This is not information specific to your gun, but it should be enough
information for you to figure it all out yourself, which is better
anyway.


In paintguns, the cup seal is a high pressure fitting that seals the
valve of the gun closed.  When the gun fires, the cup seal and the
cup seat separate, and lots of CO2 rushes through (usually down a
tube or past a post) and pushes the ball out the barrel.

If your gun leaks (usually out the barrel) when you screw the tank
on, you've got a problem with the cup seal.  It may have some dirt
or metal chips imbedded in it, or it could be damaged.  Also, if your
velocity is low and you can't adjust it up, this can be caused by a
worn cup seal.  Sometimes firing the gun a few times will stop a
leaky cup seal from leaking, for a while anyway. (this is sometimes
called "re-seating the cup seal")

You'll have to take apart your gun's valve to get at the cup seal.
Most guns will not be very hard to take apart.  Pumps have much simpler
valves than semis.  Be careful that you keep trck of the order of the
parts in the valve. (especially for a semi)  Lay them down on an old
towel or something, with the end that faces you sitting face-up.  Line
them across the towel in order, so you can just go down the line putting
them back in later.

When you take things apart, you may as well take it all apart. (the
valve I mean)  Once you get all the parts taken out, get a q-tip and
clean out the inside of the valve.  Use force.  There's all kinds of
grime and rust particles and old oil in the bottom of the 50lb bulk
tanks they fill your CA talk with, and it all ends up in your valve.
Cleaing the inside of the valve will keep your cup seal working
well.  This is mroe important with semis that have multiple 0-rings
in the valve.  Not keeping the valve body clean can make the o-rings
leak, which can jam your gun.  Clean any o-rings.  Also clean off
the cap that you removed to get into the valve.

Most valves have the cup seat on the valve body's cap.  They come in
all shapes and sizes, but whatever it is, the cup seal presses against
it to close the valve.  If it's dirty or damaged, your gun will leak.
The cup seal may be black rubber, or a milky or clear plastic/nylon.
It's probably very hard, and will be fitted into a "cup", which is
usually attached to a post or tube.  This post will extend out the
valve body and is what the hammer hits to open the valve and fire the
air charge.  Clean off the cup seal carefully and make sure there are
no brass chips imbedded into it.

Before assembling, give everything a light oiling with some 3-in-1 or
other lightweight oil.  Unlike most other parts of the gun, the valve
cannot be harmed by excess oil, so don't be afraid to overdo it a
little.  (though you will be ejecting oil out into the barrel if
you REALLY soak it)  Be sure that the cup is tightly screwed onto
the post - they have a nasty habit of comming unscrewed, and this can
cause serious damage when you fire it.

If your cup seal appears worn, or has a groove in it or something
that might not allow it to seal well, it CAN be repaired if you are
careful.  Get a small heat gun, butain torch, or candle. (a lighter
will not do)  With the cup seal still in the cup, hold it with a
needle-nose pliers and VERY slowly heat it.  Slow heating is the key.
View the cup seal at an angle, so when you see it get near the heat
it should immediately appear to steam up.  Hold at this distance for
about 90 seconds.  During this time you should see the surface of the
seal slowly liquefy, and any scratches, pits, or dents will fade away.
Don't heat for more than about 90 seconds at a time, giving it a few
minutes to cool down between attempts.  Only one session is usually
necessary.  Don't touch the seal between sessions - it must be allowed
to cool for at least 10 minutes before puting it back in the gun.
If you heat it too fast, (too close to the heat source) you will burn
the seal, and this is usually fatal to the seal.  After "rebuilding"
the seal in this way, you will probbly have to re-seat it.  Gas up
the gun (don't be alarmed if it leaks a little) and fire it a few
times.  It should sowly stop leaking, and then be fine.  The cup seat
is pressing into the cup seal and is forming a new meeting surface.
Once this is done, it will be good-as-new.  This process works best
on the clear, white, or opaque seals, but is very hard to do well
on black rubber seals. (they burn very easily)