OP
Ojai Diver
Contributor
Agreed, it may not be worth adjusting, but I am interested in everybody's thoughts on this.
Tuning Scubapro A 700 reg
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Everything you've read above is correct. Each of the posters has a point. Nonetheless, I understand your desire to eke just "a little more performance" out of your expensive toy. Search SB for threads on "Case Geometry Fault" and you'll learn why folks are advising you against what you are trying to do. Nonetheless, you can indeed tune the A700 down as low as 0.7" or even a bit lower, with a new seat. What that means in practice, however, is that it will perform that nicely (and easy breathers are indeed a pleasure to dive) in only ONE position: standard 45 degree face down diving position. If you look straight down, the exhalation valve will be higher than 0.7" above the middle of the diaphragm, and the reg will begin to gently freeflow. As another poster mentioned, this is a cold water hazard. But try it out, if you're a warm water diver! It'll be fun. And you can always tune it back. The case geometry fault is smaller with the A700 than with the G250/260 series, because the case is smaller. But with this shape reg (as opposed to regs like Poseidons and Hollis 500e's with coaxial diaphragm and exhaust valve), there's a physical limit to how lightly you can have the seat rest on the orifice, before differential water pressure between the diaphragm and the exhaust valve takes over and causes the valve to open (freeflow). Oh! Did I forget to say SCUBAPRO D-400??!! 
Tuning is indeed sort of done from both ends of the barrel (see pic):
The lever height and general pressure on the seat is governed by how far in you screw the orifice (on the right side of this pic). That would NOT be where I'd start this adventure. ASSUMING your shop has correctly tuned the reg in the first place, sealing pressure on the seat and lever height have already been set correctly. Therefore, as you were told by your tech, lowering your cracking effort alone, will be accomplished by counterclockwise screwing of the microadjust screw inside the knob.
Pry the little label off the knob, and unscrew the set screw inside the knob so you can pull it off. PAY ATTENTION to how gently that screw was set. When you replace your knob, you do not want to overtorque that screw. It's ONLY to hold the knob on. PM me if you want me to send you a replacement decal after you're done.
Once the knob is off, using a small flat-bladed screwdriver (3-4mm), start to unscrew the micro adjust while your reg is in the sink and pressurized. Lower the reg with the diaphragm parallel to the water and with the mouthpiece straight up. Then find and mark with a piece of tape the point at which the water level in the sink causes the second stage to JUST BEGIN to hiss. Then (assuming that's 1.1" of cracking effort) hold the reg with your tape mark 0.2" higher. Unscrew the microadjust until the reg JUST BEGINS to hiss. Bingo, you're done. Now tuned to 0.9" of water. Replace the knob, dry everything off perfectly and stick a new decal back on.
A700 Service Technician
Tuning is indeed sort of done from both ends of the barrel (see pic):
The lever height and general pressure on the seat is governed by how far in you screw the orifice (on the right side of this pic). That would NOT be where I'd start this adventure. ASSUMING your shop has correctly tuned the reg in the first place, sealing pressure on the seat and lever height have already been set correctly. Therefore, as you were told by your tech, lowering your cracking effort alone, will be accomplished by counterclockwise screwing of the microadjust screw inside the knob.
Pry the little label off the knob, and unscrew the set screw inside the knob so you can pull it off. PAY ATTENTION to how gently that screw was set. When you replace your knob, you do not want to overtorque that screw. It's ONLY to hold the knob on. PM me if you want me to send you a replacement decal after you're done.
Once the knob is off, using a small flat-bladed screwdriver (3-4mm), start to unscrew the micro adjust while your reg is in the sink and pressurized. Lower the reg with the diaphragm parallel to the water and with the mouthpiece straight up. Then find and mark with a piece of tape the point at which the water level in the sink causes the second stage to JUST BEGIN to hiss. Then (assuming that's 1.1" of cracking effort) hold the reg with your tape mark 0.2" higher. Unscrew the microadjust until the reg JUST BEGINS to hiss. Bingo, you're done. Now tuned to 0.9" of water. Replace the knob, dry everything off perfectly and stick a new decal back on.
