Mk5/109 Cleaned, Refreshed, and Upgraded

[agilis]

I have a 109 that is original unimproved just as I bought it 50 years ago but never used it. Basically new, shiny and lovely, a time capsule. I actually have a couple of 109s that have never been wet, along with the 109/MkV combo that I used a great deal for years and years. This combo has been upgraded, including the correct DIN kit on the Mk5. These days I mostly use a Mk19/D350 combo. At my age I like state of the art on my unfortunately infrequent dives.

 

[boat sju]

Yeah. Go Blue. You really?

Good point. But it is a different blue.

What you linked to is the diaphragm cover... It's the actual diaphragm in his that is blue.

oops, I wasn't thinking there.

 

[Ghost95]

Hi all, I have a question for you.

I'm working on the final tuning of the 109/256 I rebuilt and I'm noticing it doesn't breathe as easy as I'd like. What I mean it's that the cracking pressure seems a little high.

What I've found is that with the adjustment valve backed all the way out to the stop, and the office set just under free flow, it takes a little more effort to start the flow of air than I think it should.

I removed the stop and was able to back the adjustment knob out another turn or so so there was just a small leak and then I screwed the knob back in just until the leak stopped. The reg breath noticably easier with it set like that. It seems like spring pressure is causing the extra effort to start the flow of air.

Question is, do the springs in the 109 take a set or is there a way reduce the spring pressure so that I can screw the adjustment knob in enough to put the stop back in and keep the easy cracking pressure? Can I trim a coil if the spring to do this? Compress the spring and heat it?

The parts in this 109 conversion are a new S-Wing poppet, new curly foot lever, new spring, and old style balance chamber (the short one). The office is metal with a sharp knife edge and the LP seat is new with the poppet.

Thanks for any ideas. I'm not using a gauge to measure cracking pressure, just feel.

Have a good day.

 

[halocline]

Hi all, I have a question for you.

I'm working on the final tuning of the 109/256 I rebuilt and I'm noticing it doesn't breathe as easy as I'd like. What I mean it's that the cracking pressure seems a little high.

What I've found is that with the adjustment valve backed all the way out to the stop, and the office set just under free flow, it takes a little more effort to start the flow of air than I think it should.

I removed the stop and was able to back the adjustment knob out another turn or so so there was just a small leak and then I screwed the knob back in just until the leak stopped. The reg breath noticably easier with it set like that. It seems like spring pressure is causing the extra effort to start the flow of air.

Question is, do the springs in the 109 take a set or is there a way reduce the spring pressure so that I can screw the adjustment knob in enough to put the stop back in and keep the easy cracking pressure? Can I trim a coil if the spring to do this? Compress the spring and heat it?

The parts in this 109 conversion are a new S-Wing poppet, new curly foot lever, new spring, and old style balance chamber (the short one). The office is metal with a sharp knife edge and the LP seat is new with the poppet.

Thanks for any ideas. I'm not using a gauge to measure cracking pressure, just feel.

Have a good day.

The reason your 109 doesn't breathe as well has to do with either the lever or the spring. Unfortunately, the best you can do is experiment. You've replaced all the right parts. (although the longer balance chamber that fully captures both o-rings on the S wing poppet would be a good thing to get)

Here's how I approach these regs, and I've worked on dozens of them. One thing you should understand is that there is some variance in their performance no matter what I've tried. It's hard to know what you consider 'too high' for cracking pressure. With mine, once I've tried several lever/poppet/spring combinations I can usually get them to what I consider very comfortable. Not like the best D series regs, those can be stable under 1" of cracking pressure, but something most divers would consider very easy to breathe. (I don't have a magnehelic to measure with)

Start by adjusting the orifice so that it eliminates any leak without the diaphragm on. (An inline tool is nice for this but not necessary) Once that's done, leave it pressurized and lay the diaphragm in place, put the rubber cover over it and then press the chrome cover in place. See if it starts leaking, it probably will. Then you have to adjust out that leak; you're actually lowering the lever height. If you have to adjust it substantially, that means that the lever is just too high. What I do at this point is open my stash of levers and start trying to find one that sits a little lower. We're talking about pretty small differences. As an alternative, you could try adjusting the lever. There is an old tool for that; pretty sure Couv had one. Doing it freehand is tough, I wouldn't try it. Basically what the tool does is clamp the feet tightly and allow you to increase the angle between the feet and the arms of the lever.

