O-rings (especially trigger pin)

[Diving Gecko]

Hi guys,
So, I have trouble with the sealing of the trigger pin on my Seac Hunter (face-lifted version of an Asso).
The gun is not with me now, so all this is from memory. No pics unfortunately.
Twice have I had a leak around the trigger pin and bushing. After the first leak, the local dealer changed the o-ring. It was good for a while, but then started leaking again. I was away from any type of service center, so needed to service it myself. I noticed that the o-ring was oversized - as in that the inner diameter was a fair bit bigger than the pin (by at least 1mm). The way it would seal was by the bushing compressing it. It seemed weird as I know from servicing push buttons on underwater camera housings that they do not depend on heavy compression at all.
With the gun trigger pin there was a sweet spot where it would seal depending on how far in the bushing was screwed, but this sweet spot was very small - perhaps within a quarter or less of a turn of the bushing. If the bushing was too lose, the pin would leak. If it was too tight, it would be sealed but the pin would jam.
So, my question is whether this is the normal way for the pin to be sealed or whether the o-ring is too big?

The following may not even add to understanding this and it might actually cloud the issue but since have actually asked Seac I wanted to share that as well. But the thing is, their answer doesn't really make sense. What they said is that the O-ring needed was a "2-007" and that that o-ring measures 1.78x1.78mm (ID and width of 0-ring). That would sound plausible as the pin in the Hunter is supposedly 2mm. But when I looked it up, the 2-007 ring mentioned by Seac is actually 3.68x1.78mm, so Seac is confusing me as either the model designation is wrong or the measurement is. Certainly they don't go together and I don't know which one is the correct one. (I asked, but they did not get back to me with an answer).
Any ideas?

Also, does anyone have a list of the o-ring sizes needed for all seals in an Asso gun? It would be great to put a full spare set together.

Best,
David

 

[popgun pete]

1.78 x 1.78 mm does not sound right as a ring size. 3.68 x 1.78 mm is more likely and should be the ring OD x ID. The "Asso" ring is 2.5 x 2 for a larger pin size than used in the "Hunter". When the guy in the shop changed the ring he may have used the wrong one, but crushed it to compress the ring and obtain a seal. I think you should buy a kit as you can waste a lot of time finding out if rings fit. Plus you can measure them up if you want to make a note of the sizes as the kit rings will be in pristine condition. In that application the "O" ring should be an interference fit on the shaft, not loose, even before you do the retaining bush up. Send an e-mail to ask Seac Sub to confirm the size you were quoted the first time, someone may have made a mistake and also ask what those dimensions represent as "O" rings can be described in different ways, not everyone uses the same format.

 

[popgun pete]

To give you a guide I measured up a new "Cyrano Apnea" trigger "O" ring. It is difficult to measure without squeezing the ring, the calipers just have to touch lightly, so it is easier said than done, however the OD looks to be 4.6 mm. The section width is 1.5 mm, I repeated the measurement a few times and that seems to be the figure. So the ID of that ring is 4.6 - (2 x 1.5) = 1.6 mm. Now I could be slightly out, but this ring has to seal on a 1.5 mm diameter trigger transmission pin and the clearance will therefore be 0.1 mm or 0.05 mm on either side of the pin and maybe not even that allowing for measurement error as you can be squeezing the rubber down on the section width or catching the fine mold line on the ring circumference.

I pulled the trigger pin out of my "Cyrano 550", it was already depressurized, and pushed it through the new "O" ring after wetting it and it is a snug fit on the pin, so the ring section width must be larger than I measured it as. Even though unused the sides of the "O" ring look slightly flat, so maybe that gives a low reading. I did not measure the ID directly as my metal calipers have sharp internal jaws and I did not want to scratch the bore of the new ring. I have plastic calipers, but they are inaccurate and not much good for precise measurements.

 

[Diving Gecko]

I had a feeling you'd weigh in on this Pete.
Thanks a bunch and it makes a lot of sense. Push buttons on camera housing work the same as you describe. They are a snug/perfect fit on the pin and then there is slight compression on the outer side of the ring when inserted into the bore.

In regards to the sizing confusion on my pin, I did ask for clarification from Seac, but they never got back. I may be demanding too much, but I have to admit, I was even a tad disappointed that they did not ask for the name of the dealer who serviced the gun (They import directly from the factory, they told me). I think Seac should contact them and tell them to step up their game. But when I get to the gun again, I'll photograph the ring and send it to them. But again, I am probably expecting too much.

