Some folks may recall the heads up I posted to a few forums back in January 2008, with regard to the potential danger of using brass mini Foster type fittings at pressures in the 3000 PSI range.
I have added that info to the bottom of this post, for those who had missed it back in 2008.
Just recently, there has been some banter on the forums about a "mystery metal" mini Foster that failed while a fellow was filling his gun. Some speculation arose about whether the fitting had failed due to inadvertent damage to that fitting or something similar.
A fitting that came my way today may serve to add some perspective to the failed fitting reported most recently.
At the PFT match today, one of the shooters brought me one of his guns for some TLC, and one of the items that he supplied along with the gun, was a mini Foster fitting. Almost immdeiately upon taking the fitting out of the case, I noticed that the hole through the fitting was HUGE - far larger than any mini Foster I have ever seen to date. Out came the precision hole guages and mics to measure just how thin the wall of that thing must be. While measuring the fitting, I also noticed that the hole was not concentric to the OD of the fitting - out by 0.015".
For comparison, I then took a couple of different makes of fittings that I have on hand, and measured them up. This pic tells the tale.
Fitting "A" is one of mine - made of ferrous steel. At the undercut where the locking balls engage the fitting, the OD is 0.242". The through hole (ID) is 0.079" dia. This results in a wall thickness at the undercut of 0.0815". The concentricity of the bore is within 0.005".
Fitting "B" is another one of mine, also made of ferrous steel. At the undercut, the OD of this one also measures 0.242". The through hole (ID) is 0.124" dia. So for this fitting, the wall thickness is 0.059". The concentricity of the bore is also less than 0.005".
Fitting "C" is the fitting supplied to me today - made of "mistery metal" - non-ferrous. At the undercut, the OD of this fitting measures 0.240". The through hole (ID) is 0.172", resulting in a wall thickness of 0.034". HOWEVER, the hole is 0.015" out of concentric, and when measured, the wall thickness of the thin side is only 0.026", and the wall thickness on the thick side is 0.042".
A close-up of the out of concentric bore of the mystery metal fitting.
I touched a file to the bottom of the fitting, just to remove the plating to see if the fitting was plated brass, and while it does not show well in the pic, the mystery metal is definitely NOT brass, and is silver in colour. I even took it outdoors to get a better look, to make sure that I had the best lighting possible. Seems to be similar in hardness to brass, but I won't even begin to speculate as to what the actual metal is. As well, while examining it under a 10X loupe, I could see some places that appeared to me to exhibit porousity - which would indicate a cast part. Unfortunately, all external surfaces are machined (to at least some degree), then plated, so very dificult to conclusively state that it is cast.
I have no idea as to how much use this fitting has received - it was attached to a fill probe, that was used at 200 BAR, and from what I have seen, the owner is very lucky not to have experienced having his fill whip slap him with 3000 PSI driving force, by this fitting breaking off at the undercut.
As well, this pic shows how the locking balls have begun to mark and upset the locking ridge in this soft material.
So, for your own safety, as well as those around you, check your mini Foster fittings.
If the through hole looks overly large, or if they are not known to be stainless or ferrous steel, replace them with good quality fittings obtained through a reputable source.
I have added that info to the bottom of this post, for those who had missed it back in 2008.
Just recently, there has been some banter on the forums about a "mystery metal" mini Foster that failed while a fellow was filling his gun. Some speculation arose about whether the fitting had failed due to inadvertent damage to that fitting or something similar.
A fitting that came my way today may serve to add some perspective to the failed fitting reported most recently.
At the PFT match today, one of the shooters brought me one of his guns for some TLC, and one of the items that he supplied along with the gun, was a mini Foster fitting. Almost immdeiately upon taking the fitting out of the case, I noticed that the hole through the fitting was HUGE - far larger than any mini Foster I have ever seen to date. Out came the precision hole guages and mics to measure just how thin the wall of that thing must be. While measuring the fitting, I also noticed that the hole was not concentric to the OD of the fitting - out by 0.015".
For comparison, I then took a couple of different makes of fittings that I have on hand, and measured them up. This pic tells the tale.
Fitting "A" is one of mine - made of ferrous steel. At the undercut where the locking balls engage the fitting, the OD is 0.242". The through hole (ID) is 0.079" dia. This results in a wall thickness at the undercut of 0.0815". The concentricity of the bore is within 0.005".
Fitting "B" is another one of mine, also made of ferrous steel. At the undercut, the OD of this one also measures 0.242". The through hole (ID) is 0.124" dia. So for this fitting, the wall thickness is 0.059". The concentricity of the bore is also less than 0.005".
Fitting "C" is the fitting supplied to me today - made of "mistery metal" - non-ferrous. At the undercut, the OD of this fitting measures 0.240". The through hole (ID) is 0.172", resulting in a wall thickness of 0.034". HOWEVER, the hole is 0.015" out of concentric, and when measured, the wall thickness of the thin side is only 0.026", and the wall thickness on the thick side is 0.042".
A close-up of the out of concentric bore of the mystery metal fitting.
I touched a file to the bottom of the fitting, just to remove the plating to see if the fitting was plated brass, and while it does not show well in the pic, the mystery metal is definitely NOT brass, and is silver in colour. I even took it outdoors to get a better look, to make sure that I had the best lighting possible. Seems to be similar in hardness to brass, but I won't even begin to speculate as to what the actual metal is. As well, while examining it under a 10X loupe, I could see some places that appeared to me to exhibit porousity - which would indicate a cast part. Unfortunately, all external surfaces are machined (to at least some degree), then plated, so very dificult to conclusively state that it is cast.
I have no idea as to how much use this fitting has received - it was attached to a fill probe, that was used at 200 BAR, and from what I have seen, the owner is very lucky not to have experienced having his fill whip slap him with 3000 PSI driving force, by this fitting breaking off at the undercut.
As well, this pic shows how the locking balls have begun to mark and upset the locking ridge in this soft material.
So, for your own safety, as well as those around you, check your mini Foster fittings.
If the through hole looks overly large, or if they are not known to be stainless or ferrous steel, replace them with good quality fittings obtained through a reputable source.
