The tanks require, in my experience, just as much attention as the operating system of the FN303. To start with there seems to be a distinct lack of solid information on the requirements for having them hydrostatically tested. Looking around various paintball forums I see a variety of people talking about something called the “2×2″ rule which exempts them as they are less than 2” diameter and 2′ in overall length. Then another place I see that Catalina has a notice out that cylinders made by Cliff Impact Division are exempt. Based on that, and the convenient fact that my local dive shop doesn’t seem to care, the test date doesn’t seem to be an issue.
What will be an issue, in my experience, is that these used FN303 tanks seem to have as many o-ring issues as the launchers. Where the o-rings inside the launchers were significantly degraded and rotten the problems with the o-rings in the tanks seem to be caused by the red sand. It appears that there was no effort to keep sand out of the fill port and sand was subsequently injected into the tanks when they were recharged. An easy way to help prevent this sort of problem is to install some fill port covers. I found some cheap ones on Amazon and they snap on nice and tight.
Rebuilding the tanks is relatively straightforward with a few basic tools. To start place the flats of the valve assembly in padded vise jaws and then turned the tank off, a task which requires varying level of effort. On a couple of tanks it was possible to grip the tank tightly and turn if off by hand. For the majority however it took a bit more force and a strap wrench was required. Don’t waste your time with nylon strap wrenches from auto parts stores as they will slip. The one to get is the $5 rubber strap wrench set from Harbor Freight. Initially I had my doubts about the strength however they worked perfectly. On the most stubborn tank I had to put both strap wrenches on at the same time to have “handles” on either side of the tank.
Once the tank is removed the next step is to remove the fill port. The easiest way to do this is to simply clamp it in the vise and turn the valve assembly by hand. One of my tanks had some corrosion on the “out” port which prevented the hose from effectively sealing however that seems to be an exceptional circumstance. For most tanks there is no reason to remove the “out” port, pressure gauge or burst disk. Next step is to remove the on/off valve cam from the body which is simply a matter of removing the small set screw from the handle and then pushing it out the bottom. The final disassembly step is to remove the valve from the assembly. This requires snap ring pliers after which the valve and spring assembly should simply fall out.
The o-rings required to rebuild the valve cam assembly are two of the common XX used throughout the launcher. The fill port valve and on/off valve require two of the small o-rings used in the “on/off” trigger mechanism in the launcher and finally the neck of the bottle requires a unique sized o-ring. Removal of the smaller o-rings is a bit challenging and I chose to simply cut them off with an X-Acto knife taking care not to nick the channels the o-rings rest in. Installation of the two small o-rings is simple as they can be pressed on. The larger o-rings on the valve cam typically require a bit of coaxing with a small flat blade screwdriver.
On a couple of my tanks I found that the snap ring and lock washer were a bit rusty and I replaced them with matching parts from my local Ace Hardware. The majority of the tanks simply require a good cleaning to remove any sand or other crap that would prevent the o-rings from giving a good seal. Assembly is simply the reverse of how it came apart. One thing to note is that if you install the on/off plunger assembly prior to installing the on/off cam then you will likely need to use a small Allen wrench to depress the tip of the valve or it will cause the cam to hang op when you are pressing it in.
If you should find that your tank is damaged, corroded or you otherwise feel uncomfortable re-using it there are newly manufactured Catalina / Cliff Div tanks available from MCUS for $50. At 17 cubic inches they are slightly smaller volume than the original tank, which I estimate at 20ci, however I have have been unable to find a exact replacement for it. I have also been unable to find any close replacement for the valve assembly or the mounting hardware.