Huben Dry firing a Huben semi auto...

[Airgun-hobbyist]

Because some PCP's shouldn't be dry fired too often I got to thinking about the Huben semi auto and tried to wrap my head around how it works. Would dry firing a Huben, with their new type of valve operating system potentially damage the valve or something else? Anyone familiar with the Huben's system please explain it and if there's any potential to damage it from uncontrolled blasts of air.

Searching didn't produce the definitive answer as to whether releasing a blast of air with no ammo to push (to "control" the release of air) is bad or otherwise not good. Because Huben's air valve and operating system is not the same as the "standard" PCP system where a compressed spring pushes a weighted hammer into a valve stem to release air, it may be possible to do damage and we'd all benefit from knowledge of the system going forward. Thanks.

 

[AlanMcD]

There are no issues with dry firing a Huben. It does not hurt it at all. Interestingly, it releases much less air when there is no pellet in the mag slot than when there is.

The Huben actually has two valves - one that opens to fire the gun, and the other is the closing valve, and this one is how the power is adjusted by the power wheel. It closes off the air flow when the pressure drops in the barrel.

Here is an illustration of how it operates:

 

[Airgun-hobbyist]

Thanks for posting the animation video AlanMcD. That was a very detailed rendering of the inner workings. I had watched this video of the parts breakdown several times and had the basic concept.

 

[AlanMcD]

Thanks. I found that video to be very helpful. What might not be clear from it - because they don't let the gun sit long before firing it again in the animation - is that the normal resting position on the vertical closing valve is in the down position. It is designed to not fully seal at the top, and during the shot, when the valve is in the up position cutting off the air flow, a little bit leaks by it. When closed it cuts off the air flow pressure thus allowing the spring to reset the firing valve (and this allows the trigger to reset too). Once the firing valve is closed, the pressure above the closing valve rises to regulated pressure, and then the closing valve resets to the down position allowing full air flow (based on its setting) on the next shot.

The other thing that happens when the closing valve initially closes is that the pressure drops in the piston that drives the magazine advancement so it retracts. As the pressure rises in that piston (which is all connected in the plenum space after the closing valve) after the firing valve closes, the rod drives the magazine forward to the next round - and then the last part of the trigger reset takes place making the gun ready to fire again. It is 100% mechanical, no air is vented to drive anything (all vented air is used on the projectile), and it is very fast in how it cycles - the mag can be dumped in under 5 seconds if you are good (enabled because the trigger only mechanically resets the second stage, meaning the movement to fire again is only a millimeter or so, depending on how the trigger is set).

It's just a brilliant set up. Interestingly, I also have a Sidewinder and the closing valve on it must work differently somehow, despite the obvious similarity of the guns - the Huben gives a tiny blip of air when dry fired, but the Sidewinder gives a huge dump of air when dry fired. The sidewinder can easily be emptied by dry firing (although it is better to do it off the regulated pressure gauge) while the Huben would take forever (they recommend removing the firing valve reset spring, replacing the rear cover, and firing the gun to completely drain the reservoir - off course if you only want to empty the regulated space that can be done with the factory regulator alone - just reduce pressure to zero).