Upgrading R109 to 156

[bbkid]

Hello all,

I found a complete SP MK7/109/109 combination with guages and hoses at a local pawnshop and couldn't leave it behind for $80.00. (They threw in a pink dive knife too.) I started with a MK7 and thought it might be a good starter for my daughter who will take lessons this summer.

At the time I bought this rig I didn't know that some of the MK7's were not rated for 3000 psi. I used mine on AL 80's all the time not knowing any better. The new reg has the small yolk as I am sure my old one did. Have there ever been failures reported?

Where can I get the parts to convert one of the two R109's to a 156? Is there a kit number?

Thanks,

bbkid

 

[halocline]

First thing is to stop saying "R". It's just the number. The parts you need are:
1 G250 poppet
1 G250 spring
1 G250 balance chamber

and a rebuild kit, or more accurately, a seat , 902 and 012 (I think) o-rings. The actual part numbers are on my other hard drive, but awap probably has them memorized. If you want to be totally safe and trouble free you could get the G250 lever; some older levers have a compatibility problem with the G250 poppet. It's hard to know until you put it together how the lever/poppet fit is, but the easiest (and most expensive, unfortunately) approach is to get the new lever.

The Mk7 lightest yoke is not something I'd use on a 3000 PSI tank. It won't break off and decapitate your daughter, but it will probably stretch a bit and leak. Just get her a nice 5 port Mk5. It'll cost you all of $40, and she'll have the coolest reg on the block. If she gripes about the heavy 2nd stage, just get her a seacure. The newer model without the rigid yellow collar fits very well on the 109.

 

[Couv]

Zung posted an annotated G250 diagram here: http://www.scubaboard.com/forums/5127724-post134.html it has all the parts and o-ring sizes listed....good man that Zung.

Here is a thread you may find helpful re the MK7. It has a diagram with the o-ring sizes etc too. http://www.scubaboard.com/forums/regulators/366221-light-yoke-vs-heavy-yoke.html#post5676128 I might even have a heavy yoke MK7 hiding in my closet somewhere if you really need one.....it'll be expensive though, not because I rebuilt it, but because I don't like going into my closet. ;-) if I can't find mine or you can't afford it, I think Awap probably has 30 or 40 that he uses for ballast. He's better than me and cheaper.

Edit: Just noticed you're new here. Welcome to Scuba Board!

 

[Zung]

Disclamer: I did NOT post that diagram out of my own free will. I was ORDERED to post it by... mon frère couv

If you have issues finding the parts in the US, think global. A good place to start is the 'Bay, just substitue .co.uk or .ie to .com. Same language (more or less), more options. The older service kits with the poppet come up fairly regularly, but the balance chamber, the spring, and the lever can be a problem.

 

[herman]

Welcome to the board.

On a slightly differnet note, why bother to convert them in the first place? The breathing difference from what I can gather based on some research and talking with some folks who's opinion I respect, is minimual at best and you add more components. I choose not to convert mine for that reason.

 

[redacted]

I tend to go with a balanced primary (156) and an unbalanced alternate (109) but the difference is little to unnoticeable. Have you opened them up yet to see if either has already been converted. In any case, they almost surely have the older style poppets so you will need to find the new style poppet assemblies. Older G250 kits included the poppet assembly and some included the balance chamber. Current G200 kits include the duro poppet you will probably need for the 109. The spring for the 156 is the same as the R-series spring so they should be readily available if you can find a parts source.

Captain has talked about using the lighter yokes on 3000 psi tanks with no problem. But a newer Mk5 makes good sense. That 2 lb block of a Mk7 could give a little lady some trim problems, where fat old men need the help.

 

[DA Aquamaster]

The orifice, the diaphragm and the lever are the same in both the 109 and 156 and if properly adjusted, the net forces acting on the seat will be the same. Consequently, if properly adjusted a 109 and a 156 will give identical performance when used on a balanced first stage.

To get picky on the issue, the Mk 1, Mk 5, Mk 6, Mk 7, Mk 8, Mk 9, Mk 10 and Mk 10+ are NOT perfectly balanced as they use a straight piston stem and unflared tip, so the area of the knife edge itself is not balanced. This results in a 4-6 psi change in IP (depending on piston head size) as tank pressure drops. But practically speaking you won't notice the difference in inhalation performance.

As noted above some levers are not compatible with the latest s-wing poppet or the latest duro poppet. But those levers were made in the late 1960's and can be identified by their slightly wider and non stepped tabs. If the levers are not compatible you will definitely feel it, so it is not something you can easily miss. The current G250V lever works fine.

Also as noted above you need:
1. An S-wing poppet (no longer included in annual service kits)
2. A G250/G250V Balance Chamber (they came in black, white and silver/grey colors, different lengths and in a couple different styles, but they all work fine)
3. A G250 spring
4. A rivet style seat (used in all of the SP balanced second stages as well as the new unbalanced C200 and C300)

I agree the Mk 7 is a boat anchor and a less than optimum choice. The air side of it is a Mk 5 and the other side contains the "honk" function. In most cases the honk function no longer works, parts are no longer to fix it and most techs can't work on it because they have never seen one. Yyou are far better off with a Mk 5 or a Mk 10 as both are still in common use and are superb first stages that are still "modern" in terms of layout and design.

Normally I'd offer one of each for the conversion, but my private stock has been pretty much depleted and I only have 1 spring left and I probably need to order more for the regs I stumble upon for my own use. (I keep my personal and/or vintage parts separate from the shop parts). I also don't compete directly with the shop but run the service work through them. If you want to have it converted send me a PM and I'll arrange to have it run through the shop and I'll have them order the parts needed for the conversion.

The other issue with 109s and 156s is that the rubber purge covers dry rot and the exhaust T's go bad and crack. The shop does have new rubber purge covers in stock and it also has used very good condition exhaust T's off some retired rental regs.

I also have some nice Mk 5's and a couple Mk 15's I'd sell if you want something different than the Mk 7.

 

[halocline]

You'd be smart to take DA up on his offer; you'll get everything done at once, expertly, and you'll get the right 1st stage. I was going to mention the rubber parts; unless those are in excellent condition, I'd go ahead and replace them. They are available, but you never know, they could become scarce.

One nit-pick, and I can't believe I'm nit-picking with the all-time scubaboard co-MVP of regulator knowledge, (the other being Luis) is that the forces on the unbalanced and balanced seat are not exactly identical. Because the force on the balanced seat is a combination of spring and air pressure from the balance chamber, when IP drops during inhalation, so does the pressure in the balance chamber, and consequently on the seat itself. This does not effect cracking effort, but does theoretically mean that once inhalation is initiated, effort to keep the seat open is lower. In my meager experience, I do seem to generally notice a difference between my converted 109s and non-converted, but it's very slight and I probably wouldn't notice a difference on a blind test.

 

[Zung]

... The spring for the 156 is the same as the R-series spring so they should be readily available if you can find a parts source...

Thanks, that's a piece of valuable information: parts #01020216 for/from the R190/290/295/380/390/395 are common as dirt since every SP backed dive club use them.

Now that you got me curious, I checked and the G500, the S550/600 also use the same spring.

People have no imagination.

BTW, I keep one of my 109 unbalanced for an A/B test. I'll report back as soon as the waters hit 70°F. I have the feeling I'll come to the same conclusion as halocline. But then I'm the heretic who dared declare publicly that my G250 breathes better than my 109 BA.

 

[bbkid]

I think I'll chock this one up to experience and look for a newer lighter regulator combination. Daughter likes the pink knife at least.

Cheers.

bbkid