Sourcing o-rings is at least cheap for me as I live in Shanghai and I can get them easily.
I agree with you, that 3.68 x 1.78mm could sound about right, but when I look up what Seac called the standard "2-007" ring, it is actually stated as being 3.68 as the ID. So, in the regard 1.78 x 1.78mm makes more sense, as that would actually be 5.34 x 1.78mm (OD and ID) and would make sense with a snug fit on a 2mm pin. BTW, that o-ring is called 2-004 in the screenshot, I am attaching.
I think I will source these rings and triple check with Seac and also ask them where to get a full replacement set of seals for a Hunter.

All best and thanks again,
David

 

[tromic]

What is the OD of the boring for O-ring? It might be about 4.5 mm or so... For Cyrano (1.5 mm pin) it is about 4 mm.

 

[Diving Gecko]

Problem is, I don't know... Don't have the gun with me here in China.

But it could likely be the same as the Asso?

 

[tromic]

Does not Asso have 3 mm pin? Your is 2 mm?

 

[Diving Gecko]

Yes, true, but I was thinking that the bushing OD size might still have stayed the same and they might just have made the pin smaller, but perhaps not.

 

[tromic]

I had a feeling you'd weigh in on this Pete.
Thanks a bunch and it makes a lot of sense. Push buttons on camera housing work the same as you describe. They are a snug/perfect fit on the pin and then there is slight compression on the outer side of the ring when inserted into the bore.

In regards to the sizing confusion on my pin, I did ask for clarification from Seac, but they never got back. I may be demanding too much, but I have to admit, I was even a tad disappointed that they did not ask for the name of the dealer who serviced the gun (They import directly from the factory, they told me). I think Seac should contact them and tell them to step up their game. But when I get to the gun again, I'll photograph the ring and send it to them. But again, I am probably expecting too much.

Sourcing o-rings is at least cheap for me as I live in Shanghai and I can get them easily.
I agree with you, that 3.68 x 1.78mm could sound about right, but when I look up what Seac called the standard "2-007" ring, it is actually stated as being 3.68 as the ID. So, in the regard 1.78 x 1.78mm makes more sense, as that would actually be 5.34 x 1.78mm (OD and ID) and would make sense with a snug fit on a 2mm pin. BTW, that o-ring is called 2-004 in the screenshot, I am attaching.
I think I will source these rings and triple check with Seac and also ask them where to get a full replacement set of seals for a Hunter.

All best and thanks again,
David

I would say your O-ring is 2-004, not 2-007. That is: ID 5/64 (1.98 mm) x W 1/16 (0.158 mm). Conversion in table is wrong! In that case boring OD for 2 mm pin might be 4.2 mm.

 

[zmajmr]

[ame="https://www.youtube.com/watch?v=u3J00MkDO90"]O - rings for trigger mechanism - YouTube[/ame]

 

[popgun pete]

Yes, true, but I was thinking that the bushing OD size might still have stayed the same and they might just have made the pin smaller, but perhaps not.

Does the "Hunter" manual have a parts list? Interestingly the only "O" ring size quoted in the "Asso" manual is that for the trigger "O" ring, the rest of the "O" rings are referenced by their application in the gun. The "Asso" manual has been available on-line for many years. The boring or well in the "Asso" has to be large enough to accommodate that "O" ring, which is quoted at (ID) 2.5 x (SW) 2, so the ring OD must be 6.5 mm. SW is section width and in some catalogues it is RW or rubber width, same thing.

Your problem partly stems from never having seen the original "O" ring, I remember you saying that the shop had two "Hunter" guns in stock and both were leaking oil in that trigger area. The shop owner changed the "O" ring the first time and that meant you never had the chance to examine the "O" ring he took out. In any discussions with Seac Sub you should mention that fact as your new gun was not exactly stock, even though you purchased it as such from their dealer. The original fitment "O" ring may have been nicked, the small pin has a rounded end and a flat end and if the factory assembly person sticks the flat end through the "O" ring then the sharp edge can tear the "O" ring just enough to create a slow leak. The pins have an inner end and an outer end, but not everyone notices that fact with these small diameter metal pins.

