Mark-15 4th cell

**Dave Sutton** · 6th March 2007, 01:27

OK, guys, popular demand dictates that I share my 4th cell installation for the Mark-15. We've debated the wisdom of a completely isolated PP02 system for rebreathers ad-nauseum, so let's not re-debate it. Bottom line is that I believe that every rig, no matter how sophisticated, ought to have a completely isolated way to measure PP02. In addition, on older rigs like my Mark-15 where integrated deco is not done, using a PP02 enabled computer for this tertiary PP02 system also gives deco calcs.

On the Mark-15, I have found that it's possible to place a 4th cell inside the counterlung area, right next to the inhale port, so that the loop gas can be measured right at the point where the gas passes into the breathing hose.

Essentially, I located a point on the center section that allows a cable to be passed into the interior of the rig from the center section, drilled a hole in the stainless steel center section, tapped the hole, added a gland, made a K1-D holder for the inside of the rig, and wired the whole thing up. The cell holder is machined Delrin and is held by one of the screws that holds the two pieces of the center section together (used a little longer screw).

The point where I exit the center section is right between the center section Bendix connection and the diluent face-seal for the ADV. This places the cable where it can be routed parallel to the Primary cable for exit from the case at the left shoulder.

Internally, the cable is secured inside the center section with cable ties, as depicted.

The sensor in use is actually rotated a few degrees counterclockwise as compred to the photos, I rotated it so the face of the sensor was able to be seen for the photos.

This is a clean and simple installation that has been well proven. I've just not had the rig apart for maintenance for a while so had not shot photos until tonight.

Photos ought to be self explainatory for any Mark-15 users. Mark-15.5 can be similarly modified, even easier actually since drilling the center section is easier with the plastic.

Questions gladly answered. Next Mark-15 projects I'll photograph are the external diluent and 02 blocks, offboard gas plumbing, and the internal weight system.

Just a note: The cable exit from the center secion looks long in the photos. It has the coil-spring strain relief installed, so the cable does not break at the exit. In the photos the spring is straight, making it look like a bulky fitting. It's not.

Enjoy,

Dave

SteveL · 6th March 2007, 12:13

Dave,

Nice - youve probably had that for years ...... I only looked at that idea a little while back and thought that while it is near perfect placement of the sensor I didnt do it for 3 main reasons.

1. for a completely independent o2 monitor (and I agree 100% that every rig should have one btw) I think it is good to be easily be able to calibrate in pure 02 - beling located inside make it harder to do this

2. a pain in the a#se to pull out if the molex connectors corrode or for some reason the cell popped out or crapped out.

3. Also wanted to use the same sensor as the main rig as I think its
a. a better sensor
b. nice to have output in air close to 21mV for cal /reality checks
c. spare if one of the main ones goes tits up on a trip away

While I havent done it yet I was thinking of tapping a hole just on the lower side of the inhale port and placing / epoxying a cell holder there (so similar placement) - need to cut a a hole in the case as well. This way it can be easily removed to check / varify calibration etc.

Haven't actually commited because

1. its a bigger hole - slightly bigger than a R10DS and those centre sections are like rocking horse sh*t with a price tag to match and im sure Im dumb enough to try it with a and drill and not in a jig - remind me I said that when i make mince meat of it.........

2. Concerned about a "glued" connection into an otherwise high integrity system.

3. bigger hole and a screw in connector are another failure point. Although there are plenty of inspos/ megs kisses etc that have a screw in 4th cell and we dont seem to hear of too many probs.

I have though about tapping right through the centre section and either threading / tapping the socket somehow and / or epoxying both sides.

Thinking this through do you think an 'obstruction' through the dual wall might negativly impact on the gas flow - cant see that it would as gas moving in this are is predominantly going down into the CL not blocking some little section of the scrubber.

Any thoughts

On the internal weight point I actually took my weight out so more convienient for travelling - get a tad more CL volume as well

This is just a piece of aluminium plate about 4mm thick.

Bolted through to the back plate -

I now put a couple of bullet weights in the carry handle and the trim seems OK -

Regards,

Steve

**Dave Sutton** · 6th March 2007, 12:58

Hi Steve, I actually stuck this up for you as we had discussed by PM previously...

In respect to most of the above:

(1): Pod calibration is done with the sensors in the rig, so doing the same thing for the 4th cell is just dandy.... (the error is essentially meaningless). Calibrate with the loop pressurized to the point of exhaust-valve opening, so its slightly above ambient and you'll always get a good cal.

(2): The system has been bulletproof reliable, no loose connectors, etc. Just as reliable as a hammer. All connections are soldered, shrink-wrapped, etc. Actually, the only connections are at the Molex. And you could, as I do on my other displays, simply solder the leads to the cell. You only do it annually anyhow. But it's not been an issue.

(3): If you look at the way I built it, you wil see that when the cell-holder is rotated counterclockwise into it's normal position, the cell-face is held by the air-duct for the inhale hose. The cell loads into the front of the holder and cannot slip out of the back (there is a machined setep internally in the holder), and cannot move forward, so it's entirely trapped.

