Hi all. I am doing a design of controlling a fluid flow. We have some fluid which is subjected to some weight, which will serve as the external force to drive the flow. The objective is to maintain a constant flow rate. Do you guys think I shall constantly changing the opening of a valve to achieve a contsant flow? Since the driving force will produce acceleration rather than a constant velocity, we need to adjust the opening of the valve if we are aiming at a constant flow? I am wondering if there is any valve which suit this situation? The valve control should provide ways for me to change the value of the flow rate. Say, when I want a constant flow rate of 200ml/min, I may enter 200 onto a panel, then the valve my self-adjust such that a constant flow rate of 200ml/min is achieved. Is there any commercially available valve that is suitable for me?