 

[Diving Gecko]

Hi Pete,
The problem also stems from my bad memory - as I did indeed try to fix the first leaking o-ring, but, for the life of me, I can't remember whether that one was a snug fit or not. I know that the second one was not.
I am attaching the parts list for the Hunter here, look for part #39.
Interesting that the Asso pin ring size is specified.
In Marko's video above, he mentions numbers as well, but I don't know if they are measured and I don't know if they are for the Cressi or Asso (maybe they are the same). But his are (ID) 2.9 x (SW) 1.78 which amounts to (OD) 6.46, so either way it is close. I'll attach a screenshot of that video also.
When I service my UW cam housing, as said, the rings are a snug fit and the outer bore puts a bit of compression on the ring. I once read that this is exactly how o-ring usage should be. It should be designed with a bit of compression. I think it was about 15-30%.

 

[tromic]

Both Asso and Cressi have 3 mm pin. Your is 2 mm. So your O-ring ID should be <= 2 mm. 1.98 would be perfect, as I already wrote.

 

[Diving Gecko]

Hi Tomi,
I am fully aware of that
But Pete mentioned that Seac published the size for the Asso ring, so I wanted to back that up with what I saw in Marko's video.
My problem is the confusing email from Seac where they state a "model number" which does not match with the measurements of that same o-ring is they give it.

Here is that email:
"Hi David,
please see the enclosed file that can help you to understand and find the spare parts; the o-ring that you need is the 2007(standard measure in the world 1,78 mm internal diameter X 1,78 mm thickness)

I hope that these information are useful for you to solve the trouble."

But the standard 2007 (mostly called 2-007) that he mentions is not 1.78 x 1.78. It is instead (ID) 3.68mm x (W) 1.78mm.
(Tomi, when you looked at the form last time and said the conversions didn't make sense, it's because you did the math from the nominal column (eg. 5/32 inches and not the actually size specified in the column next to it)

I will reach out to Seac one last time on the matter and let you guys know if they feel like setting this straight. As it is now, their parts list is wrong as it states a 2007 ring also.

Best,
David

 

[tromic]

I am sure your O-ring could not be 5/32 but 5/64. So 2-004, not 2-007. Or, you could use 1.78 x 1.78. That would be OK.

 

[Diving Gecko]

Yes, I suspect 2-004 should be the right one. Also, because Seac mentions measurements of (ID x W) of 1.78 x 1.78mm which are the specs of a 2-004 (when you go for the actually and not nominal specs in inches) and also sounds perfect for a 2mm pin.
But then they need to change their parts list also. But I am going to source those rings for sure to start with

I'll update in a few months' time when I am back to my gun in Thailand. Or if Seac comes back with a final answer, I'll update as well.

What would be very cool is to start compiling all the o-ring sizes for as many different guns as we can. I'll look for a complete Hunter replacement o-ring set. Maybe I can have it sent to Denmark and pick it up in the summer when I will be visiting.

Thanks again Pete and Tomi!

 

[tromic]

I would say your O-ring is 2-004, not 2-007. That is: ID 5/64 (1.98 mm) x W 1/16 (0.158 mm). Conversion in table is wrong! In that case boring OD for 2 mm pin might be 4.2 mm.

Math conversion (inch to mm) in table is wrong, but that is a possible metric replacement: ID 1.78 mm x W 1.78 mm!

 

[Diving Gecko]

Hi Tomi,
Both yes and no, I think. But again, you are the engineer
But here goes:
The fractions mentioned (like 1/16) are "nominal" which basically means that they are not the accurate sizes, but the are close to and what people use in everyday language. If you convert these nominal sizes, you will indeed find they are wrong.
The real, accurate sizes are mentioned in inches as well and if you convert those to metric, you'll find that they are spot on.
So, eg. what they call 1/16, they also say in real, actual size is 0.070 inch which will convert nicely to 1.78mm.


D.

 

[Diving Gecko]

Oops, but that still don't explain why in reg. to the 2-004 ring they say it is 5/64 and 1/16 but then say that is .070in and .070in...

And this, I think is even from Parker's O-ring Handbook.

D.

 

[Diving Gecko]

Oops, but that still don't explain why in reg. to the 2-004 ring they say it is 5/64 and 1/16 but then say that is .070in and .070in...

And this, I think is even from Parker's O-ring Handbook.

D.

Oh, actually the "nominal" designation may explain it again. Nominally, it is 5/64 x 1/16. In reality it is 0.070 x 0.070... That's what their list says anyways - and it even says that the nominal sizes are only for reference.