O-rings (especially trigger pin)

[tromic]

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.

Interesting ...
1/16 = 0.0625 and they take it to be 0.07 inch? Why not 0.06 inch?
I did not know that. Thanks!

 

[Diving Gecko]

Hehe, it was confusing for me as well. Until I kept looking at the list and saw the word "nominal" - and then to be sure I even looked it up in the dictionary:

Nominal
(of a quantity or dimension) stated or expressed but not necessarily corresponding exactly to the real value.
​

And since the numbers are from the Parker o-ring book, I think they should be trusted, but indeed a bit strange

D.

 

[popgun pete]

Hehe, it was confusing for me as well. Until I kept looking at the list and saw the word "nominal" - and then to be sure I even looked it up in the dictionary:

Nominal
(of a quantity or dimension) stated or expressed but not necessarily corresponding exactly to the real value.
​

And since the numbers are from the Parker o-ring book, I think they should be trusted, but indeed a bit strange

D.

I have an old "O" ring catalogue which lists the size of each ring in terms of both its application size and the actual physical dimensions of the ring itself in tables. The application is quoted as the "nominal" size, whereas the actual ring size is slightly smaller, say in the case of the ID of the ring compared to the shaft that it will seal on. The company that produced the catalogue and the seals is long out of business, all the sizes are listed in imperial measurements, so not much use these days, but it has sections on ring selection and interference fits, ring extrusion under pressure, shore hardness and other related matters, so I kept it.

 

[popgun pete]

Seems to me that the guy representing Seac Sub confused the part number extension S812017 with the ring number 2007 in his e-mail to you, the part numbers usually don't mean anything outside the company's own internal designation. The ring size is certainly not 2017, or 2007, but 2004. Some "O" ring assortment sets from China have ID x OD to label each group of rings in their packaging tray's individual pockets and metric sets may just be essentially re-labeled imperial sets with exactly the same rings in both sets, but with the latter described as the nearest (but not stated as such) equivalent metric size which can be very misleading when you use them to find out that they don't actually fit properly.

 

[tromic]

For O-ring ID 5/64 W 1/16 compressin would be 29%.
For O-ring ID 1.78 W 1.78 compressin would be 35%.
I took for boring (well) to be 4.2 mm and pin OD 2 mm.
Metric replacemnt would be OK!

 

[popgun pete]

The original "O" ring will be from a metric series. "O" rings are made in different size formats to various engineering standards. What is being recommended is a close substitute from a series in imperial sizes, some ring sizes are similar enough from different series to be substitutes for each other.

 

[popgun pete]

There was a discussion of Mares "O" rings on this thread http://forums.deeperblue.com/pneumatic-spearguns/91719-difficulty-determining-correct-o-rings-older-mares-pneumatics.html a couple of years ago.

One "O" ring that I have tried to substitute without any success is the Mares body tube or tank "O" ring on the "Sten/Cyrano" model guns. I once ordered a dozen ID 34 mm x SW 2 mm "O" rings from a supplier thinking that they would fit if I could squeeze the ring section down slightly as there were signs that the original "O" rings were similarly flattened after installation. As it turned out the tank tube would not slide over them, there was just too much rubber for the lip of the tank to push over the top of the "O" ring. The ID of the cylindrical alloy tank tubes is 38.0 mm and the plastic muzzle/handle boss size on the older Mares guns was of OD 37.8 mm, so they were a very tight fit in the tank tube without any "O" rings fitted; they are not such a close fit these days!

The width of the seating groove in the plastic boss for the body "O" ring is 4.5 mm and the diameter of this groove seat is 34.7 mm, so the radial gap from the bottom of the groove to the inner wall of the tank is (38.0 - 34.7)/2 = 1.65 mm. Now the original body "O" rings have a larger section width than that and removed rings which have been in place for a very long time are permanently flattened to a rectangular cross-section which I have measured at 1.66 mm in height (the old rubber must expand again slightly when removed), so that means the Mares body "O" rings are both stretched in circumference to thin their section out as well as being squashed down flat by the tank when in service. Measuring a brand new body ring taken from a Mares repair kit shows the SW to be 2.26 mm and my OD "best estimate" is 35.8 mm as those rings are not exactly round in circumference when loose, unlike the smaller circumference rings which tend to hold their circular shape, so the OD is not that easy to quantify precisely. Assuming that the OD figure of 35.8 mm for the body "O" ring is correct then the corresponding ID must be 31.28 mm. Hence that size "O" ring has to stretch circumferentially as it sits on a groove seat of 34.7 mm OD which requires an increase of 10.9% in ID. The original section width of 2.26 mm compresses down to 1.65 mm in service (to fit the available radial gap) which is a reduction of 27%, but some of that reduction is due to the circumferential stretch reducing the radial height of the rubber sitting in the groove. That is why my hoped for "replacement" metric series rings of SW 2 mm did not fit as they were not required to stretch circumferentially, being of ID 34 mm sitting on a groove seat OD of 34.7 mm and thus they did not thin out in section width at all. So replacement "O" rings need to be closer to the original ring size and not finding any I just continued to use the kit body rings scrounged from leftover sets where not all the supplied rings were used to fix a given problem.

