Using octo as a primary

[jiveturkey]

I just read another thread that talked about y and h valves and I got to thinking. If I was to switch to a config where I had 2 first stanges and 2 second stages instead of an octopus, could I use my scubapro R380 octo as the second primary (???). As far as I know the only difference is that it's yellow.

 

[rmediver2002]

I just read another thread that talked about y and h valves and I got to thinking. If I was to switch to a config where I had 2 first stanges and 2 second stages instead of an octopus, could I use my scubapro R380 octo as the second primary (???). As far as I know the only difference is that it's yellow.

Your right, the components are the same. You would just need to either adjust it or have someone adjust it.

The spring is at a slightly higher tension than when adjusting a primary.

Jeff Lane

 

[DA Aquamaster]

I don't think there is any reason to make your own adjustments in this situation. If you have are taking it in for service soon, or if you buy another SP first stage from the shop, the shop can set it up for you as a primary at that time for no extra charge. Alternatively, if you have had it serviced recently, they should readjust it for you for free.

A new Mk 2 Plus first stage only is around $100 at an SP dealer, a MK 16 will run about $150 and a MK 25 will run around $190 to $200 after the 10% discount is applied.

On the R380 and R190, the pre-sets are different when setting up the reg as an octo. When setting up as a primary, the nyloc nut is tightened until one full thread is exposed. The orifice is then adjusted for a cracking effort in the 1.2 to 1.4 range.

When setting one up as an octo, the nyloc nut is thightened so that 2 full threads are exposed which loads the spring more heavily. Then when the orifice is adjusted you get a cracking effort in the 1.8 to 1.9 range.

In either case it is very important to then re-adjust the nyloc nut to take any additional slack out of the lever that may have resulted from adjusting the orifice. Failing to do so can severely limit the amount of air the reg can deliver.

If you buy a new first stage the second stage will need to be adjusted for peak performance when matched with another first stage as the adjustments are IP dependent and the IP can vary between 125 and 145 psi. The shop will do this for you for free, so there is not really any reason to do it yourself. Again, adjusting your own reg in this situation is not something I would recommend.

The yellow color can be a good thing as you automatically know what reg you are breathing from. This is critical if you ever move to independent doubles or for some reason use manifolded doubles with the isolator valve closed.

 

[SterlingDiver]

On the R380 and R190, the pre-sets are different when setting up the reg as an octo. When setting up as a primary, the nyloc nut is tightened until one full thread is exposed. The orifice is then adjusted for a cracking effort in the 1.2 to 1.4 range.

Interesting details. I have SP R390's for both secondary & octo on a MK16. I am curious why they both wouldn't be set-up the same? I am sure there is a reason. My Octo is definitely harder to breathe on.

SterlingDiver

 

[jiveturkey]

Interesting details. I have SP R390's for both secondary & octo on a MK16. I am curious why they both wouldn't be set-up the same? I am sure there is a reason. My Octo is definitely harder to breathe on.

SterlingDiver

It's tuned down to make freeflow less likely.

Thanks for the explanations guys. Although my head is spinning after yours DA Aquamaster. lol

 

[DA Aquamaster]

I personally think 1.8 is a little extreme even for an octo and prefer to set them around 1.4 with the primary at 1.2 for R380/R390's. The purge covers are stiff enough that unintentional free flows are not really an issue as long as the viva knob is set close to minimum. If your shop is well equipped and has a clue what they are doing, they can set it up for you any way you like.

A good shop or tech will ask you how you like your regs set up and then ensure they breathe that when they tune them after the annual service. They should also provided you with a test sheet with the pre-and post test numbers. If you are charged for service, you really should get good service.

 

[jiveturkey]

So what are your options for routing your secondary reg with this configuration? Do you route it the same way as an octo? Down the right hand side?

 

[jiveturkey]

By the way, that's a sweet reg set up you have in your profile picture. :biggrinba