Gate Valve is a sliding type of valve. In gate valves, the closing member is a metal gate. The gate slides down to close the valve. In fully open conditions, the flow area is equal to the area of the pipe and hence, there is negligible pressure drop across the valve.
Gate valve should ideally be used as on-off valve. It is not advisable to use them as throttling valves because in partly open conditions, erosion of gate might take place. In partially open conditions, due to vibrations, valve is exposed to quick wear and tear. Also, during closing and opening, there is considerable amount of friction and hence, opening and closing these vales quickly and frequently is not possible.
These valves find their use in petrochemical industry because they can work with metal-metal sealing.