Understanding Intermediate Pressure

[WhiteSands]

Hi,
I'm reading Reg Saavy and need some help understanding IP.

My understanding of IP is this:

It is the pressure supplied into the first stage (from the tank) which is sufficient to overcome spring & water pressure so that the hard and soft seats first make contact and and forms an air-tight seal.

Is this a correct understanding of what IP is?

 

[Agility]

IP is the pressure the first stage delivers to second stage or inflator through the IP or LP ports. IP and LP are synonymous.

 

[lemke]

Not exactly... Keep in mind each stage has TWO chambers... a high pressure (input) side, and a low pressure (output) side. IP is the OUTPUT pressure from the first stage (which becomes the INPUT pressure for the second stage).

What you described above is the SUPPLY pressure.

 

[axxel57]

The tank pressure is the High pressure (HP), at full tank usually 3000psi - 207bar.

The only thing a 1st stage has to do is to reduce this HP to an Intermediate Pressure (IP or also LP for Low Pressure) which is usually around 140psi - 9,5bar.

If the 1st stage can produce this IP stable (0-10psi max difference) regardless the decreasing tank pressure during a dive,the 1st stage is balanced.

If the IP is increasing or decreasing more than 13 - 25psi between full and near empty tank, the 1st stage is probably an unbalanced 1st stage (exceptions MK11 & MK17:cool2.

 

[redacted]

Hi,
I'm reading Reg Saavy and need some help understanding IP.

My understanding of IP is this:

It is the pressure supplied into the first stage (from the tank) which is sufficient to overcome spring & water pressure so that the hard and soft seats first make contact and and forms an air-tight seal.

Is this a correct understanding of what IP is?

Reg Savvy has a few pages dedicated to definitions of various "pressure" related terms. How did you read that and come up with your definition??

 

[AevnsGrandpa]

So to jump in on this with a question, what is a better 2nd stage reg...? One that suppies you the same pressure till you are pretty much out or one that reduces as the tank does? I see advantages with each...But good explination.

Jeff

 

[lemke]

The second stage can only use what the first stage outputs... IP. An upstream first stage (diaphragm) will tend to increase the IP as the supply pressure drops (easier to breath). A downstream first stage (piston) will tend to decrease the IP as the supply pressure drops (harder to breath). This is the "nutshell" explanation as there are many variations to the basic upstream/downstream design per manufacturer.

 

[halocline]

Hi,
I'm reading Reg Saavy and need some help understanding IP.

My understanding of IP is this:

It is the pressure supplied into the first stage (from the tank) which is sufficient to overcome spring & water pressure so that the hard and soft seats first make contact and and forms an air-tight seal.

Is this a correct understanding of what IP is?

IP is the pressure required to close the 1st stage valve. It is working against the mainspring and ambient pressure to do that, so in that sense your statement is absolutely true.

But the pressure supplied to the first stage is tank pressure or, simply, supply pressure. I suspect you realize this. This pressure builds up in the IP chamber of the 1st stage, closing the valve and cutting off the supply. So the first stage is what's called a 'regulating' valve. Then when you take a breath, you lower the pressure in the IP chamber by drawing air from it, which opens the valve a bit, letting air in, until it builds back up to IP and then closes.

The Vance Harlow book has some good simple diagrams that illustrate this very clearly. Sometimes I think regulator savvy is not the best -written book in the world, although it does have lots of detailed information.

---------- Post added June 4th, 2014 at 01:58 PM ----------

So to jump in on this with a question, what is a better 2nd stage reg...? One that suppies you the same pressure till you are pretty much out or one that reduces as the tank does? I see advantages with each...But good explination.

Jeff

You probably mean "what is a better 1st stage", right? Because the 2nd stage doesn't supply any pressure except ambient, and they all do that until the tank is empty.

Assuming you meant 1st stage, most folks that understand how these things work would say that theoretically, a balanced 1st stage is overall a better option, which is what supplies you with stable IP throughout the supply range. However, there are some good performing unbalanced 1st stages as well. The balanced design has fewer limits on overall flow rate and helps unbalanced 2nds to perform quite well, but there are lots of factors.

 

[divad]

The Vance Harlow book has some good simple diagrams that illustrate this very clearly.

Yeah, the compressor analogy is great.

 

[Mikko Ilari Laakkonen]

If the IP is increasing or decreasing more than 13 - 25psi between full and near empty tank, the 1st stage is probably an unbalanced 1st stage (exceptions MK11 & MK17:cool2.

What? MK11 and 17 are both balanced and have a steady IP.