Slow print-spooler

I am running severel printers (IP-printing) on a NT-network. If I deliver a large number of printjobs to the spooler, following happens:
The spooler push 11 jobs to the printer, the printer finish printing the 11 jobs and display “Ready”. After several minutes (3-6) the spooler push 11 more jobs to the spooler …. .
This happens on different type of HP-printers(5, 4050 and 4500). Memory-size in the printer or print-job-size doesn’t matter.

Any idea??

Betron