CAST IRON GATE VALVES: Gate valves are isolation valves, and it is primarily designed to control flow, and when a straight-line flow of fluid and minimum flow restriction are needed. In service, these valves generally are either fully open or fully closed. Gate valves can be divided into two main types: Parallel and wedge-shaped. The parallel gate valves use a flat gate between two parallel seats, and a popular type is the knife gate valve designed with a sharp edge on the bottom of the gate.