Ball is core of Ball valve. Because of its structure of trunnion ball valve under the conditioon of high pressure, especially the closed state, the valve ball is fixed, the upper stem and lower fulcrum to decompose the part from the medium pressure, so the valve ball is not downstream migration, so the downstream seat stress in a number of relatively small.So the valve in operation to overcome the friction is small, the seat wear is small, the service life of the valve is long, especially for regular action of the valve ,this structure is more suitable.

The spool of a gate valve is wedge or parallel disc. There is no support shaft at the lower part of the valve. Thus the disc is subjected to great pressure from the medium in the high pressure service and in the closed state. Also due to its flat valve plate structure, so that all the medium pressure on the valve plate at the same time, the valve plate will be dead pressure to the downstream seat( at the same time too much pressure on the vertical surface of the valve plate, will make the valve plate whether wedge or parallel double gate, there will be certain deformation), the valve in the opening of the need to overcome the great friction, the seat wear print the valve life is short.

Seat  Structure

The valve seat has a spring inside, and the sealing design of the valve seat makes it difficult for dregs in the media to enter the valve seat. The valve seat under the action of the spring long-time contact with the valve ball, during valve operation, the valve seat has a certain role of the scraper, can be attached to the spool after long-time operation of the dregs scraped off, can ensure the valve sealing performance for long time. Especially in high temperature and high pressure applications, due to the valve seat, valve body, valve ball material in the selection of the same thermal expansion coefficient of material, and the valve seat of spring structure, when the valve closed, the huge temperature difference and temperature drop, will not affect the operation of the valve, the valve will not produce the phenomenon of dead.
Gate valve seat is very narrow, in high temperature applications, when the valve is closed, the medium does not flow, so the temperature drops, the seat will tighten, resulting in a lot of pressure on the valve plate. When the valve is opened again, a great torque is needed to overcome the compression force, which will cause great damage to the seat and affect the life of the seat. Thus affecting the service life of valve. In addition, due to the weight of gate itself when the valve is closed, it will bring a lot of impact and noise to the valve.

Stroke

Ball valve stroke is Angular, so in the installation space is small, low height. Gate valve stroke is straight stroke, so the installation space is large, high height.
Actuator
Ball valve due to Trunnion ball design, its opening and closing torque value is small, so the corresponding actuator will small. Gate valve due to the disc of the valve seat of the compression force, so the overcome this friction requires great torque, the actuator with large

Maintenance
Ball valves generally do not need maintenance, especially ball and seat, due to small wear,generally not need to replaced within 5 years.Regular maintenance is required for gate valves due to large seat wear