A700 Service Technician
Last edited:
OP
Ojai Diver
Contributor
Everything you've read above is correct. Each of the posters has a point. Nonetheless, I understand your desire to eke just "a little more performance" out of your expensive toy. Search SB for threads on "Case Geometry Fault" and you'll learn why folks are advising you against what you are trying to do. Nonetheless, you can indeed tune the A700 down as low as 0.7" or even a bit lower, with a new seat. What that means in practice, however, is that it will perform that nicely (and easy breathers are indeed a pleasure to dive) in only ONE position: standard 45 degree face down diving position. If you look straight down, the exhalation valve will be higher than 0.7" above the middle of the diaphragm, and the reg will begin to gently freeflow. As another poster mentioned, this is a cold water hazard. But try it out, if you're a warm water diver! It'll be fun. And you can always tune it back. The case geometry fault is smaller with the A700 than with the G250/260 series, because the case is smaller. But with this shape reg (as opposed to regs like Poseidons and Hollis 500e's with coaxial diaphragm and exhaust valve), there's a physical limit to how lightly you can have the seat rest on the orifice, before differential water pressure between the diaphragm and the exhaust valve takes over and causes the valve to open (freeflow). Oh! Did I forget to say SCUBAPRO D-400??!!
Tuning is indeed sort of done from both ends of the barrel (see pic):
View attachment 460204
The lever height and general pressure on the seat is governed by how far in you screw the orifice (on the right side of this pic). That would NOT be where I'd start this adventure. ASSUMING your shop has correctly tuned the reg in the first place, sealing pressure on the seat and lever height have already been set correctly. Therefore, as you were told by your tech, adjusting your cracking effort alone, will be accomplished by counterclockwise screwing of the microadjust screw inside the knob.
Pry the little label off the knob, and unscrew the set screw inside the knob so you can pull it off. PAY ATTENTION to how gently that screw was set. When you replace your knob, you do not want to overtorque that screw. It's ONLY to hold the knob on. PM me if you want me to send you a replacement decal after you're done.
Once the knob is off, using a small flat-bladed screwdriver (3-4mm), start to unscrew the micro adjust while your reg is in the sink and pressurized. Hold the reg with the diaphragm parallel to the water and with the mouthpiece straight up. Then find and mark with a piece of tape the point at which the water level in the sink causes the second stage to JUST BEGIN to hiss. Then (assuming that's 1.1" of cracking effort) hold the reg with your tape mark 0.2" higher. Unscrew the microadjust until the reg JUST BEGINS to hiss. Bingo, you're done. Now tuned to 0.9" of water. Replace the knob, dry everything off perfectly and stick a new decal back on.
A700 Service Technician
RSingler,
This is an excellent response, and I am grateful. And intrigued.
Questions:
I dive in 50-65 F. Pacific water. I understand the instability you mention at .7 If set to .9, would this be stable in all positions? Or would I have to experiment to know?
Could leaks/free flows be corrected while diving using the adjustment knob?
Should this adjustment be done at low tank pressure?
As the seat wears, will I have to tighten the micro adjust?
Thanks!
At 0.9" you just might get away with it except vertical head down in the water.
Yes, just screw in the adjustment knob. That's all the micro adjust is doing - limiting how far OUT you can unscrew things. Easy fix.
1/4 to half a turn in should do it.
Don't sweat the tank pressure. The Mk11 is just a non-environmentally sealed Mk17. Great reg! Should shift IP upwards around 8psi max, from full tank to empty. But it doesn't matter. Your balanced second stage doesn't care about +/- 8 psi. Heck, it doesn't care much about -50 psi! You can breath that reg on an empty tank and won't see it pull hard until tank is around 200 psi, depending upon depth. At that point, you're OOA, and without warning, if you haven't watched your gauges. Completely different from the old days of unbalanced firsts AND seconds, which (with pistons at least) would give progressively greater breathing effort as the tank emptied.
As the seat takes a set (groove) there is progressively less and less pressure placed by the orifice on the seat (as the groove retracts away from the orifice' knife edge). Add'l pressure on the micro adjust MIGHT help, up until the seat breaks seal from the orifice at a given IP. No, that fix is done by adding pressure from the orifice side. But this is why service techs can sort-of make a living - that's a very precise adjustment which I wouldn't recommend attempting from a book or explanation. Seat pressure also governs lever height, which governs how far open you can suck your valve. That begins to become a safety factor, as the difference between proper adjustment and dangerous lever rattle is often less than half a turn. You need some hands-on guidance with that one, I'd say. It CAN be done safely without a shop full of tools. Heck, Scubaboard is filled with DIY'ers that do just fine. We love to criticize shop service quality, and with good cause. That said, it's pretty easy to get dangerous if you play with the balance between seat pressure and poppet spring pressure.
My 2 cents.
Yes, just screw in the adjustment knob. That's all the micro adjust is doing - limiting how far OUT you can unscrew things. Easy fix.
1/4 to half a turn in should do it.