On to the spring discussion....there are definitely differences in the tension of those SP springs. A story I once heard was that SP used higher consistency springs for the G250, while the less 'in spec' ones were used in the downstream 2nds like R190. The part numbers are the same, you can look that up. The SP techs assembling these regs and choosing the springs might have had some sort of fancy tool to actually measure the spring tension; I have no idea. What I did is buy several of them and I just do trial and error until I find one that works well. If you get the lever height correct then the spring doesn't matter as much.

There's another possibility; there could be slight variances in the diaphragms, which means that maybe you have one that's a little 'short' and presses more against the lever. I've tried swapping diaphragms, but I don't have a stash of those, usually I'll take one out of a reg that's working great just to try it. Sometimes it makes a small difference.

Then there is the side issue of the square holes in the air barrel. If you can reach there with a tiny file, you can clean those up, make sure there's no burr and everything is nice and square. I've had some occasional success with that in that it makes the action smoother.

For me, 90% of the time a new curly-foot lever and spring does the job, but there are some, usually the older 109s, that are just more finicky. I put up with it because I love using these old metal 2nds in cave diving. They help with drymouth on 2-3 hr dives (which I do frequently) and I don't worry about them getting cracked when I have to drag tanks in and out of the water in rocky, slippery entrances. (Sidemount, so you enter the water without tanks on then pull them off the rocks) I also don't worry about them on stages that get left in the cave and might get bumped around by mistake.

Good luck, at least I've provided you with some reading material!

 

[Ghost95]

The reason your 109 doesn't breathe as well has to do with either the lever or the spring. Unfortunately, the best you can do is experiment. You've replaced all the right parts. (although the longer balance chamber that fully captures both o-rings on the S wing poppet would be a good thing to get)

Here's how I approach these regs, and I've worked on dozens of them. One thing you should understand is that there is some variance in their performance no matter what I've tried. It's hard to know what you consider 'too high' for cracking pressure. With mine, once I've tried several lever/poppet/spring combinations I can usually get them to what I consider very comfortable. Not like the best D series regs, those can be stable under 1" of cracking pressure, but something most divers would consider very easy to breathe. (I don't have a magnehelic to measure with)

Start by adjusting the orifice so that it eliminates any leak without the diaphragm on. (An inline tool is nice for this but not necessary) Once that's done, leave it pressurized and lay the diaphragm in place, put the rubber cover over it and then press the chrome cover in place. See if it starts leaking, it probably will. Then you have to adjust out that leak; you're actually lowering the lever height. If you have to adjust it substantially, that means that the lever is just too high. What I do at this point is open my stash of levers and start trying to find one that sits a little lower. We're talking about pretty small differences. As an alternative, you could try adjusting the lever. There is an old tool for that; pretty sure Couv had one. Doing it freehand is tough, I wouldn't try it. Basically what the tool does is clamp the feet tightly and allow you to increase the angle between the feet and the arms of the lever.

On to the spring discussion....there are definitely differences in the tension of those SP springs. A story I once heard was that SP used higher consistency springs for the G250, while the less 'in spec' ones were used in the downstream 2nds like R190. The part numbers are the same, you can look that up. The SP techs assembling these regs and choosing the springs might have had some sort of fancy tool to actually measure the spring tension; I have no idea. What I did is buy several of them and I just do trial and error until I find one that works well. If you get the lever height correct then the spring doesn't matter as much.

There's another possibility; there could be slight variances in the diaphragms, which means that maybe you have one that's a little 'short' and presses more against the lever. I've tried swapping diaphragms, but I don't have a stash of those, usually I'll take one out of a reg that's working great just to try it. Sometimes it makes a small difference.

Then there is the side issue of the square holes in the air barrel. If you can reach there with a tiny file, you can clean those up, make sure there's no burr and everything is nice and square. I've had some occasional success with that in that it makes the action smoother.

