DYI Scope Repair

Speaking of O-rings

The lad who did the Youtube added an o-ring to the rear end of the erector tube. I have seen pictures of some erector tubes that have a big rubber o-ring looking isolator whapped in a serpentine fashion around the entire erector tube. That, seemed to me a marvelous way to isolate a number of problems.

Pete
 
Butch Lambert said:
Gene, a few scope folks that I have visited with said it didn't stay around. It is used to purge the water in the air, but didn't hang around for ever.
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Hi Butch, Any idea how such a determination was made? And what remains? Thinking aloud - the scope should be "air tight" and nitrogen is one of the larger molecules of those that constitute "air", but it's also easy to see how difficult truly sealing a scope could be, particularly through temperature and altitude changes. The nitrogen won't just 'leave' with nothing taking its place - if the nitrogen can get out, the resulting vacuum would draw something else in. But what? "air" is nearly 80% nitrogen, most of the rest is oxygen, and then there are trace amounts of other gasses. I suppose it doesn't matter much as long as the larger-yet water molecule is kept at bay, but I don't know how you'd ever be able to determine if your nitrogen had escaped without sophisticated equipment - but there could be some kind of trick I'm unaware of.

GsT
 
GeneT said:
Hi Butch, Any idea how such a determination was made? And what remains? Thinking aloud - the scope should be "air tight" and nitrogen is one of the larger molecules of those that constitute "air", but it's also easy to see how difficult truly sealing a scope could be, particularly through temperature and altitude changes. The nitrogen won't just 'leave' with nothing taking its place - if the nitrogen can get out, the resulting vacuum would draw something else in. But what? "air" is nearly 80% nitrogen, most of the rest is oxygen, and then there are trace amounts of other gasses. I suppose it doesn't matter much as long as the larger-yet water molecule is kept at bay, but I don't know how you'd ever be able to determine if your nitrogen had escaped without sophisticated equipment - but there could be some kind of trick I'm unaware of.

GsT
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Not my expertise, just passing on what they stated.
 
ray porter said:
i have a small B sized nitrogen tank and regulator that i used to cool p dog barrels.

eventually i quit using the regulator. if you crack the valve very gently you can get small amounts out.

a regulator is certainly ideal.
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CO2 actually works better for barrel cooling.

Higher mass per molecule of gas.

Using a large zipper seal bag with a lower pressure purge of nitrogen works well.
Very large zip bags are out there.
I have a few that are 20" x 30".
Snip a lower corner and feed the gas in there.
A few rubber bands to hold the hose in the corner.

You work from the upper opening.
Close as much as you can and get to work.

I works better with some help to close off the bag.
 
Butch Lambert said:
Gene, a few scope folks that I have visited with said it didn't stay around. It is used to purge the water in the air, but didn't hang around for ever.
Click to expand...

For the what it’s worth department:Years ago a friend of mine worked for the Unertl Optical Company. At the time John Unertl junior was calling the shots. Back then they were heavily involved in government work even though John Sr. had a soft spot in his heart for sportsmen. One day during a particularly rainy deer season a fellow showed up with a fogged up 4X scope. Junior had the solution. Up stairs he went out of sight of the customer, took off the eye piece and drove out the moisture with a torch. Problem solved! Optically Unertl glass was hard to beat but left something to be desired when it came to the demands of a hunting scope.
 
Rubber seals (o-ring) are NOT 'hermetic.'
They allow some gas to leak in and out.
If the gas inside the scope is 100% nitrogen the law of partial pressures comes into play.
Since the atmosphere (14.7 PSI) is around 70% nitrogen there is a pressure difference
driving the nitrogen out of the scope.
Around 30% of atmospheric pressure or around 4.4 PSI.
Low, but still there 24 hours a day.
You can find the size of molecules and try and estimate, or just rely on the law of
partial pressures.

It is easier to slow the movement of larger molecules.
Helium is so small it can leak through a steel tank wall.
To check for hermeticity a soak in high pressure helium, followed by using
a mass spectrometer tuned to helium will tell you a leak rate. Atoms per minute.
You can count individual molecules of helium passing through the seal.

If I placed my mass spec intake against the side of a steel tank you could count
the molecules of helium passing through.
 
There is a differnece

between nitrogen purged, and nitrogen filled imo. Someone earlier mentioned a chamber with a positive purssure nitrogen feed for final assembly so as to keep dust out. If some scopes are sealed, meaning nitrogen filled and built to keep it inside, I'm not aware of which ones they are. Anyone know?
 
In 1992 myself and a group of competitors attending the NBRSA hunter national match at the Greeley Co. club went on a tour through the Burris scope factory in Greeley, this was long before Burris sold out to another company. The tour guide was John McCarty, president and part owner of Burris. We went in an area where scopes were assembled, they were assembled in a clear plastic box that had those rubber glove access holes. There was a hose supplying nitrogen into the plastic box. The box was sealed except an exhaust hole at the opposite of the nitrogen input that had a filter on it. We questioned John about this and the way he explaned it was the scopes are not "charged" as commonly thought with nitrogen but are assembled in a posatively pressurized area and that was they way to keep foreign material out.

Wayne Corley
 
glp said:
between nitrogen purged, and nitrogen filled imo. Someone earlier mentioned a chamber with a positive purssure nitrogen feed for final assembly so as to keep dust out. If some scopes are sealed, meaning nitrogen filled and built to keep it inside, I'm not aware of which ones they are. Anyone know?
Click to expand...

As long as there are gaskets made of flexible material the seal is NOT hermetic.

You need a hard metal to metal (or similar hard material) to create a hermetic seal.

Glass frit is used on military grade integrated circuit packages, or even lead seals or brazing material.

Even these seals are not helium proof though.

Hermeticity is often tested using helium.
It WILL penetrate at a slow rate, and then leak back out.
The rate of leakage back out is used to determine if there are defects in the seal.

The slightest defect causes much larger and rapid leakage.
 
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