One "O" ring size that I never got to try was "Superfect" part no. SHA/ 91 with ID 1.364" and SW 0.70" with nominal diameter of shaft or recess 1.375" and nominal diameter of cylinder or recess 1.500" (those last numbers are the application sizes, internal or external seal). The metric conversion of those numbers is ID 34.646 mm and SW 1.778 mm, with the application figures being 34.925 mm and 38.100 mm respectively. Looks tantalizingly close! "Super Seals Pty Ltd" who manufactured those "Superfect" brand "O" rings were out of business by then, the catalogue I was using was issued by them.

Why body "O" rings in particular can be damaged is that while pushing the tanks into position the sometimes sharp lip of the tank can bite into the "O" ring and cut it. I have seen this on guns where the "O" ring has been cut and then fortuitously twisted in the groove so that it still seals as the tiny cut has rotated away from the contact area by the smallest of margins. This was found on brand new guns from the factory! When the owner disassembles the gun the "O" ring twists slightly in the groove for the cut to now be back in the contact area and on reassembly the gun leaks despite the owner being careful, or the owner removed and refitted the "O" ring without noticing the cut which then was unwittingly installed in a slightly different position in the groove so that it leaks. That is why unless you examine the "O" rings for such minute cuts, indents or scratches it is best to replace all the body rings with new ones.

 

[popgun pete]

I decided to check my notes on a total seal replacement job that I performed on a Mares "Titan" many years ago, as that gun had a second groove for an "O" ring installed in the nose cone which on that "Titan" model was the same nose cone as then used in the "Sten" (the first model). Note that I was not the first person to open the gun up! The usual "O" ring groove was empty and it was only the additional groove that carried an "O" ring, a rather skinny one at that. I replaced that "O" ring with a BS 028 ring which I now realize from my old notes is the equivalent of SHA/ 91, so I did use that ring size after all. But what I had forgotten and my old notes show is that the second groove for that ring was cut to a diameter of 1.400" in comparison with the standard groove diameter of 1.375", so that is why the ring worked in that position, plus even more importantly the groove width was only 0.073" (1.85 mm) instead of the usual 0.180" (4.57 mm). I only worked in inches in those days as if you mentioned metric sizes you received strange looks from suppliers who only carried imperial sizes in stock. Metric size "O" rings were virtually unavailable and the Mares distributor was not really interested in gun repairs unless they handled them and the few dive shops back then had next to no spare parts beyond spears and speartips and the odd box containing parts from broken up pneumatic spearguns awaiting either disposal or Judgment Day for their resurrection.

The other "O" ring size I recalled was SHA/ 130 which according to my old notes was the equivalent of BS 027, but I did not use it as I have it marked as a poor match for inside the rear tail cone, not the front as I had written earlier, but have now corrected in my previous post.

The other "Titan" three main body rings were a different size to those of the "Sten", being replaced with SOS-24 (no note of BS equivalent) rings, the inner barrel seal at the muzzle was replaced with a SOS-13 (BS 115) ring. The rings on the power selector rod were replaced with SOS-2 (BS 007) and the rings on the trigger pull rod were replaced with SOS-1 (no note of BS equivalent). "BS" indicates British Standard I guess, but my catalogue did not refer to that info, I only obtained the equivalent standard sizes from the guy at the shop that sold seals and bearings, being a trade outlet for "SKF" products. Fortunately he too had a copy of the old "Superfect" catalogue and was able to work out the equivalent sizes, there being no later catalogue back then to replace it, just a few sheets of size listings from other manufacturers instead. He still had packets of some "Superfect" rings in stock, those being the "SOS" designation rings and some "SHA" sizes, but being on the other side of the counter I could not see them to check them out.