For me, 90% of the time a new curly-foot lever and spring does the job, but there are some, usually the older 109s, that are just more finicky. I put up with it because I love using these old metal 2nds in cave diving. They help with drymouth on 2-3 hr dives (which I do frequently) and I don't worry about them getting cracked when I have to drag tanks in and out of the water in rocky, slippery entrances. (Sidemount, so you enter the water without tanks on then pull them off the rocks) I also don't worry about them on stages that get left in the cave and might get bumped around by mistake.

Good luck, at least I've provided you with some reading material!

Thanks for the info. The long read wasn't an issue and the detail was good because the method you described is almost exactly the way I did things.

I don't have a supply of new style levers, springs, or diagrams so I'm looking at modifying what I do have. I really feel it's the spring tension that's causing the issue though.

There is very little movement of the diaphragm before I get a purge and like I said, removing the adjustment stop and backing the knob out an extra turn the breathing gets noticably easier. That's why I think it's the spring. I'll see if i can find some springs with less tension or risk it and modify one.

Thanks again for the info.

 

[halocline]

There is very little movement of the diaphragm before I get a purge and like I said, removing the adjustment stop and backing the knob out an extra turn the breathing gets noticably easier. That's why I think it's the spring. I'll see if i can find some springs with less tension or risk it and modify one.

Thanks again for the info.

The way to evaluate the lever is to see how much you need to drop it to stop the leak once the diaphragm is installed. I don't think the 'tight' purge is an issue, because having to press the purge button any sort of distance before hearing air flow is an indication that the lever is too low. That almost never happens with these regs, the issue is usually that the lever is too high. This is why it's good to adjust the reg to just stopping air leaking without the diaphragm in place, then seeing how much you need to tighten the orifice (dropping the lever) to stop it again once the diaphragm is in place. If it's more than, say, 1/4 turn, then that's an issue that will affect the performance. You may have already done that and determined that the lever height is good. I'm only mentioning it again because it is the usual culprit.

You certainly could be right about it being the spring, but IME the variance in the springs is not as crucial as the lever height. Those springs (last time I bought some) were not that expensive, so you could buy 3 or 4 of them and try. If you have any other 109s or G250s that are working well you can swap out the spring just to see if it makes any difference.

You could try a new balance chamber too. That's just a guess, but maybe there is something with the fit between the chamber and the spring. It's a long shot.

 

[Ghost95]

I think the lever is good. Very little if any play when purge is pressed to air flow. Maybe the balance chamber and I'll look at that issue but I'm still leaning to spring tension. I'll try a spring from a good G250 and see what that feels when I get home.

Thanks for the discussion.

 

[halocline]

I think the lever is good. Very little if any play when purge is pressed to air flow. Maybe the balance chamber and I'll look at that issue but I'm still leaning to spring tension. I'll try a spring from a good G250 and see what that feels when I get home.

Thanks for the discussion.

Sorry to be persistent, but 'little to no play when the purge is pressed' is not how you evaluate lever height for this situation. You need to go through that process of adjusting without the diaphragm in place, backing out the orifice (counter clockwise) until a leak starts, then clockwise just until the leak stops. Then install the diaphragm and if it still doesn't leak, count yourself very lucky. But it probably will, so adjust the leak out (clockwise). If it takes a lot, your lever height is off, and you are compensating for that by tightening the orifice more to drop the height.

If you are doing this already, I apologize, but your reply didn't indicate that you understand specifically what I've been describing. Adjusting lever height independently of orifice pressure is something you can do on some 2nd stages, but not this one. Taking the 'play' out of the lever does not apply to this 2nd stage design.

 

[Ghost95]

Thanks. I did install and adjust the orfice without the diaphragm installed first. It did not leak when I put the diaphragm on with the other parts.

I'll try it again just for grins incase I missed something but I think it was as you described.

Sorry for the confusion in my exploration.

 

[Angelo Farina]

Adjusting lever height independently of orifice pressure is something you can do on some 2nd stages, but not this one. Taking the 'play' out of the lever does not apply to this 2nd stage design.

Actually you can, but it requires to distort the lever over a calibrated height reference. Most people prefer to switch to another lever instead of distorting your one.
Same with the spring: they are not all exactly the same length/stiffness. In principle it is possible to adjust their length by distorting the coil, but most people prefer simply to swap the spring with another slightly longer or shorter, as required.
more info here: Scubapro Second Stage Lever Height