Swap space on DEC Alpha 4100

I have multiple DEC Alpha 4100 servers on a TCP/IP network, running Tru64 Unix 4D. My problem is that when one server goes down for a backup, the swap memory does not seem to clear down, because after every backup less swap memory is avaiable. It escalates until the server falls over due to lack of swap memory. The servers are equiped with 1.5Gb RAM and 3Gb swap space. Any ideas to solve this problem? Thanks.