How to saturate the command properly?

Hi. I have to implement a PID for the flow control. The command has to be in the range (0-100%) which controls the opening of the valve. The problem i'm confronting with is that if I have overshoot, the PID gives a negative command which is not what i want. However if I saturate the command to 0, I'll get an steady state error. So the question is... How can I have a 0% command(which means the flow is 0) so that the process response drops and does not stay still? Thanks!