A gate valve, also known as a sluice valve, is a valve which opens by lifting a 

round or rectangular gate/wedge out of the path of the fluid. The distinct feature 

of a gate valve is the sealing surfaces between the gate and seats are planar, 

so gate valves are often used when a straight-line flow of fluid and minimum 

restriction is desired. The gate faces can be parallel, but are most commonly 

wedge-shaped. Gate valves are primarily used to permit or prevent the flow of 

liquids, but typical gate valves shouldn't be used for regulating flow, unless they 

are specifically designed for that purpose. Because of their ability to cut through 

liquids, gate valves are often used in the petroleum industry. For extremely thick 

fluids, a specialty valve often known as a knife gate valve is used to cut through 

the liquid. 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. Also, a partially open gate tends to 

vibrate from the fluid flow. 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. 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 frictionloss.