breathing effort/ DSV

MatV

I am just desintegrating my Inspi to give the loop some TLC.
It is the first time I do this.
As I was taking apart the DSV, I was struck by what I think is a very poor and cheap design.
The DSVs inner bore is 38 mm, and the checkvalves have just 26,7. The checkvalves are just plugged into the big bore, leaving the cross diamate mismatch as it is. They are sharp edged and a bad mold. Phew :-(.

I put it to the machine, CL hoses attached, and measured an exhale pressure of more than minimum 4, slight effort laden 8 mbar. My Poseidon regs show 3-4 maximum, 1,5mbar minimum.

In a time given, I was able to ventilate twice as much volume (medical volumeter) using the Draeger dolphin hoses, than with the Inspi. And that is only part of the loop.

Now the Draeger Checkvalves sit in a 38,5 mm bore and move like Eiderdown.
Have lathe, will sacrilege.

Why do people claim, that the Inspi breathes easier than a good OC reg?
Are they mislead by the fact that the inhale CL will feed them because of the hydrostatic pressure gradient in a normal position? Is this the reason why on pics Inspi divers seem so badly balanced in an upright position?

I hope to get soon over this. Otherwise there is 22nd November.

Matthias

rewrites

Hi Matthias

Interesting point. However, the DSV and hoses are only part of the overall loop - and hence only one part of the whole system when comparing perceived or measured WOB.

Although the DSV is poor compared to your Draeger hoses, that's not to say the rest of the loop in the Inspiration does not out-perform the Draeger - or any other Rebreather for that matter - thus producing an overall WOB that is similar or better.

Would be interesting to have a breakdown of individual components's and their efficiency in the loop. Would be then possible to identify weak components and how the unit works as a sum of its parts. I would imagine the manufacturers are well on top of this and trying to optimise where financially and mechanically possible.

PH

Simon A

Matthias,
If your inspo check valves are 26.7mm diameter then you should ring up AP and order some more. The current check valves are 31.2mm diameter and look much closer to the draeger check valves (they also breate a lot easier) I have an old one here with the 26.7mm measurement, but every set I've ordered in the last 3 years are the new style.
HTH
Simon A

MatV

Simon,
Thanks, that helps a lot. Next stop is, fixing tha "missing Sensor II" problem.
Sensor is showing 12.3 mV output on air, so it is probably the Molex connector. I am very suspicious of the black centering piece. This could very well center the jack w/o making contakt to the pinholes. Will try to put some bias on the pins. Then lubricate every joint with "Wetprotect nautic".

Then isolate the cable glands leading throught the top from cold by some foam or delrin half-caps, to minimize inner condensation.

Matthias

MatV

While they are only one part, they are probably the most critical, since speed of gas travel slows down once in the exhale lung.
Still, all respiratory resistances are line up in series. This makes me look for the weakest parts first.

Others are the t-piece(s) which are not deburred, at least in my rig, and the squeezing situation of the hoses at the shell's cutouts.

Often hoses get deformed here, increasing WOB. Calls for cooper hoses.

Ideal would be, cooper hoses all around, T-joints which may turn in their counterlung joint, a dolphin DSV ( or a Submatix or Tecme Bailout-DSV), and a soft bend at the scrubber entry ( causes lots of WOB, as opposed to a bigger radius one... ) No free lunch, obviously.

Matthias

rewrites

agree with you on this point. I have enlarged the casing cut-out on my unit to avoid this very situation as I found the hose crushed by as much as 30-40%

Peter

Simon A

It's unlikely to be the black plastic locking piece. It could be the molex pins have tarnished and gone black. Taking the connectors out of the molex plug and cleaning them, and cleaning the pins on the cell may work.
But I bet you that the wire that goes into the molex connector is black and has snapped just where it connects to the pin. If there's enough wire you want to cut back beyond the blackened bit and crimp new molex connectors on.
If you want to spend a lot of time it is possible to (carefully) scrape the potted conection box out, replace the wires to the cells with marine grade tinned wire and crimp new connectors on (remember to repot the box once you've tested it).

HTH
Simon A

MatV

It was something in between. The sensors pins were easily cleaned with a spliced cotton swab, and the plug with a tooth pick. I did not dare unveiling the crimped cable from the molex shell, because I have no real ideal which tools I may need to dig it out or put it back. Any info welcome. The cables seemed ok to me, but the one molex receptacle was clearly somewhat bent, so that the acording pin did not match it, and this was aggravated by the black center ring, which kept state. I found when I insert the first portion of the pins into the jack with some tilt, it then centers and makes positive contact and sits reasonably tight. In the wrong position it has idle play.
Seems this is ok now. Two sensors show .22 before calibration, one .17. Will the calibration process take care of that for a reasonable time, or should I replace it? (Date of sensors unknown)

Regards,
Matthias

Simon A

Mathias,
First I'm going to recommend that you take training on the unit, a CCR is an easy way to kill yourself if you don't understand it and monitor it constantly.

Once you start calibration the inspo will tell you if it can calibrate with the cell, as long as the cell health is good it will calibrate and sort this out.

When cells age they either fail completely, or they get current limited. The upshot of this is that a cell that passes calibration (even a brand new cell) can be unsafe to dive.

As to replacing the cells, what is the date code on them? If they are teledynes there should be a serial no and a 2 digit alphanumeric code on each cell, the letter is the month (A=January, L=December) and the number is the year (1=2001, 8=2008). eg - E5 is May 2005.
If the cells are less than 12 months old and calibrate I'd use them for the course (you are going to have some form of instruction?) and carry 1 spare cell.
If the cells are less than 18 months old and calibrate I'd use them, but carry 3 spare cells.
If the cells are less than 2 years old and calibrate, I would use them for couch diving to test the unit (you need someone to watch you whilst you do this) and maybe at 0.7 setpoint to test in a pool (after testing on a couch dive), but I would not dive them in open water.
If the cells are greater than 2 years old and calibrate I may use them to couch dive the unit for testing, (remember someone needs to watch you do this, and remove the dsv from your mouth if they think there is a problem) but I wouldn't use them in the water.

HTH
Simon A

MatV

Hi Simon,

Thx for your sensor management advice.
I was thinking if "pulling up" a sensor which shows lesser voltage but is otherwise ok would put some stress to the circuit which might reduce reliability.
My rig, which I had bought 2nd hand, showed some faults at an early training stage, which made me postpone the completion of my training until I have sorted out some problems. At the same time I take try to sort out some issues which seem design errors to me. Not all, by no chance. And I try to gather data which revisions have been made till today on it.

-Fix neg. pressure test problem ( no design error..)
-Sensor contact problems , may be I'll change to the new center pin ones
-WOB, fix the checkvalve issue, later go for better hoses, and better t-joint, hope I can make it turn to avoid kink, same goes for DSV, inner diameter of hose glands
-Bailout DSV
-Isolate solenoid to avoid oxygen loss by tank valve
- build a hyperbaric setpoint linearity check device

I am undecided with respect of adding a mccr circuit. I could spoil solenoid awareness.
I'd very much like to have an independant passive sensor monitoring, or at least a possibility to view the sensors voltage output directly via the handsets.

Completing the class will not solve any of the above mentioned probs, but increase my confidence doing so.

ATB,
Matthias