Question IP - when is high too high?

[DecoBrad]

I have a question regarding IP. When is high too high. Let me elaborate.

A constant IP is a significant determinant of second-stage behaviour, I get that part. Set an IP (9,5 bar say), set the second stage correctly and all is well. Now, let's say that you intentionally increase the IP to 10 bar, and re-set the second stage (assuming the correct lever height, appropriate spring tension etc). The regulator will function. Is there a down-side of running a higher than conventional IP if the second stage is set for it?

The context of this question is that most manufacturers specify an IP between 9-10 Bar. There may be no need to go higher, sure. But my question is whether there is a technical challenge/concern or performance penalty for going higher?

 

[halocline]

I have a question regarding IP. When is high too high. Let me elaborate.

A constant IP is a significant determinant of second-stage behaviour, I get that part. Set an IP (9,5 bar say), set the second stage correctly and all is well. Now, let's say that you intentionally increase the IP to 10 bar, and re-set the second stage (assuming the correct lever height, appropriate spring tension etc). The regulator will function. Is there a down-side of running a higher than conventional IP if the second stage is set for it?

The context of this question is that most manufacturers specify an IP between 9-10 Bar. There may be no need to go higher, sure. But my question is whether there is a technical challenge/concern or performance penalty for going higher?

As long as the IP is stable, running it on the high side of factory specs should be fine. If anything, you’ll have a performance increase as there would be theoretically higher flow to the 2nd stage.

The one theoretical downside I can think of is if you have an unbalanced 2nd stage, you will need to set the spring a little tighter to compensate, which means more pressure on the seat during storage. That could result in more wear.

I tend to set my IP on the low side for more practical reasons. One, I use very high quality 2nd stages that easily tolerate lower IP, and I find there’s a little less tendency to free flow, like when switching 2nd stages during a dive. Two, IP in the first stage never goes down over time, always up as the HP seat wears. So starting with low IP tends to make the HP seat last longer; there’s less seating force on the seat itself, and there’s more room to tolerate a gradual increase in IP over time.

 

[lexvil]

I don’t go to bars but…steady is good, excessive is not good. To high will lead to unexpected spewing.

Most specs are 135 to 145 psi, which I believe is close to 9 to 10 bar, I’ve started to run mine at the upper end because that is how most of my new regs have come from the factory so I just go with it.

As with most bars, creep is bad.

 

[Johnoly]

... Is there a down-side of running a higher than conventional IP ....

Is there an "up-side" that you are looking to get ??

 

[Nemrod]

It depends upon the specific regulator. The spring at the diaphragm or piston maybe beyond it's operating range and begin to become coil bound. An unbalanced second stage will require higher seat tension to seal against the out of spec high IP. The overall reliability of the regulator will be reduced and wear possibly increased depending upon the particular component. Stay within the specified IP if to the high side and be happy.

 

[Eric Sedletzky]

I think running IP on the lower side is better. More stable and less freaky free flows. Plus on an unbalanced 1st and 2nd like a MK2/R190 it starts breathing hard at less tank pressure, otherwise at high IP the spring in the second is too tight and starts to close out too early.
I don’t dive deep so no need to hot rod my regs.
I’m happy with 120 to 135.

 

[rsingler]

The one advantage to a higher IP is with unbalanced second stages, like much of the Mares line that doesn't say "ADJ" (adjustable). For Mares, standard IP is 142-148 psi (10 Bar), where most others are 125-145 psi (8.5-10 Bar).
In an unbalanced second, it is much easier to get smooth operation with a higher IP, because the balance of downstream force on the seat versus spring counterforce is easier to achieve. With a lower IP, you have to back off on spring pressure, and while we'd like to believe that spring constant is linear, it isn't.
But for the 80% of the world that is an end-balanced barrel design second, it doesn't much matter, within spec.

 

[Nemrod]

The one advantage to a higher IP is with unbalanced second stages, like much of the Mares line that doesn't say "ADJ" (adjustable). For Mares, standard IP is 142-148 psi (10 Bar), where most others are 125-145 psi (8.5-10 Bar).
In an unbalanced second, it is much easier to get smooth operation with a higher IP, because the balance of downstream force on the seat versus spring counterforce is easier to achieve. With a lower IP, you have to back off on spring pressure, and while we'd like to believe that spring constant is linear, it isn't.
But for the 80% of the world that is an end-balanced barrel design second, it doesn't much matter, within spec.

Exactly, a pneumatically balanced second stage, of which the most copied design is the storied G250/G260 type, the IP does not especially matter as long as it is in specification. I sometimes use my new favorite first stage, a simple, ultra reliable SP Mark 2 Evo and it being an unbalanced piston has a variable IP from full to empty. And fitted with two well tuned balanced G250 seconds, it does not matter as they hardly notice a difference in the IP nor do I breathing from them until somewhere well south of 500 psi, like in olden times, I can feel a slightly increasing draw.

 

[DecoBrad]

As long as the IP is stable, running it on the high side of factory specs should be fine. If anything, you’ll have a performance increase as there would be theoretically higher flow to the 2nd stage.

The one theoretical downside I can think of is if you have an unbalanced 2nd stage, you will need to set the spring a little tighter to compensate, which means more pressure on the seat during storage. That could result in more wear.

I tend to set my IP on the low side for more practical reasons. One, I use very high quality 2nd stages that easily tolerate lower IP, and I find there’s a little less tendency to free flow, like when switching 2nd stages during a dive. Two, IP in the first stage never goes down over time, always up as the HP seat wears. So starting with low IP tends to make the HP seat last longer; there’s less seating force on the seat itself, and there’s more room to tolerate a gradual increase in IP over time.

That makes complete sense! So do you run closer to 9 bar for IP?

 

[TrimixToo]

When is the IP too high?

- When the O-rings blow
- When the hose to the 2nd stage explodes
- When the 2nd stage won't stop flowing until the valve seat is so tight it won't open at all
- When the lever bends before opening the 2nd stage valve
- When your cheeks go hollow trying to take a breath even though the tank is full
- When you take a breath and suddenly look like the Stay Puft Marshmallow Man!

Sorry. Don't know what got into me. (Not. Yes, I do.)

More seriously, I'd want to not increase the pressure of the 2nd stage valve seat arbitrarily. Not because I'm a regulator design expert of any sort, but because common sense tells me the experts think it will work best in the range of pressure specified as the IP and I don't have the knowledge to disagree with their assessment.