The Bullshooter

Saturday, February 16, 2008

Filling Air Cylinders with a Hand Pump

High pressure hand pumps have been around for a number of years now, designed to fill high pressure cylinders on pre-charged air pistols and rifles. I get asked a lot about the liklihood of getting moisture in the cylinder when using these pumps. Of course it is possible, but if they are used in the way they were intended, I believe getting moisture is a pretty low possibility.

There have been a few generations of pump offered on the market over the years, starting with the Axsor. This had a matt black painted body, and was built in Sweden. Next to come along for a short time was the FX Vari-Pump, with metallic blue body and a knurled nut on the top of the handle to adjust the ease of operation. Of course if you opted for an easier pump, you had more strokes to the fill, as the nut bled off some of the pressure to make the compression stroke easier. The latest of the Swedish pumps is the new generation FX, also with a blue body. The reason I mention body color is any of the above could be tagged with a different brand... wholesalers such as Gehmann tend to market them under their own name.

The only other pump you're likely to see in use amongst ISSF shooters is the Hill Pump, made in England, with a black/gray specked body. Interestingly the Hill guys have watched all of the internet speculation about how hand pumps can potentially load damp air into cylinders and now offer a bolt-on accessory called a Dry-Pac that filters moisture out of the air at the intake. Great marketing, and possibly worthwhile for a lot of shooters just for their own peace of mind.

But even without the Dry-Pac, if you always follow these basic guidelines, you should never have any problems. I'm talking target airguns here, that use a fill adapter that mates to a 200 DIN fitting. Field Target air rifles use a quick disconnect fitting; the theory remains the same but I have no specific experience with this system.

1. Make sure the knurled nut below the pressure gauge on the pump is finger tight. This is the bleed valve for the water trap.
2. Attach your brass fill adapter to the DIN fitting on the pump. Again, finger tight is all you need. Then screw your empty or partially full cylinder to the adapter.
3. Fill the cylinder using smooth, full strokes. If you short stroke, you will take twice the time to fill it. I generally pump 50 BAR at a time to keep temperatures down (both me and the cylinder) - this keeps the chance of generating moisture to a minimum. Just take a break of a couple of minutes between each 50 BAR stage.
3A. With most cylinders you would stop at 200 BAR as this is full. These include such as FWB, Morini and Anschutz (M10 pistols and all air rifles). Be certain to open the bleed valve - this will remove any moisture from the water trap. Then you can remove the cylinder. Walther falls into the same category; although most of them are rated to 300 BAR, the pump can't go that high.
3B. I push Steyr (or Anschutz LP@ pistol) cylinders to around 210 BAR, then carefully open the valve on the water trap to bleed back to 200 before removing the cylinder from the pump. The reason for the difference is Steyr cylinders are mechanically held open by the adapter when they are screwed on. If you simply open the bleed valve after filling it, all the air will escape. The other brands rely on higher pressure to open or close the valve between cylinder and adapter.