So the "Titan" was put back into action using imperial "O" ring sizes, not metric ones, as fortunately it used sizes which could be substituted, unlike the "Sten".

 

[Diving Gecko]

Hey, another o-ring question of the curious kind to the ones of you who have had your guns taken apart.
How come there is no o-ring at inlet valve (except the inside one to seal the spring-loaded ball)? At least, I can't find one and the exploded tech drawings of Assos and Hunters don't show them either.
Why doesn't the gun leak through the handle or the threads at the inlet valve?

Best,
David

 

[tromic]

There is no O-ring. You are right. It is not necessary.

 

[Diving Gecko]

There is no O-ring. You are right. It is not necessary.

Great, this means I did not drop it on the bathroom floor...
But now I am curious as to how come it is not needed? I have studied the tech drawing and I can't seem to figure it out. Where the barrel end meets the handle it is aluminum against plastic. Same with valve inlet against the handle. I am pretty sure those compartments are under pressure, so how can that seal?

 

[tromic]

Valve seals against the plastic handle. Both surfaces in contact are flat. Similar is with muzzle on front end of the gun (part 4 and 9 on schematic).

 

[Diving Gecko]

Valve seals against the plastic handle. Both surfaces in contact are flat. Similar is with muzzle on front end of the gun (part 4 and 9 on schematic).

Thanks Tomi,
And very interesting. I guess, it makes good greasing even more important in those parts.
I took my Hunter apart for the first time yesterday. I am back in Thailand where the guns are in storage and wanted to see if I could source replacement o-rings. Forgot my calipers in China though, but I'll figure it out. I'll post the o-ring measurements here once I have them confirmed. One thing I did notice was that Seac seems to use a very hard rubber compound for the o-rings. Much harder than eg. o-rings in underwater housings for cameras.

Best,
David

 

[Diving Gecko]

Tiny update.
I went to Denmark for a little while and brought my Seac to hunt a bit.
One day, I am walking down the street and coincidentally finds myself in front of a dive shop which carries a fair bit of spearo gear (spearing is taking off these days in Denmark) and the shop owner mainly has Seac gear. So, I ask for a spare set of o-rings which he, to my surprise, carries.
I leave only to find out that the famed o-ring for the trigger pin is not even in the o-ring set (I hope I was just unlucky as if I had ordered it and had it sent out to wherever to find it missing, I would feel cheated). I went back and he found two rings for me somewhere else. So, now I'll measure them all and post the measurements here as soon as I have the time.

More later in this saga...

 

[Diving Gecko]

Hi guys,
I am getting very close to compiling the exact values of the o-rings that are in Seac's replacement set. The idea is to put them into the exploded tech drawing of the gun and then upload that here so that everyone can benefit from them in the future if need be.
But I have two issues.
First one is easy. On the inner barrel there are two rings with the same inside diameter (16mm). But one is thicker than the other (2mm vs. 3mm). Does the thicker one sit at the front and the thinner one at the back? It's just so I can make sure I put them into the right place on the tech drawing.

Second one is much more tricky. I have measured all the o-rings and have found the corresponding "real world" rings. But there is one, I just can't find. It is the ring for the three main bulkhead seals.
I am almost 100% sure its section width is 2.15mm and its inner diameter is app. 31.7mm, so the ring is 31.7 x 2.15mm. (Perhaps ID is 31.5-31.6mm but section width is 2.15mm).
But I can't find an o-ring anywhere with these measurements. The closest I can get is a metric 32 x 2mm.
Have any of you heard of one with these strange measurements?

 

[popgun pete]

The only way to find out for sure is to check the "O" rings in the gun, the "O" ring at the front butts up inside the nose cone and the "O" ring at the rear seals off the barrel by sitting under the step going into the bore hole through the pressure regulator bulkhead's front face. The exterior diameter of the "O" ring when fitted is more important for this rear "O" ring as the "O" ring there is squeezed between two concentric surfaces, i.e. the inner (barrel OD) and outer (bulkhead bore step ID) seating circumferences, whereas the front "O" ring sits on the inner barrel exterior and its forward face presses against the inner wall of the nose cone's rear well without needing contact on the "O" ring's outer periphery. But which one is which is anyone's guess, you need to look at the step in the bulkhead to check the gap size that has to be sealed off.

