Inspration Modification

The Inspiration stands as the current state of the art in a mass-market electronic CCR. I recently had the opportunity to have one come across the bench here and I spent many hours studying it. I've got mixed emotions about it: One one hand, it's very neatly integrated, and very "factory made" in every way. On the other hand, the construction is really pretty lightweight and I'd question it's long-term durability in extreme condition use. Then there's that issue with divers dying on them, which cause is yet to be established. One theory is that the divers involved were all just dumb-shits. That's actually probably a pretty good theory and the one that I presently believe is most likely. There's a second, more technical theory also. That theory runs towards the following: There is a potential in any rebreather for a thin film of water to block the faces of the sensors. Don't think of this as liquid water, think of it as the thin film of a soap-bubble. If this occurs, the gas trapped behind the sensor will be that of the loop gas at the moment the sensor "bridges". As loop PP02 drops, the sensors don't see the now too-lean gas, and the system fails to inject 02. This has been demonstrated on the CIS Lunar rebreather, which has data-logging capability. The CIS also has a way to blow a small stream of gas at the sensor faces in order to both validate their response, and to clear away the vapor if needed. I was talking to a few other rebreather divers aboard the R.V. Seeker one nice afternoon this autumn, and I mentioned this, and mentioned that I bet I could make a similar system for the Inspiration. Well, to make a long story short, a couple of divers presented themselves soon after at my doorstep, bearing an Inspiration, and saying "Prove it". So, without further delay, I got to work and made up "Diver Dave's Inspiration Diluent Puffer System".

The goal was to make a 3-port nozzle that would allow a controlled puff of diluent to be blown towards the 3 sensors. I made this little nozzle out of a bit of white delrin, bonded to a short length of stainless steel tubing.

The center spool of the sensor bay is a plastic that's virtually impossible to glue anything to, so I made a small threaded brass port that was inserted into a hole, drilled and tapped to accept it.

Here is the brass port looking from the inside of the spool.

With the brass port in place, the stainless steel tubing was passed into the center of the spool, and a bit of epoxy adhesive was used to bond the stainless tubing to the brass port.

And here's the result: A carefully placed nozzle, with 3 small orifices pointing towards the three sensors.

Now we need to supply diluent to the port. I decided to use normal BC connection parts to bring gas into the scrubber, and made the little brass adapter that will accept a bit of Tygon tubing which will be used to carry gas to the nozzle assembly. This brass part is threaded into a modified BC inflator stub.

Here's the internal placement of the brass tube adapter.

And here we can see a bit of Tygon tubing has been installed.

Looking from the outside of the scrubber can, we see the newly installed BC inflator stub at the 8 O-Clock position, and the nozzle assembly in the center of the spool.

The other end of the Tygon tube is attached to the stainless-steel tube feeding the nozzle, and clamped with a stainless-steel ear-clamp. Things get pretty tight in there, as you can see. No room for errors in geometry of the parts.

My finger is pointing at the inlet for the gas. I routed the Tygon tube parallel to the internal wiring to the sensors, so the entire assembly can be serviced for sensor-changes without the need to disconnect any additional components.

Here's a view with my hand out of the way. Remember, this is a high-resolution photo. You can save it to your hard drive and then enlarge it using any photo-editing software to get a very detailed view.

The last step was making up a feed system to allow the diver to "feather" a shot of gas into the system. I elected to modify a BC inflator for this purpose.

Essentially, I hacked off the mouthpiece section, chucked it in the lathe, faced off the stub, and then epoxy bonded a Delrin spool to the interior of the old inflator. I ported it so that the gas that is injected into the body passes back through the newly installed brass barb fitting.

Then a new hose was attached with a BC quick-disconnect to take that gas back to the rig. The inlet to this valve comes from the diluent feed block inside the chassis.

The end result is a system that allows the diver to verify sensor integrity at any time, and to clear a blocked sensor should a stagnant PP02 condition be found.

That's it for this project. It seems to work well, and I must say that the mechanical part of the conversion came out pretty well. Feel free to copy it. It took me about 20 hours to think up, and about 5 hours to perform. It seems an incremental improvement, but one that may offer some additional confidence in the system.

		The goal was to make a 3-port nozzle that would allow a controlled puff of diluent to be blown towards the 3 sensors. I made this little nozzle out of a bit of white delrin, bonded to a short length of stainless steel tubing.
		The center spool of the sensor bay is a plastic that's virtually impossible to glue anything to, so I made a small threaded brass port that was inserted into a hole, drilled and tapped to accept it.
		Here is the brass port looking from the inside of the spool.
		With the brass port in place, the stainless steel tubing was passed into the center of the spool, and a bit of epoxy adhesive was used to bond the stainless tubing to the brass port.
		And here's the result: A carefully placed nozzle, with 3 small orifices pointing towards the three sensors.
		Now we need to supply diluent to the port. I decided to use normal BC connection parts to bring gas into the scrubber, and made the little brass adapter that will accept a bit of Tygon tubing which will be used to carry gas to the nozzle assembly. This brass part is threaded into a modified BC inflator stub.
		Here's the internal placement of the brass tube adapter.
		And here we can see a bit of Tygon tubing has been installed.
		Looking from the outside of the scrubber can, we see the newly installed BC inflator stub at the 8 O-Clock position, and the nozzle assembly in the center of the spool.
		The other end of the Tygon tube is attached to the stainless-steel tube feeding the nozzle, and clamped with a stainless-steel ear-clamp. Things get pretty tight in there, as you can see. No room for errors in geometry of the parts.
		My finger is pointing at the inlet for the gas. I routed the Tygon tube parallel to the internal wiring to the sensors, so the entire assembly can be serviced for sensor-changes without the need to disconnect any additional components.
		Here's a view with my hand out of the way. Remember, this is a high-resolution photo. You can save it to your hard drive and then enlarge it using any photo-editing software to get a very detailed view.
		The last step was making up a feed system to allow the diver to "feather" a shot of gas into the system. I elected to modify a BC inflator for this purpose.
		Essentially, I hacked off the mouthpiece section, chucked it in the lathe, faced off the stub, and then epoxy bonded a Delrin spool to the interior of the old inflator. I ported it so that the gas that is injected into the body passes back through the newly installed brass barb fitting.
		Then a new hose was attached with a BC quick-disconnect to take that gas back to the rig. The inlet to this valve comes from the diluent feed block inside the chassis. The end result is a system that allows the diver to verify sensor integrity at any time, and to clear a blocked sensor should a stagnant PP02 condition be found.