The following principles apply:
It is significant for the design that conditions, which are as constant as possible, are to be strived for in the measuring tube. The application determines the point of installation of the regulating valve. Most of the processes are close to atmospheric at the outlet side. In this case, the flow control valve is placed on the inlet.
There are processes, in which the pressure is not stable downstream from the flow meter. In this case, the regulating valve needs to be placed at the outlet.
Warning: In this configuration, it is very important for the adjusted inlet pressure to be stable and to coincide with the designed pressure in the measuring tube. This arrangement is considerably more stable, because the depressurizing takes place downstream from the regulating valve (see also stable flow in response to changing conditions).
In the case of liquids, the valve should also be placed on the outlet, so that possible gas bubbles encased in the liquid have a smaller volume under pressure and can accumulate to a lesser extent at the float.