According to Reference.com, a sluice valve is a type of gate that is designed to control the flow of a fluid passing through it. It works by lifting a round or rectangular wedge out of the path of the fluid.
Though they can be used to regulate fluid flows in increments, sluice valves are generally not designed for that purpose and are typically either fully opened or fully closed. The main purpose of a sluice valve is either to completely allow a fluid flow or completely prevent one.
A sluice valve's ability to cut through liquids makes it a useful valve configuration in the petroleum industry.