As a certified pumper nut, here are a few things I do to resolve some sealing issues that can arise, as well as a couple tricks to reduce pumping effort in your 13xx, 22xx pumper.

Detecting and repairing leaks

Due to the relatively small volume of air used per shot, the 13xx and 22xx pumpers can suffer drastic power loss from relatively minor leaks. Large leaks can be detected by firing your gun while cupping one hand over the breach. Smaller leaks can be detected by using a couple drops of water on each side of the breach near the transfer port or one drop placed on the bolt after closing. Leaks will be shown as a water spray.

Listening carefully to the muzzle (gun must be unloaded!), while very slowly placing one pump into your gun, will help detect a faulty valve stem. The hissing of a valve stem leak will usually be amplified by the barrel.

Check valve repair

Once in a while you get a gun with chronic power problems, you tear it down, replace o-rings, inspect stems and check valves, clean out debris and reassemble only to have the gun make good power for a less than ten rounds, followed by substantial power loss. Often the culprit is check valve tolerance. The check valve either has a very slight deformity on it's face or is just a hair too big.



Chuck the check valve in your lathe or drill press and with a small folded piece of 120 grit sandpaper remove material from the smallest diameter section (first step behind the face). Use the folded edge of the sandpaper and slight pressure. Test fit the check valve into the valve body, with dry parts the check valve should fall into and out of the body if inverted. If it sticks rechuck and repeat, follow up with some 320 grit sandpaper to smooth the surfaces. You can also use the 320 grit to slightly reface the check valve. With slight pressure press the 320 against the face and slowly move back and forth for a couple seconds. If your check valve has major deformities, replace it.

Reducing pumping effort

Pumping effort can be reduced with a small revision to the valve.



Install a lighter valve spring, I use a 9/32" x 1 3/8" x 0.028" century or dynaline spring, in valves with the newer short check valve. This will reduce the check valve opening pressure, which also results in a greater volume of air delivered per stroke as well as reduced pumping effort. It's also possible for the hammer spring to now overpower the valve spring, in this case the gun must be partially cocked to charge, as well as being stored with 2-3 pumps. If you don't want to cock the gun to charge it, you can balance the springs by slowing cutting back the hammer spring. Cut no more than 1/3 to 1/2 coil per test fitting and ideally you should reclose the spring each time.

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