Don't sweat the tank pressure. The Mk11 is just a non-environmentally sealed Mk17. Great reg! Should shift IP upwards around 8psi max, from full tank to empty. But it doesn't matter. Your balanced second stage doesn't care about +/- 8 psi. Heck, it doesn't care much about -50 psi! You can breath that reg on an empty tank and won't see it pull hard until tank is around 200 psi, depending upon depth. At that point, you're OOA, and without warning, if you haven't watched your gauges. Completely different from the old days of unbalanced firsts AND seconds, which (with pistons at least) would give progressively greater breathing effort as the tank emptied.
As the seat takes a set (groove) there is progressively less and less pressure placed by the orifice on the seat (as the groove retracts away from the orifice' knife edge). Add'l pressure on the micro adjust MIGHT help, up until the seat breaks seal from the orifice at a given IP. No, that fix is done by adding pressure from the orifice side. But this is why service techs can sort-of make a living - that's a very precise adjustment which I wouldn't recommend attempting from a book or explanation. Seat pressure also governs lever height, which governs how far open you can suck your valve. That begins to become a safety factor, as the difference between proper adjustment and dangerous lever rattle is often less than half a turn. You need some hands-on guidance with that one, I'd say. It CAN be done safely without a shop full of tools. Heck, Scubaboard is filled with DIY'ers that do just fine. We love to criticize shop service quality, and with good cause. That said, it's pretty easy to get dangerous if you play with the balance between seat pressure and poppet spring pressure.
My 2 cents.
OP
Ojai Diver
Contributor
It's not a concern in making this adjustment, no. Your A700 will tolerate a WIDE variety of IP's, and in any case, he tuned your second stage to your first, presumably.
But buy an IP gauge, or make one. Definitely! How to make an IP gauge?
If you are using the term "IP creep", then that is something you should be checking before every dive trip. Indeed, I check IP every day of diving. It's just an early step when I put my gear together (though if I know my regs, I don't then bother to wait around 5 min to watch for creep). Takes 20 sec, and then I attach my hose to my LPI and continue setting up. If I get my expected IP and it locks right up, and it doesn't drop more than 15-20 psi on a quick purge and then locks up again, I know I've got a good first stage for that dive. When it isn't like that EVERY TIME, you know you've waited too long between services.
But buy an IP gauge, or make one. Definitely! How to make an IP gauge?
If you are using the term "IP creep", then that is something you should be checking before every dive trip. Indeed, I check IP every day of diving. It's just an early step when I put my gear together (though if I know my regs, I don't then bother to wait around 5 min to watch for creep). Takes 20 sec, and then I attach my hose to my LPI and continue setting up. If I get my expected IP and it locks right up, and it doesn't drop more than 15-20 psi on a quick purge and then locks up again, I know I've got a good first stage for that dive. When it isn't like that EVERY TIME, you know you've waited too long between services.
OP
Ojai Diver
Contributor
Okay. Thank you so much!
halocline
Contributor
I would definitely get an IP gauge and check your IP with a full tank and at about 500 PSI. You can do this with a full tank, just close the valve, and take a few small breaths until the SPG reads 500. If the tech set it "on the high side" with a full tank, it might be too high at 500.
If you tinker around with this reg and are still not happy, buy an old D series 2nd stage (D300-350-400) and that should take care of things. Be careful, once you start tinkering its a slippery slope to DIY service, buying old regs and adopting a somewhat dark attitude to the scuba gear sales industry.
OP
Ojai Diver
Contributor
Following up on this post:
I took Halocline's advice and bought an IP gauge. These are the numbers:
1600 psi: IP is 139
500 psi: IP is 148
The IP does not creep.
These numbers are somewhat approximate as this gauge is rather small to read with precision.
I have some newbie questions:
What are the specs? Are these numbers acceptable?
I note that the Mark 11 has on each side an Allen key fitting. Which side adjusts IP? I assume that clockwise decreases IP, yes?
I also note, out of water (not in the water) the A700 honks on exhalation. Is this a problem?
On the inches of water (.8, .9 etc.) I assume these are tenths of an inch. I don't have any such ruler, so I guess I have to convert?
Thanks!
I took Halocline's advice and bought an IP gauge. These are the numbers:
1600 psi: IP is 139
500 psi: IP is 148
The IP does not creep.
These numbers are somewhat approximate as this gauge is rather small to read with precision.
I have some newbie questions:
What are the specs? Are these numbers acceptable?
I note that the Mark 11 has on each side an Allen key fitting. Which side adjusts IP? I assume that clockwise decreases IP, yes?
I also note, out of water (not in the water) the A700 honks on exhalation. Is this a problem?
On the inches of water (.8, .9 etc.) I assume these are tenths of an inch. I don't have any such ruler, so I guess I have to convert?
Thanks!
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