Strange IP behavior on a freshly serviced regulator - what's going on?

[Scuba-74]

I just had one of my regs serviced by a professional technician, and now it exhibits very strange behavior:

1. When put on a tank and pressurized (before cycling) - IP goes all the way to 170 and stays there.
2. When cycled by purging or breathing, IP drops to 135-ish, and from that point forward everything looks good - IP drops and recovers quickly with each cycle, no creep.
3. When tank valve is closed, reg de-pressurized, and valve reopen - IP goes back to 170, see #1.

I thought I may have a bad IP gauge (mine is cheap), but fancy hookup with a large professional gauge at the LDS showed same thing. They said they'll look into it.

So I have a couple of questions. First, what is going on? It appears that after the first breath the reg works to the specs. What is there that keeps IP high before the first breath? I doubt that it is normal with any reg. If it is, I'll gladly stay corrected.

Second, and it's a difficult one to ask. Would a qualified technician let a reg leave his bench with this type of behavior? And if not, what does it tell me? Was the service done, but the IP wasn't tested? That seems unlikely. Was the service not done?

 

[John Bantin]

It sounds like something is blocking the air flow. You can replicate this effect with a fully functioning regulator by partially opening the tank valve.

 

[happy-diver]

From early teens to closer to death, my regs have never seen the inside of a dive shop

 

[lexvil]

Diaphragm or piston?

 

[stepfen]

I had the same question some time ago and I was told by the gurus here that what you describe is normal. There is some inertia in the way the inner parts of the regulators work hence when gas is supplied to the reg for the first time it takes some extra time for the reg to lock and as a result the ip climbs a bit higher than "normal". From that moment on any breath/purges cause relatively small pressure changes hence the reg has enough time to lock the ip where it should be.

I don't know if 170 is too much or if there is "too much" for this. Maybe somebody like @couv or @rsingler can comment.

BTW opening the valve slowly reduces this quite a bit. In my case (Mk11 diaphragm reg), it goes up to ~160 (11bar) if I open the valve fast, but I've got the habit of opening the valve slow now and it goes to something like ~150 or less.

It's a mistake that beginners like me often do: pressurize their regs (without breath/purge it), see an increased (but stable) IP and adjust it based on this to end up after a couple of breathes with too low IP. Always breath/purge the reg several times before you measure the IP!

 

[The Chairman]

It could be internal sticking or the HP seat not being broken in.

However, if you're not holding in your purge as you pressurize your tank, you're doing it poorly. No, not wrong, but you're slamming that knife edge into the seal at 3,000 psi. Holding the purge softens this initial blow considerably. Try that and tell us what the initial IP sits at when you do. I bet it will be normal.

 

[Scuba-74]

Diaphragm or piston?

Balanced diaphragm.

 

[Joneill]

It could be internal sticking or the HP seat not being broken in.

However, if you're not holding in your purge as you pressurize your tank, you're doing it poorly. No, not wrong, but you're slamming that knife edge into the seal at 3,000 psi. Holding the purge softens this initial blow considerably. Try that and tell us what the initial IP sits at when you do. I bet it will be normal.

Interesting- do you do that when opening a tank pre-dive or just when checking IP?

 

[lexvil]

Balanced diaphragm.

That was my assumption. I have seen this with aqualung type where I suspect the seat but when I lowered the IP to 120 it was ok for a few months and started it again. They need to service it again if it won’t seat properly.

 

[broncobowsher]

What happens if you slowly crack open the tank?