Here is a link to the thread on our forum where these rules are being discused on page 10;
http://robowars.org/forum/viewtopic.php?t=894http://robowars.org/forum/viewtopic.php?t=894

If you can be bothered reading through it you will see that the problem with Marauder is that it is apparently over-weight and that a Sydney based robot called Stealth that won a large compition in Melbourne at the start of the year wasnt built within the rules. Its CO2 supply, regulator(if it had one) and valve came from an old soda stream system, the tubing is vacume tubing from a car as is a seperate solenoid operated purge valve. I dont know where the ram came from but the builder has drilled holes into the cylinder close to its maximum extension to exauhst the gas in the ram at full extension. He believes this makes it safe to use parts not rated for the expected pressures because the system will never reach its maximum before venting.
This is what is being refered to as an open system while since Marauder will not vent the gas in the ram imediatly on reaching full extension it is being called a closed system. At least that is how I am interpreting it.