Primary IP clarification

[trymixdiver]

possibly a dumb question, but i want some clarification on Primary regs IP. Am i correct or do i have it mixed up with the backups IP.

Adjust the intermediate pressure of the first stage, but keep it as low as you can??

Is this correct or should it be highier to improve its performance at depth? or am i confusing it with the backup reg.



Andy

 

[Lost Yooper]

With mix, you can keep them tuned down and still have good breathers.

Mike

 

[The Chairman]

Hey Andy,

The intermediate pressure is adjusted on the first stage and so is the same for both primary and backup second stages. Each manufacturer gives us a range within which the first stage should be able to operate. Some like to "detune" their regs (use lower than optimal pressures) while some like to push it to the limit and then some. This is a personal preference and one that it is best to experiment with a little at a time. Too much IP and you will have free flows out the wazoo. Too little and breathing effort can increase dramatically. Since I dive only air and NitrOx I like to set my regs within 2% of the max allowable. Since I fine tune my regs after the O-Rings set, I have had no problems with this at all. Of course, living in a sub tropical evironment has it's advantages.

 

[neil]

There is no compelling reason to use IP other than the range the manufacturer suggests, and that includes their suggestions for cold water. Too high and you may get free flows. Too low and you get reduced performance. If you want to minimize the possibility of a freeflow on a backup, the adjustment is made at the second stage. As a general rule, the higher range of acceptable IP will give better performance.
It is also a misconception that higher IP causes the HP seat to wear faster. The closing force on a balanced reg's seat is unaffected by IP.

I am not an engineer or an expert in fluid dynamics, but I think I got all that right.

Neil

 

[The Chairman]

Vance Harlow's Regulator Maintenance and Repair.

IP is set on the first stage. This is usually done with shims or by allen wrench.

Cracking pressure is then set on both of the second stages. Yes it is customary to set the cracking pressure for the backup a tad on the "high" side, so it won't bubble or free flow.

 

[roakey]

Originally posted by NetDoc
The intermediate pressure is adjusted on the first stage and so is the same for both primary and backup second stages

In anything but the technical section I would have said the same thing, however, since this question is in the technical section I'm assuming two first stages so you *could* set them differently.

That said, all IPs should be the same just for simplicity and in case you want to do the full nine DIR yards and move second stages around during the dive in the event of a second-stage failure.

Roak

 

[Stone]

Originally posted by NetDoc
May I recommend...Vance Harlow's Regulator Maintenance and Repair.

I think Pete and I ought to ask Mr Harlow for a commission on the sales of his book generated on scubaboard .

 

[roakey]

Originally posted by Stone
I think Pete and I ought to ask Mr Harlow for a commission on the sales of his book generated on scubaboard .

Get in line behind me for the Oxygen Hacker's Companion

I've been recommending it for years on Diverlink and before that Rodales since '99. The first testimonial on http://www.airspeedpress.com/newoxyhacker.html has been up there for years, guess who R.O. is?

Roak (aka Roger Oakey )