help explain what LDS shop reported about my second stage?

[Thalassamania]

148 and stable would not worry me in the least. In fact, if the intermediate pressure is not blowing my second stage open and my second stage is easy to crack ... I'd be happy. I've often had to adjust my IP in the field and not had an IP gauge, so I slowly turn the pressure up until I get free flow, back it off a bit, advance it a hair breathe, advance it a hair, breathe, and keep on going until I fell like it's pushing too much air at me, then I back it off a tiny bit and call it a day. IP creep is the killer, when that happens you know that something's wrong and you need to change out some parts (at least).

 

[fisheater]

What is the usual cause(s) of IP creep?


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[Thalassamania]

Bad HP seat or knife edge.

 

[herman]

Or defective Oring in a diaphragm reg.

 

[halocline]

My understanding is that the acceptable range is 140 -- 150, and the usual target range is 145. So 148 is close.

I agree that if the target was 135, then 148 would be alarming. But I think it was supposed to be set to 145 -- that's what the tech guy said they're generally set to.

To answer your earlier question, when they said "pressure at the 2nd stage" they actually meant the pressure that the 1st stage is dropping tank pressure to and sending to the 2nd stage. Lots of people have already mentioned something like that, I just wanted to make sure you understood why they said "2nd stage pressure."

You can find out what the typical IP for this regulator is, but you should understand that the IP gauges used by most of us are hardly calibration-standard. So you really don't know if its actually 148, or maybe 143, maybe 152...unless you check with either a much more accurate gauge or get a good idea by trying a few different gauges.

For most modern, balanced 1st stages, 148 (if it's really that) is a little high IMO. But, for an unbalanced piston 1st stage on a full tank, it's about right. As several people have mentioned, IP stability is much more important and indicative of 1st stage health than the specific IP it's set to. 1st stages' primary job is to step the very high (and variable) tank pressure down to a stable IP; so one of the most common signs of 1st stage trouble is the IP "creeping" up; you can see the gauge slowly rising while the reg is pressurized and the 2nd stage is closed. It's basically a slow leak inside the 1st stage, usually at the main valve (hp seat) but sometimes at the tiny o-ring that seals the balance chamber common to balanced diaphragm 1st stages. That's what Herman was mentioning.

When I rebuild my own regs, which are mostly balanced piston, I set them much lower; 125 PSI. There is a theoretical advantage to this and a disadvantage; the advantage is that IP rarely goes down as the seat wears; almost always up, and setting them low gives me lots of room before I need to rebuild. The disadvantage is that the flow to the 2nd stage is lower; but since my 1st stages flow plenty of air, I don't worry about it. Assuming your 1st stage is a fairly typical balanced diaphragm, 148 sounds pretty high, although you didn't mention what the supply pressure was when they checked. Even though all (I think) modern diaphragm 1st stages are balanced, its possible that there is a slight rise in IP as the tank empties. So, if 148 was with a near-empty tank, they might measure it with a full tank and get something in the low 140s or even lower.

If you're really interested in this topic, even after reading this thread , you can get Vance Harlow's fine book on regulator repair and you'll find an excellent, easy-to-read explanation.

 

[captain]

The reason there is a specification range is because it will work properly if within that range. If you had an IP gauge on your regulator to see the IP every time you turned it on it would probably vary some amount within that range. As Herman says it is more important what it does than what it is as long as it in the range.

 

[Zung]

It's a balanced piston 1st stage, and the official service manual says:

Correct intermediate pressure for the first stage is between 135-145 psi, with a supply pressure of 2,500 - 3000 psi.

So the average is 140, and 148 PSI is not too bad; it's just that most of us are used to seeing 135 which is sort of an industry standard, but any manufacturer/vendor is free to specify whatever they want within reasonable limits.

Btw, the internals of this reg look nice.

 

[Dauntless]

Had LP port pressures in 140's and kept blowing inflator valves and had leaking into BC until had technician put in a shim to decrease to 130's - no problems after.

 

[LeadTurn_SD]

Had LP port pressures in 140's and kept blowing inflator valves and had leaking into BC until had technician put in a shim to decrease to 130's - no problems after.

That surprises me. First, that the inflator valve would leak at such a low IP (Mares diaphragm regs are spec'ed in the 140's as normal IP).

Second, that the inflator would "let go" before excess pressure was vented by the 2nd stage. My experience has been that the 2nd stage (if the 2nd is a downstream design.... most are) will freeflow before the inflator leaks... I've read about certain exceptions, but think this is uncommon?

Could it have actually been much higher than 140?? What regulator?

Best wishes.

 

[Shftrdog]

Ok the 148 in the intermedite pressure and it should be anywhere around 135 to 145. 148 is not bad and all they had to do is tune it down a little bit. You should get it overhauled every year or every 50 dives but should only pay around $40 per stage including parts. As long as the intermedite pressure was not increasing all the dive shop had to do was tune it down.