(4): While I agree about carrying spare cells, I prefer to carry mine in sealed envelopes and not clanging around inside my rig...

(5): I would never use epoxy or bonding to try to make anything stick to a 15.5 center section. Anything added needs to be mechanically connected.

And..... is is better to dream about a perfect system or to have one that just works?....

Let's take the internal weight issue to another thread, as there are some things to consider (like making a plate so that the exhaust valve is triggered to open reliably....)

Dave

SteveL · 7th March 2007, 01:47

Quote: (Originally Posted by Dave Sutton)

Hi Steve, I actually stuck this up for you as we had discussed by PM previously...

thanks for that -

In respect to most of the above:

(1): Pod calibration is done with the sensors in the rig, so doing the same thing for the 4th cell is just dandy.... (the error is essentially meaningless). Calibrate with the loop pressurized to the point of exhaust-valve opening, so its slightly above ambient and you'll always get a good cal.

so you are calibrating the vr3 at 100% or telling the vr3 95% ?? or s=using the same gas as the main rig but at pressure and splitting the difference in the vr3 say 97.5%

(2): The system has been bulletproof reliable, no loose connectors, etc. Just as reliable as a hammer. All connections are soldered, shrink-wrapped, etc. Actually, the only connections are at the Molex. And you could, as I do on my other displays, simply solder the leads to the cell. You only do it annually anyhow. But it's not been an issue.

OK accept soldered connections - and annually OK as it should all come apart at lest that often anyway

(3): If you look at the way I built it, you wil see that when the cell-holder is rotated counterclockwise into it's normal position, the cell-face is held by the air-duct for the inhale hose. The cell loads into the front of the holder and cannot slip out of the back (there is a machined setep internally in the holder), and cannot move forward, so it's entirely trapped.

(4): While I agree about carrying spare cells, I prefer to carry mine in sealed envelopes and not clanging around inside my rig...

Me too for long trips the 4th cell spare is just a nice to have

(5): I would never use epoxy or bonding to try to make anything stick to a 15.5 center section. Anything added needs to be mechanically connected.

Thats why I havent done it yet - too chicken with the glue - do you think you can tap a thread on the center section OK or better to use an Oring seal on the outside and a retaining nut on the inside - aka bulkhead fisher connector did you machine a 'flat' on the outside so the o ring was not trying to seal on a curved surface?

And..... is is better to dream about a perfect system or to have one that just works?....

now as they say down here in Aus. - dont get all cocky just because Im still talking and you delivered

Let's take the internal weight issue to another thread, as there are some things to consider (like making a plate so that the exhaust valve is triggered to open reliably....)

Dave

Steve

**Dave Sutton** · 7th March 2007, 04:15

Hi Steve,

I'll just say from experience that the Molex has been just fine in the center section. The only moisture there is 100% distilled water... and the connection has been perfectly reliable. If you wanted to solder, you could, but I don't see the value.

I drilled the hole, threaded it, and then installed the gland and then *also* put the nut on the back. No need to machine a flat, it pulled down and sealed just fine. A 15.5 center section would be just the same, it's a hole drilled into plastic that's all.

The gland I use is a chrome plated brass one, accepting a 1.4 inch diameter cord. It has external male threads of 1/4 NPT and a backing nut as well., The face of the gland has a rubber seal to crush against the center section. I guess you could spot the plastic center section with an end mill to make a flat for mating, but I don't think it is required. On the metal center section the threads have enough mechanical advantage to actually flatten out the sheet metal so the seal is made.

VR-3 is calibrated at 100% 02, just like the pod (and as often...). Calibrate it when you do your pod and secondary calibrations and then forget about it until you do your next calibration routine. I do mine every month.

Going to go play with the new Oceanic digital HUD mask tomorrow night and to talk to the tech reps about soem software changes in gauge mode. I'll report tomorrow night.

