1. Principle:
Ball Valve:The opening and closing part of the ball valve is a sphere, and the purpose of opening and closing is realized by rotating the sphere 90° around the axis of the valve stem. The ball valve is mainly used to cut off, distribute and change the flow direction of the medium on the pipeline. The ball valve designed with V-shaped opening also has a good flow adjustment function.
Gate Valve: closing member (Wedge) moves along the vertical direction of the channel axis is mainly used to cut off the medium on the pipeline, that is, fully open or fully closed. In general, gate valves cannot be used to regulate flow. It can be applied to low temperature pressure or high temperature and high pressure, and can be used according to different materials of the valve.
2. Advantages and Disadvantages
2.1 Advantages of ball valve
1) It has low flow resistance (actually 0); it can be reliably used in corrosive media and low boiling point liquids because it will not get stuck during operation (when there is no lubricant);
2) , in a large pressure and temperature range, can achieve complete sealing;
3) It can realize rapid opening and closing, and the opening and closing time of some structures is only 0.05~0.1s to ensure that it can be used in the automation system of the test bench. When the valve is opened and closed quickly, the operation has no impact;
4) . The spherical closure can be automatically positioned at the boundary position
5) . When fully open and fully closed, the sealing surface of the ball and the valve seat is isolated from the medium, so the medium passing through the valve at high speed will not cause erosion of the sealing surface;
6) . With compact structure and light weight, it can be considered as the most reasonable valve structure for low temperature medium system;
7) The valve body is symmetrical, especially the welded valve body structure, which can well withstand the stress from the pipeline;
8) The closing part can withstand the high pressure difference when closing.
9). The ball valve with fully welded valve body can be directly buried in the ground, so that the valve internals are not corroded, and the service life can reach 30 years. It is an ideal valve for oil and natural gas pipelines.
2.2 Disadvantages of ball valve
Because the most important seat sealing ring material of the ball valve is polytetrafluoroethylene, it is inert to almost all chemical substances, and has the characteristics of small friction coefficient, stable performance, not easy to age, wide temperature range and excellent sealing performance. Comprehensive features.
But the physical properties of PTFE, including a high coefficient of expansion, sensitivity to cold flow, and poor thermal conductivity, require that seat seal designs must be built around these properties. Therefore, when the sealing material becomes hard, the reliability of the sealing is damaged.
Moreover, PTFE has a low temperature resistance grade and can only be used below 180 °C. Above this temperature, the sealing material will degrade. In the case of long-term use, it is generally only used at 120 °C.
2.3 Advantages of gate valve
1) The flow resistance is small. The medium channel inside the valve body is straight, the medium flows in a straight line, and the flow resistance is small.
2) It is more labor-saving when opening and closing. Compared with the globe valve, because whether it is open or closed, the direction of movement of the gate is perpendicular to the flow direction of the medium.
3) The height is large and the opening and closing time is long. The opening and closing stroke of the gate is large, and the lifting and lowering are carried out by the screw.
4) Water hammer phenomenon is not easy to occur. The reason is the long closing time.
5) The medium can flow in any direction on both sides, which is easy to install. The gate valve channel is symmetrical on both sides.
2.4 Disadvantages of gate valve
1) It is easy to cause erosion and scratches between the sealing surfaces, and maintenance is more difficult.
3) The external dimensions are large, a certain space is required to open, and the opening and closing time is long.
4) The structure is more complicated.
Are ball valves better than gate valves?
The advantage of ball valves over gate valves is that they seal more tightly, so they are more resistant to leakage than gate valves. This is due to their 100% off feature. In addition, ball valves are easier to use than gate valves, have lower failure rates, and last longer.
The characteristics of ball valves make them ideal for shutting off control fluids.
Ball valves consistently perform well after many cycles and are reliable and capable of shutting safely even after extended periods of inactivity. For these reasons, ball valves are generally preferred over gate and globe valves.
But under the same pressure and size, the ball valve is more expensive than the gate valve.
Post time: Jun-06-2022