I used to own a FWB 124 which seemed to leak at the breech. I never liked the seal design in this particular gun and did have some leakage which could be stifled a bit by shimming behind the seal.
That was the only springer I owned so I really do not know what is out here today.
Around a year ago I assigned myself a MSP pistol project which was to determine how fast I could shoot a 14.3 from a 9" barrel. To do this, I needed to run very high valve pressure(4500psi plus).
I post a pic of the pistol because it will show you that the breech sealing is much like a springer being that I used the barrel as a pump lever.
But this arrangement is really more prone to breech seal leakage. Because when one pumps to high pressure, much tension is applied to the pump tube and linkage which actually draws the breech away from the reciever and causes the breech seal to have less sealing capacity as higher pressure is pumped because the space between the barrel and reciever grows.
To solve the problem I used a standard o-ring groove. But I modified the o-ring. The o-ring mod was simply grinding three passages into the ring so HP air could get behind it to pressure the ring toward the join which needed sealing.
The section sketch is Exactly the way o-rings are designed to function
November 9 2010, 10:06 AM
Though the requirement for o-ring retention is often at odds with proper groove configuration, an o-ring seal is designed to be energized by the pressure differential across the sealing surface. The o-ring extrudes into a sealing shape, just as you have drawn. Rubber is NOT compressible, it needs somewhere to go....
Modification of the cheap and easy part just makes so much sense! bravo!
on one of rhe compression tubes i have for my tx i had seal issues. maybe this is a simple fix. i may give this a try. how deep do you need to make these grooves? i would think not very deep and would direct the airfflow to where you want it.
Most breach seals are so tight in their pocket air has no way to get behind the seal and rely on mechanical deformation to work; more like a gasket than a seal. As mentioned, this isn't the way o-rings were designed to work.
Unfortunately, when an o-ring is loose enough in it's pocket to work as a seal they fall out easily and trepanning a slot for the seal in a breach face is apparently too complicated in current manufacturing.
I remember something similar during the Marksman 2004 craze
November 9 2010, 11:39 AM
As I recall, the advice was to make a few small longitudinal scratches on the "post" that the o-ring sits on. The idea was the same in principle; to allow high-pressure air to get inside the o-ring. Also, to allow it back out, which was supposed to keep the pistol from blowing its o-ring off the post.
in any springer I have ever owned.
I use a piece of goose down to check, even the slightest poof of air will cause it to move.
Currently the only air rifle i have left is an FWB 124 and it has no leak at all. Unless it is leaking out in a direction that I cant check.
I did have a leak from the breech seal from my old HW EL54 Barakuda once, I replaced the seal which I have no idea how old it was, the gun was made sometime in the late 60's early 70s and I acquired it around 1985 from Beemans personal collection.
After replacing the seal never had another leak and that gun created a crap load of pressure.
Enough to deform regular pellets and make them go sssshhhiinngggg down the barrel.
The seal was actually deformed slightly, sort of looked like it was burnt.
and yes it was definitely leaking, no goose down required to feel it.
But replacing it was easy and never had another problem.
Also the HW EL54 IS a springer, it just has an ether injection tube attached to make it diesel in the extreme.
For some reason, MOST folks make the o'ring groove too narrow
November 9 2010, 2:33 PM
Which creates the problem you encountered by turning the o'ring into a "gasket" rather than a dynamic seal. By making the groove wider than the relaxed width of the o'ring, pressure can eily get behind the o'ring to force it forward and effect a seal.
Many years ago, I documented the exact opposite problem I was having with a bigbore gun I built that had a breech similar to what you describe ... when the gun fired, the breech couldn't be readily opened afterward, since the o'ring was pressed and sealed SO firmly it prevented opening.
Rather than grind those little grooves as you did, I drilled a very tiny hole through the groove floor into the barrel bore. This mod worked GREAT, as it pressurized the o'ring to effect a seal, yet depressurized when the barre was emptied.
I have used the method you discribe as well, but only with very hard stiff o'rings that are less likely to suffer damage from extruding into the notches.
BSA used a notched O'RING for awhile, which I felt was a dumb ideer, since it could really shorten the o'ring's life.
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