The bulkhead or tank "O" rings are most likely special sizes; Mares guns also use a non-standard "O" ring in that location which I discussed here in post #27. At usually 3 of these larger diameter "O" rings per gun they must order a big batch of them from their supplier. Possibly there is a vested interest in selling "O" ring kits and ensuring "brand loyalty", but as small ID ("miniature") rings have numerous other applications there are a wide range of "O" ring sizes to substitute from, unlike the situation with the larger ID "O" rings.

One ring looks to be wrong on the "Hunter" diagram, I think the bulkhead plug "O" ring is number 23, not 16 as shown. "O" ring 16 is the inlet valve "O" ring which will be very small, while the transfer port should be somewhat larger which the bulkhead plug blocks off.

 

[Diving Gecko]

Hi Pete,
Thanks for your comments.
The problem, as usual, is that I don't have the gun with me here in China. So, I can't tell whether the thick or thin o-ring goes in the front. It's not a biggie at all, it was just that maybe some of you guys would know by heart and I could finish my updated diagram sooner
I hear you on the possible error on the power regulator o-ring especially because the Asso has the #23 o-ring on both ends of the power regulator. But actually while I did not have the gun with me, I did have a replacement handle which Seac sent me to deal with my leaking trigger pin issue and that handle came with the power regulator shaft installed. So, I took it out and checked it because I couldn't see why they would have changed it from the Asso. But the Hunter diagram is correct here. The front ring is smaller than the back one. Why they would make that hole smaller I can't figure out. When not plugged, I would think one would want the hole to be as big as possible to aid the movement of air.

 

[Diving Gecko]

So, here we go - these are the o-rings used in Seac Sub's replacement o-ring set art. #45600.
Seac Sub does not tell you what o-rings they use, they only give them article numbers and I wanted these specific measurements so I am not dependent on being able to get my hands on a Seac o-ring set.
Be aware that the o-ring set [at the time of writing] does not contain the trigger pin o-ring for the Hunter - that has to be ordered on the side.

I have plotted them into Seac's own schematic for the Hunter (attached here) but here it is in plain text:


#5, air tank o-ring
Measured as:
31.7 x 2.15mm (ID x W)
(I can not find a standard o-ring in this size. There is a chance that this is a proprietary Seac size. As an alternative, perhaps 32 x 2mm could work)

#6, nose/barrel o-ring
16 x 3mm (ID x W);
(One note here: I might be wrong about the placement of #6 vs. #13. The sizes are correct but maybe #6 actually sits in #13’s location and vice versa. Make sure you check where the original rings are when you take your gun apart)

#13, small block/barrel o-ring
16 x 2mm (ID x W);
(One note here: I might be wrong about the placement of #6 vs. #13. The sizes are correct but maybe #6 actually sits in #13’s location and vice versa. Make sure you check where the original rings are when you take your gun apart

#16, o-ring: power regulator shaft front, valve and possibly Asso trigger (it says 2.5 x 2 in the Asso tech drawing but I am not sure that is correct):
2.9 x 1.78mm (ID x W); AS568-006

#23, o-ring: power regulator shaft back and one-way valve in power regulator bulkhead
3.68 x 1.78mm (ID x W); AS568-007

#35, o-ring: piston
9.25 x 1.78mm (ID x W); AS568-012
(Be aware that this o-ring is not included in the o-ring set from Seac Sub [art. 45600]. You have to ask for it on the side)

#34, “oil seal” for piston

#39, o-ring: trigger pin Hunter (not Asso!)
1.78 x 1.78mm (ID x W); AS568-004

 

[tromic]

This might be useful information for Hanter owners.
You did a useful job!
Thanks Dave!

 

[Diving Gecko]

Thanks Tomi!
Actually, most of it should be valid for Asso owners also. Except the trigger pin o-ring is different for that gun (I suspect for Asso it is 2.9 x 1.78mm [ID x W]) and according to the Asso diagram, the front ring for the power regulator is also different. Other than that, they should pretty much be the same. The o-ring set that Seac sells (and which I measured) is actually on the Asso parts list and seems to contain all the o-rings needed for a full Asso rebuild.
Now, the only thing that bugs me is that I haven't been able to find the main bulkhead rings in standard sizes. But as Pete says, they might be proprietary Seac rings. Such a shame.
As an alternative for those o-rings, it could be worth trying 32 x 2mm (ID x W) as they would have the same outer diameter as the original ones.