Most likely air leak locations in Pneumatic Guns

[popgun pete]

The air leak points for a pneumatic speargun of the Mares "Sten" and its clones from other companies are not that many. The places where seals have movement are the most common, which are the piston rings, the power control selector shaft ring and the trigger transmission pin ring. Rarely unless you disturbed it or got some foreign substance lodged in it is the inlet valve "O" ring that serves as the inlet valve seat. Another "O" ring that can leak due to damage during repair work or a faulty installation is the nose cone to inner barrel "O" ring that can be damaged when sliding it over the nose end screw threads on the inner barrel. Use grease when replacing these seals, but not too much, just enough to make them slippery to aid sliding them into position.

[popgun pete]

As air leaks can also be caused by cracked pistons and shock absorbers, the latter being damaged can crack the piston or the piston can smash both itself and the shock absorber anvil face in a hit harder than the gun was originally designed for. Early pneumatic spearguns had metal pistons and shock absorber anvils, but cheaper plastic was substituted in the seventies. This was OK provided gun pressures are kept low, but partly relied on pushing water out of the inner barrel to take the edge off the terminal impact on the shock absorber anvil. However vacuum barrel conversions of the same guns, often achieved by screwing on new vacuum seal enclosing muzzles, have pushed the plastic piston to its limits. What is required is a shock absorbing piston to add to the damping provided by the muzzle shock absorber. Such a shock absorbing piston would look like this.

Note the metal tip would have to do the spear pushing as we don't want shaft acceleration to collapse the new piston shock absorber. So while the usual taper on the spear tail held the spear in the gun on the piston nose's tapered entrance, as soon as the piston moves the metal spine extension would be driving the shaft,