older Sherwood Brut piston o-rings

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gulfcoaster

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Location
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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?
 
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.
 
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.
 
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.
 
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.
 
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.
 
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.
 

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