Scuba Pro S-Wing poppet o-ring

[Couv]

Hello All,

In another thread http://www.scubaboard.com/forums/vintage-equipment-diving/311774-custom-o-rings.html some of us were discussing an alternate source for Scuba Pro S-Wing poppet o-rings. I think we have a winner here, thanks to Awap for the dimensions and Henrik for finding a vendor and getting them to us.

Here are a few pictures of the SP o-ring (01.050.363) next to the Viton o-ring. Except that the Viton is slightly lighter in color, I could not see a difference. Using a "finger durometer" test (squash the o-ring between the thumb and forefinger) I could not feel any difference. After placing one on a poppet and inserting into a barrel for a friction test I could tell no difference-same thing for placing one of each on my brass nose pick.

On the poppet the Viton o-ring it on the end
Side by side the Viton is between the 1&2 cm mark
On the pick, it is under the 2 cm mark

Couv

 

[Texfrazer]

Wow, that's awesome!

I hate that I missed the discussion and the purchase (I figured it woudl have been in here and not in vintage).

Now if we can just come up with a way to get hp seats in bulk.

 

[Couv]

Thanks to Tight Rope Walker who sent me a few samples, I was able to compare the -001-1/2 o-rings to the Scuba Pro and Viton o-rings we recently acquired. Unfortunately, the -001-1/2 are not the same size; and are in fact noticeably smaller. In the first photo, it is easy to see they are smaller than the 1mm x 2.2 mm o-rings. In the second photo, the -001-1/2 is mounted on the end of an S-Wing poppet and while it looks ok, I can tell by the feel when I insert the poppet into a balance chamber it is not the same.

I did notice a curious thing while I was doing the comparison, the stem journals where the o-rings sit are different sizes. The journal with the o-ring that first goes into the balance chamber is slightly larger than the other one. I checked it with my dial calipers and found that the larger one is approx 0.091 inches and the smaller one at approx 0.077... I checked two poppets and got the same results. A little experimenting revealed that taking the o-ring off the larger journal, place the balance chamber on the stem and draw a vacuum through the poppet, it will not hold vacuum. It will however hold vacuum with just one o-ring on the larger journal. Awap suggested a while back that one o-ring could be serving as a wiper as the other holds the pressure, but I would think even if that were the case, if the primary failed, the other should be able to serve as a backup.

If any of you have any ideas why this poppet is designed this way, I would appreciate hearing them.

Oh....by the way, placing the -001-1/2 on the smaller journal resulted in a very noticeable vacuum leak. Placing it on the larger journal and it held vacuum (as applied by mouth) but I have not tested it hooked up to IP pressure.

(yes, I know I have to get a life)

Thanks,

Couv

 

[halocline]

I haven't taken the ones that Henrik sent me out of the bag to compare them to originals. I assume the ones you're talking about here are different, right?

 

[Couv]

The ones Henrik sent us are a perfect match, see post 1 in this thread, the -001 1/2 are a bit smaller, see post 3.

c

 

[Couv]

....I did notice a curious thing while I was doing the comparison, the stem journals where the o-rings sit are different sizes. The journal with the o-ring that first goes into the balance chamber is slightly larger than the other one. I checked it with my dial calipers and found that the larger one is approx 0.091 inches and the smaller one at approx 0.077...

I would like to get your input in this thread. As mentioned above, I measured a couple of S-Wing poppets and found that the two o-rings are the same size, however each sits on different size journals. Also, counter to my understanding and experience with most o-rings, they sit very loosely on the seat. If memory serves me correctly, most of the o-rings I have come across seem to be stretched a bit more for a tighter fit which would seem to help prevent extrusion. The o-rings on this poppet seem very loose. I know there is very little pressure differential on them, but what would be the purpose of this?

Thank you,

Couv

 

[redacted]

SP has done the same thing with the groove diameters of the 2 LP o-rings on the Mk20/25 composite piston. This was what made me originally conclude that the second o-ring was designed as a means of protecting the inner o-ring from dirt and damage rather than as a redundant seal. If both were the same diameter, I suspect you could get some pumping effect that may move contaminants into the protected chamber should the o-rings fail.

 

[Puffer Fish]

Ok, I am officially impressed with the work you guys have done getting the correct o-rings... good going.

Before getting to the issue of the second o-ring... would like to remind everyone that Viton is not one material... there are a bunch of different types and blends... and that durometer is just a measure of hardness, not wear, or rebound or friction (set down off the soup box Puffer.. set down).

An o-ring makes a terrible wiper...kind of the wrong shape, but any moving cylinder part that is not completely sealed is going to need a wiper of some sort. Ideally, one would use, well a wiper seal.. but that adds a lot of complexity to the parts list, so the next option is to use an o-ring.

As extruding is not an issue...and it is a moving part...giving one a slightly bigger slot would allow the o-ring to move a bit and slighty distort. I have seen this used on a few pieces of non scuba equipment.

Only thing I would worry about is using an o-ring with very different properties in that location...not sure how that would actually effect the performance.. it is sort of important that the o-ring slight roll with each change in direction.

Never actually had the chance to test how effect this concept is..as the travel direction versus the pressure is usually opposite.....I would guess the design is one based on experience and practical problem solving.

 

[Couv]

Thanks Awap and Puffer,

OK that pretty much solves the mystery of why the outer o-ring has play on the journal/groove-to serve as a wiper- but why would the inner sealing o-ring have (although somewhat less) play? Usually dynamic o-ring are slightly stretched over the groove they sit in and compressed slightly into the cylinder to give a good seal. When I have time, I'll check out some of the old blue poppets and balance chambers to see if they were the same.

C

 

[Puffer Fish]

Thanks Awap and Puffer,

OK that pretty much solves the mystery of why the outer o-ring has play on the journal/groove-to serve as a wiper- but why would the inner sealing o-ring have (although somewhat less) play? Usually dynamic o-ring are slightly stretched over the groove they sit in and compressed slightly into the cylinder to give a good seal. When I have time, I'll check out some of the old blue poppets and balance chambers to see if they were the same.

C

I believe that is a factor of how much extrusion forces the o-ring is under and how much compression the o-ring will experience.

Never looked at your part in question, but usually see that where the o-ring, when installed has room to be flattened.

This is also a plastic part, with low forces on it, so it may just be done because the application allows it. As the extrusion forces go up, tighter and tighter tolerences are required, but tighter tolerences cost money...