Question IP Too High, so what? and why?

[phgachoud]

Starting servicing 1st stages, it seems that IP too high is a pretty common simptom, I was wondering

1. Why does that happen with time? Not sure it does on pistons but seems to be the case. Does the spring loose elasticity? If so IP Should go down with time as far as I understand.
2. And what is the behavior of a too high IP first stage, and too low, workaround will be to close the second stage's free-flow screw (as long as you can) till it doesn't freeflow anymore. What happens in different depths (I mean physics) and what are the dangers of that?

Not here to argue with constructors values which I anyway trust but trying to understand the consequences of a reg not being checked for IP out of range.

Live in Chile we have many dive centers (and probably people) who dont care about regs maintenance as long as they breath on surface... it breathes, it works, dont touch them but that's not the topic...

Thx!

 

[tbone1004]

1-typically it will start doing something called "creeping" where air is able to bypass the seat and it leaks. This happens in all first stage designs.
2-too high will cause the second stage to freeflow, too low will cause it to breathe really stiff, though I personally haven't seen one with too low of an IP before. Not to say it won't/can't happen, but it's extremely unlikely.

 

[James79]

Why does that happen with time? Not sure it does on pistons but seems to be the case. Does the spring loose elasticity? If so IP Should go down with time as far as I understand.

First stages (whether piston or diaphragm) are essentially held open by spring pressure and closed by IP exceeding the set spring pressure. With use, the soft seat can slowly take a set, resulting in the spring having to compress a tiny bit further to seal and a corresponding higher IP. If it's just wear in causing it, it will be a stable higher IP and just need to retune the second to match (as long as it doesn't go outside the limits of what the second can do).
If the IP isn't just a little high, but continues to rise (stopped only by the second stage freeflowing), it is IP creep (as @tbone1004 mentioned) and needs to be rebuilt to address the cause.

Just my self taught 2 cents,

James

 

[350xfire]

Depending on how much time between service intervals you are referring to, a good initial break-in may help to minimize the IP increase over time.

 

[phgachoud]

@350xfire could you explain a bit more please?

Depending on how much time between service intervals you are referring to, a good initial break-in may help to minimize the IP increase over time.

 

[350xfire]

@350xfire could you explain a bit more please?

When you service a reg you should cycle it quite a few times to get the seats to break in. This wears a nice circle groove into the seats. Scubatools sells a fixture to do this but most people do without.

Quick Set - Poppet & Seat Break-In Fixture

The Scuba Tools "Quick Set" fixture is designed to quickly and efficiently "break-in" new poppets and HP seats.When a new poppet or HP seat is installed in a regulator, it may not perform correctly until a mating groove has been set in the soft side of the seat. This initial groove is...

www.scubatools.com

For the home user it can be done by pressing and depressing the purge many times. For someone who services regs for customers, it is a worthwhile tool since it can help break in a newly serviced reg in about 5 minutes.

 

[halocline]

Starting servicing 1st stages, it seems that IP too high is a pretty common simptom, I was wondering

1. Why does that happen with time?

I'm not sure from your post if you understand that the job of a 1st stage is to lower the tank pressure to IP and send that pressure to the 2nd stage. (sorry if that's obvious to you) There are two chambers in every 1st stage, one that has HP air from the tank, one that has air at IP. There's a valve that seals these chambers off from each other, opening and closing depending on the pressure that is in the IP chamber. It's the air pressure in the IP chamber that forces the valve closed. This valve will begin to leak over time, usually due to wear in the seat. When that happens, HP air from the tank begins to leak into the IP chamber, and that's when it's time to rebuild, which includes replacing the worn seat.

The early stages of wear usually just mean that the valve is a little harder to close tightly enough to not leak, which means that the IP (which is the force closing the valve) will be higher. As the wear gets worse, air will continue to leak past the valve and force the 2nd stage to free flow.

 

[350xfire]

I'm not sure from your post if you understand that the job of a 1st stage is to lower the tank pressure to IP and send that pressure to the 2nd stage. (sorry if that's obvious to you) There are two chambers in every 1st stage, one that has HP air from the tank, one that has air at IP. There's a valve that seals these chambers off from each other, opening and closing depending on the pressure that is in the IP chamber. It's the air pressure in the IP chamber that forces the valve closed. This valve will begin to leak over time, usually due to wear in the seat. When that happens, HP air from the tank begins to leak into the IP chamber, and that's when it's time to rebuild, which includes replacing the worn seat.

The early stages of wear usually just mean that the valve is a little harder to close tightly enough to not leak, which means that the IP (which is the force closing the valve) will be higher. As the wear gets worse, air will continue to leak past the valve and force the 2nd stage to free flow.

Yes, I understand the concept.... This is why I said "depending on how much time between service intervals" on my first post.... If the IP is increasing within a month after service, the regulator was probably not broken in properly...
Now, if this is 2 years and 150 dives after, then I agree, service it and place new parts in it because the seats are just plain work out...

I have recently serviced a couple of regulators that were serviced less than a year before I got them and barely dived with... The IPs were over 150psi almost 160psi. I don't think any technician worth a crap would have let those go out of their service center with that high of an IP... So my only conclusion is that they set everything properly (hopefully) but didn't perform any break in procedure. After the reg was used a while parts broke in and IP increased.

The original post does not talk about "creep" just increasing IP over time...

 

[halocline]

Yes, I understand the concept.... This is why I said "depending on how much time between service intervals" on my first post.... If the IP is increasing within a month after service, the regulator was probably not broken in properly...
Now, if this is 2 years and 150 dives after, then I agree, service it and place new parts in it because the seats are just plain work out...

I have recently serviced a couple of regulators that were serviced less than a year before I got them and barely dived with... The IPs were over 150psi almost 160psi. I don't think any technician worth a crap would have let those go out of their service center with that high of an IP... So my only conclusion is that they set everything properly (hopefully) but didn't perform any break in procedure. After the reg was used a while parts broke in and IP increased.

The original post does not talk about "creep" just increasing IP over time...

I wasn't replying to you, I'm not sure if that was clear. I'm sure you understand how regulators work. Regarding your break in procedure, I certainly agree that regulators should be cycled multiple times after service to help the seats settle in, but this is more for the 2nd stage seat than the 1st stage. It's the softer 2nd stage seat that usually needs to be broken in a bit so that the technician can then set the cracking effort accurately. Most 1st stages, at least ones that I've worked on, hold IP accurately right from the start. Maybe they don't lock up perfectly for the first few seconds, but then they're fine.

Another thing I routinely do when servicing 1st stages is to leave them pressurized for an hour or so, usually with the tank valve off. Then I check both tank pressure and IP and confirm that neither has moved. This tells me there are no slow leaks or slow IP creep.

 

[Subcooled]

Starting servicing 1st stages, it seems that IP too high is a pretty common simptom, I was wondering

1. Why does that happen with time?

The seal is made by rubber.
It does not live forever.
It will wear out.
Leaks will form.
Hence, IP grows.

That's why regular servicing is required - to replace the rubber!