On opening the gate valve, the flow path is enlarged in a highly nonlinear manner with respect to percent of opening. This means that flow rate does not change evenly with stem travel. Most of the flow change occurs near shutoff with a relatively high fluid velocity causing gate and seat wear and eventual leakage if used to regulate flow. Also, a partially open gate tends to vibrate from the fluid flow. Thus, typical gate valves are designed to be fully opened or closed. When fully open, the typical gate valve has no obstruction in the flow path, resulting in very low friction loss.