how to remove Active users connected with FTP after x time?

Hello ,
it seems that I have a problem
I have sevral routers that send once every x hours files to my main server using FTP .
I have notice that some time the connection isn’t close - and there are too many ftp connection onlines , which cause a problem - can’t connect anymore to main server using FTP
the files arn’t big at all - the biggest files that ever been send is 0.5M .

my question - is there any way to remove the users connected after 10 min?
not to block the IP , just close the connection ?
FtpConnection.png
Thanks,

anyone?

can’t be that hard…