older Sherwood Brut piston o-rings

[gulfcoaster]

I have two old Sherwood Brut 1st stages I'm refurbishing. Both are stamped with "85" on the top of the yoke so I imagine that is the year they were manufactured. The piston part # is 3107-10 (new) which uses o-ring part #'s G007A (size 007) on the stem and G022A (size 022) on the base.

Are these o-rings NBR or EPDM? 70A or 90A? They don't feel too hard so I'm guessing they are around 70A.

Anyone know?

 

[SubseaSports]

I don't 'know', but manual calls for buna.
I have several Sherwoods old and new and they get buna with duro 70.

This thread would be best moved to the diy section for traction.

 

[gulfcoaster]

Thanks for your reply Subsea - I'm new here and feeling my way around.... How do I move a thread?

I did look again in the few maintenance guides I have found for the Brut and it definitely states that the O-rings are Buna-N. Also states that the Poppet Seat on the second stage is Buna-N which I found interesting. (I don't use the Brut second stage).

And everything I have read suggests that the softer NBR is appropriate for dynamic applications where the O-ring is providing a seal with a constantly moving part. Now I know.

 

[herman]

Typically, a 90 durometer is used where there is a large pressure differential , the piston stem for example -3k to atmosphere and a 70 durometer is used where there is a less differential like the piston head- 135 to atmosphere.

Most all of the older regs used Burna N, they will work fine unless you are planning on using high O2 mixes.

 

[gulfcoaster]

Interesting, that thought did cross my mind.... I have some 70 duro stem o-rings on the way and when they arrive I'll see if I can't "feel" a difference between them and what is on the new pistons I just purchased.

 

[herman]

They may work but are more prone to doing unwanted things. They may excessively change IP due to compressing around the stem more than a harder one would or may extrude out, leaking anywhere from slight to a big flow. Not saying they won't work but don't be surprised if you have issues with it.

 

[gulfcoaster]

Thought I'd search the board for what is being used on the piston of a similar style 1st stage, like the Scubapro MK2. Sure enough, there is reference to 90A on the neck and 70A on the base.

 

[herman]

Not the first old piston reg I have rounded up parts for.