Pneumatic speargun service is the difference between a gun that shoots like new for a decade and one that quietly fades until you sell it cheap. There's no rubber to swap on a pneumatic — the power lives in compressed air, sealed by a handful of o-rings and a film of oil, and those are consumables. This guide covers how the gun works, safe depressurising, the service kit, a step-by-step rebuild, sensible pressures for Mares, Salvimar and friends, and how to know when to leave a working gun alone.
How a pneumatic speargun works in 60 seconds
Inside the barrel is a sealed reservoir of compressed air and a piston. Loading pushes the shaft against the piston, driving it down the inner barrel and compressing the reservoir further; the trigger latches the piston at full stroke. Fire, and the air shoves the piston — and the shaft ahead of it — back up the barrel. The air never leaves; it's a spring you pumped once. Which means every bit of performance rests on two things: the seals that keep that air in, and the oil that keeps the seals alive. When a pneumatic "gets weak," it has almost always leaked, not worn out.
Safety first: depressurising before you open anything
A charged pneumatic stores serious energy even with no shaft in it. Before any screwdriver touches the gun, the reservoir must be fully vented. On most Mediterranean guns (Mares Sten and Cyrano, Salvimar, Seac and their relatives) that means removing the pump-valve cap at the butt and pressing the inner valve pin — slowly, in short presses, with the muzzle pointed away — until air stops hissing and the loading effort on a bare piston confirms zero pressure. Only then does disassembly begin.
The service kit: o-rings, oil and tools
The shopping list is short. An o-ring kit for your exact model — brand service kits are cheap and correct; generic rings in "close" sizes are how rebuilt guns leak on day two. The right oil: manufacturer pneumatic gun oil or a plain low-viscosity hydraulic/silicone oil per your manual — never grease, never motor oil, both of which swell or stiffen seals. Tools: the model's pin spanner or muzzle tool, circlip pliers, a wooden dowel for driving the piston, plastic picks for lifting old rings (metal picks scratch sealing surfaces, and a scratch is forever), and lint-free cloth. Add the gun's own pump, which you'll need at the end anyway.
Step-by-step teardown and rebuild
1. Vent completely, as above. 2. Strip: unscrew the muzzle, withdraw the inner barrel assembly per your model's manual, and push the piston out with the dowel; open the tail to access the pump valve. Lay everything on the cloth in the order it came off. 3. Inspect: every o-ring comes off and gets replaced regardless of looks; the piston's sealing surface and the inner barrel bore get a fingertip check for scoring; the shock absorber at the muzzle gets checked for crumbling — it's the part everyone forgets and the reason pistons crack. 4. Clean: fresh water, then fully dry; no solvents unless the manual blesses them. 5. Rebuild: oil every new ring before it goes on, seat rings with fingers and plastic picks only, and reassemble in reverse with threads lightly oiled. 6. Recharge: pump to your target pressure in steady strokes, resting the pump every twenty or so — heat is the enemy of accurate pressure. 7. Test: leave the gun charged for a day, then confirm loading effort hasn't dropped; dunk the tail and muzzle in water and watch for bubbles. Silence is a passed test.
Pressures: how much to pump and why more is not better
Manufacturers rate their guns around a working band — most Mediterranean pneumatics live happily between roughly 18 and 28 bar, with the manual's number as the anchor. Pumping past it buys less than it costs: loading effort climbs steeply (which ruins your calm at the surface and your shoulder by noon), seals and the shock absorber wear faster, and the extra shaft speed rarely survives the added difficulty of loading smoothly. A gun at moderate pressure that you can load with clean technique shoots more fish than a maxed-out gun you fight. If you need genuinely more power, that's a longer gun or a bigger piston conversation — not a harder pump.
When to service and when to leave it alone
The honest schedule: a full o-ring service every one to two seasons of regular diving, immediately after any flooding of the barrel, and whenever the gun tells you — loading effort noticeably lighter than last month, oil weeping at the tail valve, bubbles from muzzle or butt underwater, or a piston that feels gritty on the stroke. Between services: rinse after every dive, store horizontal with a few drops of oil in the barrel per the manual, and check pressure by loading feel at the start of each trip. And the counterpart rule — if the gun holds pressure and shoots true, don't open it for fun. Every disassembly is a small risk to sealing surfaces; the rebuild is medicine, not maintenance theatre. Slot the pneumatic check into the same bench afternoon as the rest of your rig — the full sequence is in the complete speargun rigging and tuning guide.
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