a strange memory problem

Hallo, I have a problem with my c# application, wich has about ten timer (System.threading.timer), each one makes some query on "sql server", and formats xml files. The problem is memory, process'memory doesn't grow (analyzed with many tools, like "clr profiler" or "process explorer"), but available physical memory of my "windows 2003 server" constantly decrease. All other process have a normal memory occupation , only "system cache" (from task manager) grows. Is there a way to flush system cache? Can anyone help me? Thancks in advance