Regulator Resistance Adjustment on My ScubaPro MK25/600T

[rmarsh3309]

My fiancee and I have the same reg and have noticed no difference in breathing resistance no matter where we set the resistance adjustment.

It's not apparent the Dive/Pre-Dive knob has any effect on free-flow behavior either.

Am I missing something?

 

[lhpdiver]

I'm sure others here will give you better technical explanations, but my MK25/S600 has hundreds of dives on it and every one of them has been in PreDive exclusively.

 

[redacted]

I assume you are talking about the VIVA feature which is licated by the mouthpiece and has about 1/4 turn adjustment. Its effect is rather subtle. It simply impedes the air flow into the mouthpiece. It is effective at high flow rates thus preventing strong freeflows in the "predive" position. The adjustment knob is the inhalation resistance control. It makes 2 or 3 full turns. If you can't tell any difference with that adjustment, you might as well drink MD 20/20 with your ribeye steak! The effects of that adjustment should be very noticable, even if you are just sitting on the couch.

 

[rmarsh3309]

I assume you are talking about the VIVA feature which is licated by the mouthpiece and has about 1/4 turn adjustment. Its effect is rather subtle. It simply impedes the air flow into the mouthpiece. It is effective at high flow rates thus preventing strong freeflows in the "predive" position. The adjustment knob is the inhalation resistance control. It makes 2 or 3 full turns. If you can't tell any difference with that adjustment, you might as well drink MD 20/20 with your ribeye steak! The effects of that adjustment should be very noticable, even if you are just sitting on the couch.

Sheez, EVERYBODY knows Colt 45 malt liquor is the proper accompaniment for ribeye!

But anyways... back to the reg... I've turned the resistance from stop-to-stop and couldn't really notice a harder pull. But I've never tried it deeper than 15' or so. Maybe I just have a powerfull diaphragm. My fiancee has a heck of a set of lungs on her come to think of it... this thread is kinda getting off topic isn't it?

 

[redacted]

Sheez, EVERYBODY knows Colt 45 malt liquor is the proper accompaniment for ribeye!

But anyways... back to the reg... I've turned the resistance from stop-to-stop and couldn't really notice a harder pull. But I've never tried it deeper than 15' or so. Maybe I just have a powerfull diaphragm. My fiancee has a heck of a set of lungs on her come to think of it... this thread is kinda getting off topic isn't it?

Which adjustment are you turning? The large round knob on the end of the barrel opposite the hose of the small flat knob up behind the mouthpiece?

 

[rmarsh3309]

Which adjustment are you turning? The large round knob on the end of the barrel opposite the hose of the small flat knob up behind the mouthpiece?

Thanks for following up AWAP.

I'm certain I'm adjusting the right knob - and it's clearly marked with a + and -. I'm wondering if the LDS that did my initial setup and annuals has done something to limit the effect of this adjustment.

I take it you have a similar reg? And the resistance adjustment has a pronounced effect?

 

[redacted]

Thanks for following up AWAP.

I'm certain I'm adjusting the right knob - and it's clearly marked with a + and -. I'm wondering if the LDS that did my initial setup and annuals has done something to limit the effect of this adjustment.

I take it you have a similar reg? And the resistance adjustment has a pronounced effect?

The +/- is on a "decal" at the end of the adj knob. My wife & I both use one. The adjustment should have a very noticable effect. If you fill a sink with water you can check the cracking pressure which is effected by that knob. With the regulator pressurized, knob all the way out (top of knob turned forward with reg in mouth) and mouthpiece facing up, slowly lower the reg into the water. It should start flowing about as the mouthpiece hits the water +/- 1/4 inch. With the knob turned all the way in, you may get water flowing onto the reg before the gas flows. If not, have your LDS check it out. I can't imagine what would keep that feature from working.

 

[redacted]

It should start flowing about as the mouthpiece hits the water +/- 1/4 inch. With the knob turned all the way in, you may get water flowing onto the reg before the gas flows.

OK, I checked mine out. With the adj knob all the way out, the knob should have about 1/16 inch clearance with the body and gas should flow well before the water gets to the mouthpiece. Mine flows about 1/3 of the way up the VIVA decal or about 1/2 inch below the mouthpiece.

With it cranked all the way in, the knob contacts the body and flos starts just as water starts running into the comfobite mouthpiece. Std mouthpiece may be just a bit longer so gas flow may occur a little before the mouthpiece submerges.

The 1/16 of an inch difference is actually compressing the spring by that much. I still can't imagine how that could be disabled by mistake.

 

[lhpdiver]

OK, I checked mine out. With the adj knob all the way out, the knob should have about 1/16 inch clearance with the body and gas should flow well before the water gets to the mouthpiece. Mine flows about 1/3 of the way up the VIVA decal or about 1/2 inch below the mouthpiece.

With it cranked all the way in, the knob contacts the body and flos starts just as water starts running into the comfobite mouthpiece. Std mouthpiece may be just a bit longer so gas flow may occur a little before the mouthpiece submerges.

The 1/16 of an inch difference is actually compressing the spring by that much. I still can't imagine how that could be disabled by mistake.

Hey AWAP...

I checked mine. With the valve open all the way air flows just about when the "knob" is totallly submerged. With the valve closed the air never flows.

 

[redacted]

Hey AWAP...

I checked mine. With the valve open all the way air flows just about when the "knob" is totallly submerged. With the valve closed the air never flows.

Yours could probably be tweeked a little bit but it would not be worth the trouble or expense in terms of performance to have it done. If you are a DIYer, you can keep it tuned fairly hot and handle the occasional leak (when you got too agressive) with a 1/2 turn of the adj knob.