IP Gauge Reading

[Dan]

Mk 25 specification: 125-145 psi at both 300 and 3000 psi tank pressure, with no creep.
(IP will be a little different at the two extremes, but must fall within that range)
So "in the green" is probably too high for that gauge. But the key is no creep, as you stated. You can use just about any IP you like with the balanced S600. But having said that, I've once seen a linear crack in the S-wing poppet in a reg set that came with a first stage whose IP was way above spec.

Thanks for the info. I’ll definitely check mine in the next trip.

 

[stuartv]

Mk 25 specification: 125-145 psi at both 300 and 3000 psi tank pressure, with no creep.

What I was told in class on Wed is the Mk25 spec is 145psi with a 500 psi supply. It will be lower with a 3000psi supply, but there is no spec for exactly how much lower.

 

[rsingler]

What I was told in class on Wed is the Mk25 spec is 145psi with a 500 psi supply. It will be lower with a 3000psi supply, but there is no spec for exactly how much lower.

My info was from the service manual. Rene Dupré from SP has off the record add'l comments in Service Seminars, like "an IP drift of up to 8 psi in the first minute with a new seat is acceptable as it breaks in, as long as it locks up within spec."
But anywhere between 125 and 145 is an acceptable IP. What is important is, 1) that it's consistent week to week, and 2) that there's no creep. That's all.
Ice divers like low IP's. Some warm water divers like lower IP's, so that even if there's a tiny bit of creep, the reg won't start to freeflow. Stating specifically "145 @ 500" is just one person's opinion. It may drop a few psi with a full tank by design (differential piston diameters at shaft and knife edge). But with their balanced seconds, any IP in the stated range is acceptable.

 

[stuartv]

My info was from the service manual. Rene Dupré from SP has off the record add'l comments in Service Seminars, like "an IP drift of up to 8 psi in the first minute with a new seat is acceptable as it breaks in, as long as it locks up within spec."
But anywhere between 125 and 145 is an acceptable IP. What is important is, 1) that it's consistent week to week, and 2) that there's no creep. That's all.
Ice divers like low IP's. Some warm water divers like lower IP's, so that even if there's a tiny bit of creep, the reg won't start to freeflow. Stating specifically "145 @ 500" is just one person's opinion. It may drop a few psi with a full tank by design (differential piston diameters at shaft and knife edge). But with their balanced seconds, any IP in the stated range is acceptable.

For completeness sake, my clinic was with Rene.

And I'm not saying (AT ALL) that you are incorrect. I'm just saying that what Rene told us is that the spec for a Mk25 is IP of 145 with a supply pressure of 500. And, yes, he explained the same thing about the piston shaft and why the IP drops at higher supply pressures.

If I'm working on a reg, I would rather have a specific number as a target and then a tolerance range - rather than just a range with no specific target. The Mk25 IP is easy enough to adjust, so getting it to 145 (+/- 0.5) is not hard.

Question: Why would a lower IP make it less likely to freeflow? It seems like if you tune the cracking pressure the same, a 5psi creep on 140psi would be more likely to cause freeflow than 5psi creep on 145. Is creep going to be the same percentage (rather than same absolute #)? So, if it creeps 5psi on 140, then it would creep a bit more than 5psi when starting from 145?

 

[rsingler]

For completeness sake, my clinic was with Rene.

And I'm not saying (AT ALL) that you are incorrect. I'm just saying that what Rene told us is that the spec for a Mk25 is IP of 145 with a supply pressure of 500. And, yes, he explained the same thing about the piston shaft and why the IP drops at higher supply pressures.

If I'm working on a reg, I would rather have a specific number as a target and then a tolerance range - rather than just a range with no specific target. The Mk25 IP is easy enough to adjust, so getting it to 145 (+/- 0.5) is not hard.

Question: Why would a lower IP make it less likely to freeflow? It seems like if you tune the cracking pressure the same, a 5psi creep on 140psi would be more likely to cause freeflow than 5psi creep on 145. Is creep going to be the same percentage (rather than same absolute #)? So, if it creeps 5psi on 140, then it would creep a bit more than 5psi when starting from 145?

Downstream second stages are sensitive to increased IP. Balanced seconds, not so much. So if you tune to a light cracking effort at a given IP, and the IP rises 10psi, your second may begin to gently bubble.
The added air pressure against the seat forces a downstream valve open. The amount of that force is psi x orifice area.

Ex: 130 psi x 4mm orifice = ~2.6#
140 psi = ~2.8#. The extra .2 lbs of force may be enough to open the valve against your set spring pressure.

But yes, I agree with what you said - there's no reason, at any set cracking effort (for that IP) for a second stage to freeflow at higher IPs than lower. They key is tuning your second to your first.

 

[Umuntu]

If I'm working on a reg, I would rather have a specific number as a target and then a tolerance range - rather than just a range with no specific target. The Mk25 IP is easy enough to adjust, so getting it to 145 (+/- 0.5) is not hard.

I generally see the mid-point of a range as the target.

 

[stuartv]

Downstream second stages are sensitive to increased IP. Balanced seconds, not so much. So if you tune to a light cracking effort at a given IP, and the IP rises 10psi, your second may begin to gently bubble.
The added air pressure against the seat forces a downstream valve open. The amount of that force is psi x orifice area.

Ex: 130 psi x 4mm orifice = ~2.6#
140 psi = ~2.8#. The extra .2 lbs of force may be enough to open the valve against your set spring pressure.

But yes, I agree with what you said - there's no reason, at any set cracking effort (for that IP) for a second stage to freeflow at higher IPs than lower. They key is tuning your second to your first.

Thank you. Your posts have been really educational. Not just in this thread, but others I have been reading that were not specifically addressed to me.

I appreciate you taking the time to try to educate me!

I generally see the mid-point of a range as the target.

Me, too. Thus, with the range rsingler mentioned of 125 - 145, I would be aiming for 135. When the spec (communicated to me) is actually 145. Being told "125 - 145, but aim for 145" seems better to me than just "125 - 145".

Rene also told us that their unbalanced 2nd stages are generally set to blow off if the IP hits 165. So, the target is 145, but erring on the low side is preferable.

 

[Fibonacci]

I'm unexpectedly in the market for a new IP gauge, 2" or 2.5" face, 0-300psi, 5spi increments, 1/8" NPT bottom connection, liquid dampened to replace one on my undampened SCUBA Tools IP tool that bent the needle against the stop when I carelessly vented the residual pressure in one step. Lesson learned

SO... any recommendations for an accurate dampened gauge gratefully received!
I see plenty on eBay but is it worth getting something like a Winters gauge that has an accuracy calibration and a 5 years warranty?

 

[tbone1004]

any industrial gauge supplier should be able to hook you up. Not sure what's available in Oz, but literally any gauge will work. The 300psi ones MAY be 1/4" NPT only, but you can go to your equivalent of Lowes/HomeDepot and get a 1/4npt to 1/8npt reducer. I have one on my big IP gauge because the large diameters were only available in 1/4

 

[Fibonacci]

When I first got the Scubatools IP gauge I compared it to three other gauges, all were different!
Scubatools one was supposedly recalibrated for 100-150psi zone... but not fluid filled and easily damaged as I discovered

An IP gauge is a test instrument so I was trying to find a more accurate replacement... liquid filled 0-300psi gauge with 2-1-2% specification, where the 1% accuracy is in the middle of its range around 150psi.
Should really have a calibration certificate.

These are not so easy to find in Australia or even in the US it seems...