Help with First Stage Identification and "O" Ring Sizes

[NotSure]

I bought this first stage a while back to use in my shop because it was cheap and had a DIN connector which were my only requirements. It was dirty and corroded looking when I got it but it cleaned up really nice. I decided to go ahead a disassemble it to see what was inside and it looks good inside also. The piston "O" ring appears to be a -120 and the stem a -007. It has four 3/8" LP ports and one 7/16" HP port. At first I didn't even care what I had, but after I cleaned it up so nice I got curious. My guess is that it is a Aqualung of some type, but would like to know for sure. I would appreciate it if some one could identify this regulator for me and confirm it has the correct "O" rings inside.
Notsure

 

[Couv]

I have no idea of the make of that first stage.

However, you should be able to determine the correct size by measuring the groove outside diameter (O.D.)of the part you want to install an o-ring on. Note that o-rings should be slightly stretched (1-5% with 2% being recommended) Therefore, after you measure the groove, multiply by 0.98 to find the inside diameter (I.D.) of the o-ring you need. Almost all scuba o-rings have a cross section (c.s.) of 1/16" (1.78mm) so any o-ring with a "0" after the dash will have a c.s. of 1/16 (1.78mm) and that makes finding the correct seal pretty simple.​

​

For instance, if you measure the stem groove and get a dimension: 0.116 multiply by 0.98 to get the I.D. 0.11368 you need and find the closest match (or next smaller) with a dash number beginning with -0 at a site like ​

www.oringsusa.com/html/size_chart.html

and you come up with a -006. ​

 

[NotSure]

Thanks for the information couv. The stem "O" ring groove measures 0.159", so if I multiply by 0.98 I get 0.156" which is 5/32" and matches a -007 as I suspected. The piston measures 0.993" X0.98=0.973" which the closest smaller size would be 15/16" or 0.938". The piston groove is 0.125" wide and the inside of the piston chamber measures 1.169". The current "O" ring is 0.093" wide which makes the CS 3/32". If I subtract the piston groove diameter from the piston chamber diameter I get 0.176"/2=0.088" clearance. This would seem to be about right for a 3/32" "O" ring to fit tight. The installed outside diameter of the "O" ring would be 0.993+(3/32)X2=1.181" which is about 1% larger than the piston chamber. Seem to me this calls for a -119 instead of the -120 I originally suspected.
Any thoughts,
Notsure

 

[Couv]

You may have lost me on one of the o-rings, but it seems to me
The piston stem o-ring should be a -007
The piston head o-ring should be a -021
And the other o-ring should be a -119
Is that an o-ring that seals between the cap and the body?

I just had a peek at the MK 2 schematic, and the piston stem o-ring is a -008 while the piston head o-ring is a -022
As Brother Zung pointed out in another thread, you can probably go up or down one size with no detrimental effects especially in low pressure applications.

 

[NotSure]

You may have lost me on one of the o-rings, but it seems to me

I can barely understand what I wrote, I should have drawn a sketch. I was accually only describing two "O" rings, everything after the first sentence refers to the large piston "O" ring which I now believe is -119.