dumping gas as the bags reached capacity, then 
>triggering the demand valve upon inhalation. The dump valve WAS set correctly.

I think you'll find that the dump valve was not set correctly (the
symptoms you describe are a classic indicator for this), but please
indicate the number of clicks from closed.
>
>Obviously, this would not happen during the average dive.

What was not average about the dive?

Chris,

My lung capacity is about 6 1/2 ltrs. I am not asking for advice how to
correctly use this thing, I was testing to see if I could use this in a high
workload, and I can't. It can not handle it. I said this would not happen on a
normal dive, where my tidal volume is I would guess <3ltrs.

Secondly, the dump valve was set to stop it going OC. It was hard to force a
dump, which is necessary to stop it going OC. On another Drager Semi closed,
the dump pressure is set at the service to EXACT pressure. It can NOT be
changed in the field.

The fact that the dump can be played with (even during the dive!) may most
times work, but is not optimal. At least not on a production unit. Several
incidents, which I do not have full details on, have occured here due the the
dump being set incorrectly by the user. Setting the dump by feel is like
setting line pressure by how the reg breaths. 

Please note I am not giving advice, nor am I qualified to use this device, (but
who really is) just making a comparison to the way the military uses these
things. The Australian Navy uses Drager Semi Closed units; they are now
switching to a MK 16 derivitive.

troppo

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