Re-Retune IP - Legend LX ACD Supreme

[Chewie07]

I had purchased an Legend LX ACD Supreme back in September and I had it retuned to an IP of 150. I wasn't planning on diving ice/cold water back then.

But, it has performed flawless nonetheless.

Now, I will be starting to dive colder water including cave dives, ice dives, etc (our certification for the dives start in September). But I will also continue to use it in 50 - 60 degree water throughout the summer as well.

Do I need to have my LDS re-retune the IP back down to 135 or is it fine where it is? Would you all recommended that I put the IP back to the factory settings? Will this have a negative impact on warmer water diving?

Thanks for the help!

P.S. I got the recommendation to raise the IP from some of the LX Supreme threads here... Just to show off my lack of IP knowledge. What REALLY is the difference between an IP of 135 & 150. I understand the 135 is required for colder water?

 

[furtif]

123±7 psi Legend LX ACD Supreme


Jean-François Blard

 

[DA Aquamaster]

The flow rate at an IP of 150 psi will be about 11% more than it is at 135 psi. Given that the legend first stage and second stage already have enough flow rate, increasing the IP to boost the flow rate is pretty much a waste of time.

The idea behind a lower IP is that it will reduce the flow rate and (slightly) reduce the adibatic cooling that might result if, for example, the second stage falls out of your mouth and freeflows. If a 10% to 15% difference makes a difference, you need a better cold water reg.

All that said, I'd have it readjusted to the middle of the factory spec of 135 psi.

I have no idea where the above mentioned 123 psi +/- 7 psi came from. My service manual states 135 psi +/- 5 psi with a maximum of 5 psi of creep allowed. With an adjustable spring pad as found on the Legend, there is no reason it cannot be set to exactly 135 psi.

 

[weaserm99]

The 123 psi +/- 7 is actually what the legend supreme models are set for, that is the only difference between the normal legend and the supreme model, other than cosmetic. Thats why when i had a regular legend i set the IP to 125.

Dip'N Dive - Scuba Diving Training in Buffalo and WNY - Home

 

[tfsails]

Jacking the IP messes with the second stage's adjustment more than it affects the first stage. A standard downstream second stage has to overcome the intermediate pressure with spring force to prevent free flow. If you jack up the IP then the spring has to overcome more air pressure in order for the second stage to seal up when not being inhaled from. The reg would breathe too easily, and be too susceptible to free flow.

I see no advantage at all to jacking up your IP beyond what is called for in the book. It could also void your warranty if the wrong people heard about your doing it. I've never heard of this happening, but these days anything is possible.

 

[Chewie07]

Sounds great! Thanks for all the information. I will certainly have it set back to 135 and leave it there permanently.

I still can't find the 123 +/- 7 anywhere either (the link didn't help me). I have copies of the 1st & 2nd stage service manuals an dthey both indicate 135 +/- 5 as the correct Mechanical Pressure (is that the same as IP)?

 

[tfsails]

I just looked at the Legend 1st stage service manual and it calls for a "medium pressure" (MP) of 135psi which is the same thing as "intermediate pressure". It is the output pressure of the first stage which is sent to the second stage where it is ultimately breathed.

I did not see any tolerance but + - 5psi is well within normal tolerances for just about all manufacturers.

 

[furtif]

P.16

Table 4: Checking Specifications
TEST CONDITION SPECIFICATION
Leak Test Inlet 2,500-3,000 (±100) psi No leaks allowed
MP Inlet 2,500-3,000 (±100) psi
137±7 psi (standard)
123±7 psi (supreme)
MP creep Inlet 2,500-3,000 (±100) psi 5 psi max between 5 to 15 seconds
after cycling regulator (purge)


Jean-François Blard