TargetTalk

The college team I help coach has a Hammerli 480 fill adapter that has been dropped a few times over the years. This is one of the nice ones that rotates so you can fill the tank while it's still on the pistol. It apparently always landed DIN side down, and the groove for the O-ring was so beat up the O-ring wouldn't stay in anymore.

I made a tool and pushed the metal back out, but it now needs a new O-ring. I can scrounge one from a spare solid fill adapter, but I figured it must be whatever is typically used for scuba DIN fittings. Well, I bought one of those, and it's way too fat to fit in the groove. The standard scuba O-ring is 0.103" cross section, but the Hammerli groove is only ~ 0.068" wide. That works out to 1.73 mm, so I suspect a 2mm O-ring might be about right.

Does anyone know what size O-ring Hammerli uses on their fill adapters? There is no mention of it in the manuals. I suspect it's the same for any of their PCP pistol adapters that fit a DIN scuba valve. This the big O-ring that lives in a groove on the end face of the adapter.

Thanks!

This may help:

http://lakeshoreseal.com/MetricChart.htm

I usually buy o-rings through McMaster-Carr. You'll probably have to get a bag of 50 or 100, but it will only be a few bucks.

Roger

That was my plan, but the metric O-rings are closer to $8 a bag, so I'd like to narrow down the size first. As a guess, a 2.0mm x 14mm (ID) O-ring looks like a strong candidate, but a 2.4mm x 14.3 is another possibility. The next time I'm at the range, I can try to check one with a caliper, but measuring O-rings is a bit like clamping Jello. It's hard to get a definitive result.

Yeah, I know measuring o-rings with a calipers is a bit iffy. Especially if they've been in use for a while and have some permanent deformation.

I have some experience specifying o-rings for lab apparatus. I don't know what the adapter seat looks like, but maybe I can help you make a good guess if no one else has the exact answer.

Ideally the o-ring should be preloaded in the same direction as the anticipated pressure. In other words, if the pressure is on the I.D. of the ring pressing outwards, then the ring should fit in the seat so that the O.D. is against the wall of the seat and there is a gap between the I.D. and the seat. The gap gives it room to deform as it compresses in assembly. Also, the seat should be deeper than 1/2 the diameter of the ring, i.e., less than half the ring is projecting above the seat. So I would suspect that the 1.50 mm is the correct width.

All of which goes out the window if someone who actually knows what he's talking about is willing to chime in.

Roger

I found I had some 2.4 x 14.3 mm O-rings, and although the cross-section is close, the major diameter is too large.

I used to do oceanographic instrumentation, so O-rings & I are old friends (enemies?). In this case, the O-ring is working more like a conventional gasket, as it gets compressed between the fitting and the scuba valve. The outside of the groove it sits in is beat to heck from all the dropping & repair work, so I'm relying on the bottom of the groove to provide the seal. Even bashed up, it worked OK until we could no longer gt an O-ring to stay in place.

Looking at the ISO/DIN spec. chart the inner diameter is 14.00mm and the cross section is 1.80mm.

That is close to what I measure on my DIN adapter.

Murray

Thanks! 1.8mm x 14mm is a standard size. Unfortunately, McMaster Carr doesn't seem to carry it, so I'll have to track them down elsewhere. Apparently Shore 90 hardness is also recommended for these pressure levels, which is also a bit hard to find.

MSC Industrial has 14mID x2mCS O-rings in both Buna-N for $13.34, and Viton for $21.00. These prices are for a bag of 100pcs. I believe Buna-N, a type of Neoprene, is what you're looking for. The difference in cross section of .2mm is less than .008" hardly significant in an O-ring. Below is a link to the page with the items.

http://www1.mscdirect.com/eCommerce/Sea ... allpartial

Paul

Check with Pilkington!

They had an odd one for an FWB C-20.

Pz

Here's another supplier, carries 14 x 1.8mm

Paul

http://www.applerubber.com/products/o-rings.cfm

Thanks! I've bought from Apple in the distant past, but they seem to have expanded their metric offerings substantially. It even looks like they have a number of 2.2mm cross-section O-rings, which are non-standard, but are used extensively in the Tau-7 CO2 pistols.

I'll make up a shopping list, and ask for a quote.

Aha! The plot thickens...

It turns out the 1.8mm x 14mm is within the tolerances of a standard US O-ring size:

14mm = 0.551"

1.8 mm = 0.071"

AS 586-015 O-rings are 0.551 ± .007 by 0.070 ± .003

These can be obtained easily at most decent hardware stores for ~ $0.50 each, or in bulk from McMaster for $2.62 for 100 in Shore 90 hardness.