| Once again,
with the approach of winter, it is rebreather building season. The BQ-50
went a fair bit beyond its budget of £50, breathed like a pig and
leaked. It was intended as an oxygen rebreather for decompression use in
remote places to maximise gas use. It worked, even seeing use on a dive
in Loch Ness, but the hassle of using it outweighed the inconvenience of
carrying lots of oxygen to remote places.
Problems:
-
Polyplumb parts
are convenient, quick to build and watertight. However they are big and
awkward, expensive and look awful
-
The DSV, made from
a Polyplumb T-section, was too small a bore and the mouthpiece was uncomfortable.
The shut-off valve put too much dead space into it and held the DSV in
a weird position.
-
The scrubber was
made from a rocket tube. Very good watertight properties, almost indestructible
but just far too big. The "there and back" arrangement added to the work
of breathing problems because the lid could not be drilled because of the
rotating inner section. The inhale and exhale connections were both in
the bottom.
-
The counter-lungs
leaked. Bin bags and duct tape are not good construction materials.
-
The hoses were
too small. I used a 25mm flexible duct pipe, excellent crush resistance
and smoot bored but just too small. I never knew any better!
The BQ-100 was
a disaster. The idea was to take the BQ-50 and turn it into a semi-closed
rebreather. My idea was to have the counter-lungs sized just a little smaller
than my lung volume. This would mean that when I took a breath, the lungs
would bottom out and a standard 2nd stage regulator would make up the shortfall.
When exhaling, the loop would be overloaded and the excess would be dumped
offboard. This would insure a constant replacement of gas with each breath,
sounding remarkably like the operation of a certain other rebreather. At
least in theory. It all fell down in practice: it worked as long as you
were taking a full breath and were very deliberate about how you breathed.
If you let your breathing pattern relax to a more normal pattern, or started
taking short and fast breaths, then the system would no longer inject gas
because the lungs were not bottoming out. Luckily, I never even took this
near the water and the whole idea has been abandoned. I am not a fan of
the "dump & replace" system tied to lung volume. It just seems very
fragile system.
And so the BQX
is now in construction. More |
System
outline
Development
Diary:
26th
Oct 2003
To Do
Suppliers |