Dave

6th March 2007, 12:58	#3 (permalink)
Dave Sutton Diveshop of Horrors Current Rebreather/s: Sport Kiss MK 15.X rEvo Other CCR Azimuth Home Build Other Rebreather/s: Classic Kiss rEvo Other CCR Azimuth Home Build Join Date: Jun 2006 Location: Narragansett, Rhode Island and Hackettstown, New Jersey Posts: 2,672	Re: Mark-15 4th cell Hi Steve, I actually stuck this up for you as we had discussed by PM previously... In respect to most of the above: (1): Pod calibration is done with the sensors in the rig, so doing the same thing for the 4th cell is just dandy.... (the error is essentially meaningless). Calibrate with the loop pressurized to the point of exhaust-valve opening, so its slightly above ambient and you'll always get a good cal. (2): The system has been bulletproof reliable, no loose connectors, etc. Just as reliable as a hammer. All connections are soldered, shrink-wrapped, etc. Actually, the only connections are at the Molex. And you could, as I do on my other displays, simply solder the leads to the cell. You only do it annually anyhow. But it's not been an issue. (3): If you look at the way I built it, you wil see that when the cell-holder is rotated counterclockwise into it's normal position, the cell-face is held by the air-duct for the inhale hose. The cell loads into the front of the holder and cannot slip out of the back (there is a machined setep internally in the holder), and cannot move forward, so it's entirely trapped. (4): While I agree about carrying spare cells, I prefer to carry mine in sealed envelopes and not clanging around inside my rig... (5): I would never use epoxy or bonding to try to make anything stick to a 15.5 center section. Anything added needs to be mechanically connected. And..... is is better to dream about a perfect system or to have one that just works?.... Let's take the internal weight issue to another thread, as there are some things to consider (like making a plate so that the exhaust valve is triggered to open reliably....) Dave __________________ "Changes in Lattitudes, Changes in Attitudes, Nothing remains quite the same".... www.nobubblediving.com
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7th March 2007, 01:47	#4 (permalink)
SteveL Custom Title Allowed! Current Rebreather/s: MK 15.X Other Rebreather/s: Inspiration Classic Join Date: Nov 2005 Location: Sydney Australia Posts: 222	Re: Mark-15 4th cell Quote: (Originally Posted by Dave Sutton) Hi Steve, I actually stuck this up for you as we had discussed by PM previously... thanks for that - In respect to most of the above: (1): Pod calibration is done with the sensors in the rig, so doing the same thing for the 4th cell is just dandy.... (the error is essentially meaningless). Calibrate with the loop pressurized to the point of exhaust-valve opening, so its slightly above ambient and you'll always get a good cal. so you are calibrating the vr3 at 100% or telling the vr3 95% ?? or s=using the same gas as the main rig but at pressure and splitting the difference in the vr3 say 97.5% (2): The system has been bulletproof reliable, no loose connectors, etc. Just as reliable as a hammer. All connections are soldered, shrink-wrapped, etc. Actually, the only connections are at the Molex. And you could, as I do on my other displays, simply solder the leads to the cell. You only do it annually anyhow. But it's not been an issue. OK accept soldered connections - and annually OK as it should all come apart at lest that often anyway (3): If you look at the way I built it, you wil see that when the cell-holder is rotated counterclockwise into it's normal position, the cell-face is held by the air-duct for the inhale hose. The cell loads into the front of the holder and cannot slip out of the back (there is a machined setep internally in the holder), and cannot move forward, so it's entirely trapped. (4): While I agree about carrying spare cells, I prefer to carry mine in sealed envelopes and not clanging around inside my rig... Me too for long trips the 4th cell spare is just a nice to have (5): I would never use epoxy or bonding to try to make anything stick to a 15.5 center section. Anything added needs to be mechanically connected. Thats why I havent done it yet - too chicken with the glue - do you think you can tap a thread on the center section OK or better to use an Oring seal on the outside and a retaining nut on the inside - aka bulkhead fisher connector did you machine a 'flat' on the outside so the o ring was not trying to seal on a curved surface? And..... is is better to dream about a perfect system or to have one that just works?.... now as they say down here in Aus. - dont get all cocky just because Im still talking and you delivered Let's take the internal weight issue to another thread, as there are some things to consider (like making a plate so that the exhaust valve is triggered to open reliably....) Dave Steve
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7th March 2007, 04:15	#5 (permalink)
Dave Sutton Diveshop of Horrors Current Rebreather/s: Sport Kiss MK 15.X rEvo Other CCR Azimuth Home Build Other Rebreather/s: Classic Kiss rEvo Other CCR Azimuth Home Build Join Date: Jun 2006 Location: Narragansett, Rhode Island and Hackettstown, New Jersey Posts: 2,672	Re: Mark-15 4th cell Hi Steve, I'll just say from experience that the Molex has been just fine in the center section. The only moisture there is 100% distilled water... and the connection has been perfectly reliable. If you wanted to solder, you could, but I don't see the value. I drilled the hole, threaded it, and then installed the gland and then also put the nut on the back. No need to machine a flat, it pulled down and sealed just fine. A 15.5 center section would be just the same, it's a hole drilled into plastic that's all. The gland I use is a chrome plated brass one, accepting a 1.4 inch diameter cord. It has external male threads of 1/4 NPT and a backing nut as well., The face of the gland has a rubber seal to crush against the center section. I guess you could spot the plastic center section with an end mill to make a flat for mating, but I don't think it is required. On the metal center section the threads have enough mechanical advantage to actually flatten out the sheet metal so the seal is made. VR-3 is calibrated at 100% 02, just like the pod (and as often...). Calibrate it when you do your pod and secondary calibrations and then forget about it until you do your next calibration routine. I do mine every month. Going to go play with the new Oceanic digital HUD mask tomorrow night and to talk to the tech reps about soem software changes in gauge mode. I'll report tomorrow night. Dave __________________ "Changes in Lattitudes, Changes in Attitudes, Nothing remains quite the same".... www.nobubblediving.com Last edited by Dave Sutton : 7th March 2007 at 04:24.
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