Intermediate pressure theory/question/debate

[MR12111]

Hello . I have a question many of you have probably had already .. First just background .ex auto/truck mechanic turned scuba tech in the mid 80's ..Worked on a bunch over the years sorta got away from it when I became a Boat Captain .. Burnt out on the "business" a long time ago and am now thinking of seeing if I can enjoy being a "customer" diver ..

So anyhow going thru my gear and building my Frankenstein (dependable) reg and a question that has bugged me for years popped up again ... Intermediate pressure and the effect on air volume and cracking pressure .. I have 2 questions "theory's " 1. Higher Intermediate pressure will deliver more Volume of air ... Just seems so simple . I have always rather had the adjustment at the top of the range than the bottom of the Intermediate Pressure Range thinking it will deliver more air ...2 things wrong? with this ..Higher Pressure will hold the second stage closed more causing harder breathing ?? The pressure is what holds it closed until you crack the seal at the 2nd stage poppet .. And second ..just how much air is delivered in each breath ? will higher pressure really give you more ? I have seen the Regs. with dedicated primary ports and the bigger hoses but still only so much is needed at the second stage and to much pressure could make it breathe harder ??

Then on the other side .. I never tried this but I just might ... Use the lowest Int. Pressure you can per the specs .. My question is will this make the cracking resistance lower ? ..seems it should .. But then the lower pressure may not deliver enough air ?? If it's in specs. it should be OK ..

I have always just gone by the specs ..If the first stage has a screw adjustment ..I'd set it in the middle if the range and if it used shims I'd put back the same # of them ..Checking the Intermediate Pressure before I disassemble the Reg is important to reset it ... Hope I don't look like a total moron here ...Just curious ..the small range 15? pound of pressure range adjustment may not make any difference but I'm thinking of trying it ..

Any Help from you Old salt Reg Techs will be Appreciated .. Don


Capt Don with Divers Unlimited in Ft Lauderdale ..diving the wreck of the Mercedes ..

 

[Dsix36]

I am no expert but here is my 2 cents. Regadless of the IP, the volume is limited by the size of the smallest I.D. in the gas pathway. The pressure does not hold the second stage shut, there is a counteracting spring for that. The higher the IP, the easier it will crack (or even freeflow). I would think that with the range of the IP (and surely even under it by a safety margin) that it would supply more than sufficient volume. The cracking resistance is always set after the IP is set. if the IP goes up the cracking pressure will go down (easier to breath) and it the IP goes down the cracking pressure will go up (harder to breath).

 

[tursiops]

Here is some homework. Your ideas are not really valid.

 

[OMyMyOHellYes]

I've never failed to fill my lungs regardless of IP setting (assuming it's within spec).

I actually, like a harder draw and usually adjust regs to their most closed setting. I understand the G260s I bought were a waste of my money.

OMMOHY

 

[Jens Bölte]

Hi,

This might help
Best wishes Jens

 

[MR12111]

Thanks for all the replies ... i'm pretty embarrassed .. what was I thinking when I said the Int pressure holds the 2nd stage poppet closed ... Been a long time since I have worked on a reg .. Thanks for all the replies I will look thru it all ..

 

[MR12111]

Hi,

This might help
Best wishes Jens

Thanks for the link ..I watched it ..what I was thinking was displayed in this video ... He showed that increasing the Int. pressure will cause you to need to give more spring pressure in the second stage to seal it .... My theory is less Int. pressure would/could allow less spring pressure in the 2nd stage to seal and therefore better? breathing ... ??? Maybe ??

 

[MR12111]

I am no expert but here is my 2 cents. Regadless of the IP, the volume is limited by the size of the smallest I.D. in the gas pathway. The pressure does not hold the second stage shut, there is a counteracting spring for that. The higher the IP, the easier it will crack (or even freeflow). I would think that with the range of the IP (and surely even under it by a safety margin) that it would supply more than sufficient volume. The cracking resistance is always set after the IP is set. if the IP goes up the cracking pressure will go down (easier to breath) and it the IP goes down the cracking pressure will go up (harder to breath).

Thanks for the reply ..pretty embarrassed .. the int. pressure doesn't hold the 2nd stage poppet closed ..duh ? sorry ... This is what I was actually trying to say .. Thanks for the link ..I watched it ..what I was thinking was displayed in this video ... He showed that increasing the Int. pressure will cause you to need to give more spring pressure in the second stage to seal it .... My theory is less Int. pressure would/could allow less spring pressure in the 2nd stage to seal and therefore better? breathing ... ??? Maybe ??

 

[tursiops]

Thanks for the reply ..pretty embarrassed .. the int. pressure doesn't hold the 2nd stage poppet closed ..duh ? sorry ... This is what I was actually trying to say .. Thanks for the link ..I watched it ..what I was thinking was displayed in this video ... He showed that increasing the Int. pressure will cause you to need to give more spring pressure in the second stage to seal it .... My theory is less Int. pressure would/could allow less spring pressure in the 2nd stage to seal and therefore better? breathing ... ??? Maybe ??

No, the ease of breathing is related to the difference between the IP and the spring tension, not the absolute value of either one.

 

[The Chairman]

Regadless of the IP, the volume is limited by the size of the smallest I.D. in the gas pathway.

I'm going to disagree with my dear friend here: Your tidal volume limits the volume of air. The IP and orifices may govern the rate of flow once the diaphragm is fully depressed. The second stage poppet adjustment makes or breaks the breathing experience for most. However, a too high IP may cause people to feel that air is being rammed down their throats. Too light, and you might be able to over breathe your reg when deep.