Learn › Track 02 · Equipment & physics
Pumps, tanks & compressors
A PCP pistol is only as good as the air you put in it. Its cylinder is small, often about 19 cm long and 3 cm across, yet you fill it to 200 bar. Before choosing how to fill it, get a feel for how much air that really is.
Think first: A pistol cylinder holds about 100 cc. Filled to 200 bar, roughly how many litres of air is that at normal pressure?
Three ways to get high-pressure air
You have three choices: pump it yourself, decant it from a big tank, or compress it with a machine. Most shooters end up using two of them.
- Hand pump — Three-stage pumps are rated to about 300 bar · No refills to arrange, works anywhere · Slow, tiring, and the pump heats up
- Tank (scuba or carbon) — Scuba tanks are 200, 232 or 300 bar · 300-bar carbon-fibre tanks give many top-ups · Needs refilling at a dive shop or by a compressor
- Compressor — Portable 300-bar units fill a tank or the cylinder directly · No pumping, no trips to the dive shop · At ISSF competitions, compressed air is provided on site
Hand pumps: slow and dry
A match hand pump squeezes the air in three stages to reach high pressure. Squeezing air heats it, so a long session makes the pump hot. Pump with slow strokes, keep sessions short, and let the pump cool between them.
Think first: Your pump has an intake filter, and you live somewhere humid. What can still get into your pistol’s cylinder?
- Nothing — the filter stops it
- Water vapour — a filter stops dirt, not humidity
- Pump oil, but only if you pump too fast
Tanks: decanting
A big tank works like a bank of air. You connect it to the pistol cylinder, open the valve, and air flows until the cylinder reaches the pressure you want. The tank loses a little pressure with every top-up. Once the tank drops below 200 bar it can no longer fill your cylinder all the way.
With a 3 L tank at 300 bar and a 100 cc cylinder topped up from 100 to 200 bar, the simple sum gives about 30 top-ups. Real air doesn’t behave quite like the sum, so expect a few less. Now try a 12 L scuba tank at 200 bar. It holds a lot of air, but it gives you no full fills at all.
Carbon-fibre tanks have their own life rules. A typical 300-bar carbon tank must be retested every five years and retired at fifteen. The markings on your tank decide, not a general rule.
Fittings: DIN and yoke
The connection between tank and fill hose has to hold 300 bar. There are two main types. A yoke clamps the fitting against an O-ring that sits in the face of the tank valve. A DIN fitting screws into the valve and traps its O-ring inside. DIN valves come in 232-bar and 300-bar versions, and the 300-bar socket is two threads deeper.
Think first: Your new tank has a 300-bar DIN valve. Your fill adapter is a 232-bar DIN fitting. What happens when you screw it in?
- It seals fine, but you must stop filling at 232 bar
- It won’t seal: the fitting is too short to reach the seat
- It seals better, because the extra threads hold it tighter
Hot fills
Compressing air into the cylinder warms it, and warm air reads high on the gauge.
Think first: You fill to 200 bar and the cylinder is warm, about 40 °C. Once it cools to a 20 °C room, what will the gauge read?
Which air source suits you?
Think first: You shoot three times a week at home and top up your 100 cc cylinder from 100 to 200 bar about twice a week. Your club has no compressor, and the nearest dive shop is an hour away. Which setup makes most sense?
- A 12 L, 200-bar scuba tank, because it holds the most air
- A small 300-bar carbon tank, refilled at the dive shop every few months, plus a hand pump as a backup
- A hand pump only, used twice a week
Whatever you choose, check the pressure rating of every part between the air source and your pistol. Read the next lesson before you fill anything: Cylinders: lifespan & safety.
- A 100 cc cylinder at 200 bar holds about 20 litres of air.
- Hand pumps: slow strokes, short sessions, a desiccant against moisture. Filters stop dirt, not water.
- Tanks decant until they fall below your fill pressure. A 3 L, 300-bar tank gives about 30 top-ups. A 200-bar tank gives no full fills.
- DIN traps the O-ring. A 300-bar DIN valve is two threads deeper, so a 232-bar fitting can’t seal in it.
- Warm fills read high: 200 bar at 40 °C settles to about 187 bar. Top up after it cools.