Selection Principles of Gate Valves
Advantages of gate valves
1. The medium’s flow direction will not be changed because gate valves belong to the through type valve which also makes gate valves feature in small flow resistance.
2. The sealing performance of gate valves is better than that of globe valves, and the opening and closing of the gate valves need less effort than globe valves’.
3. Gate valves have a wide range of applications. In addition to steam, oil and other media, gate valves can also be applied to the media with granular solids or viscosity, used as air release valves or valves for the vacuum systems.
4. Gate valves have double flow directions, so they will not be limited by the flow directions of the media, which make them suitable for pipelines with the media which may change their flow directions and make them easily installed in pipelines.
Disadvantages of gate valves
1. Gate valves usually have big sizes, and the opening and closing time of them is usually long. When the gate valve is being opened, the gate has to be lifted to the upper part of the valve cavity, and when the gate valve is being closed, the gate has to fully fall into the bottom of the valve seat, which make the stroke as well as the opening and closing time long.
2. The sealing surfaces of gate valves may be damaged in the opening and closing processes due to the friction between the gate’s sealing surface and the valve seat’s sealing surface, which may trigger the bad sealing performance, the shortened service life and difficult maintenance of the gate valve.
The performance comparison among different gate valves
Single wedge type gate valves
1. The structure of the single wedge type gate valve is simple than that of the flexible gate valve.
2. Under the high temperature conditions, the single wedge type gate valve has worse sealing performance than the flexible gate valve and the double disc gate valve.
3. The single wedge type gate valve is suitable for the high temperature easy coking media.
Flexible wedge gate valves
1. The flexible wedge gate valve is the special type single wedge type gate valve. Compared with the wedge type gate valve, the flexible wedge gate valve has excellent sealing performance under the high temperature conditions and will not get stuck by the gate when it is heated.
2. The flexible wedge gate valve is applicable for steam, high temperature oil, gas media, and the parts of pipelines which need to be opened and closed frequently.
3. The flexible wedge gate valve can not be used for the easy coking media.
Double disc gate valves
1. The double disc gate valve has better sealing performance than the wedge type gate valve, and the good sealing performance can be kept even when the inclination angle of the sealing surface does not accurately suitabel for the valve seat.
2. When the sealing surface of the gate wear and tear, it is only needed to change the metal gasket, and there is no need to overlay or grind the sealing surface.
3. The double disc gate valve is suitable for the steam, high temperature oil, gas media, and the parts of pipelines which need to be opened and closed frequently.
4. The double disc gate valve can not be used for the easy coking media.
Parallel slide gate valves
1. The parallel slide gate valve has worse sealing performance compared with other gate valves.
2. The parallel slide gate valve is suitable for transporting the low temperature and low pressure media.
3. The processing as well as the maintenance of the parallel slide gate valve valve seat’s and gate’s sealing surface are much simpler than other gate valves’.
Installation precautions of gate valves
1. The valve cavity and the sealing surfaces should be check carefully whether there is some dirt or sand on them.
2. All the parts of the gate valves should be connected tightly and evenly.
3. The packing of the gate valve should be pressed tightly so that not only the sealing performance of the packing will be guaranteed, but also the flexibility of the gate will be ensured.
4. The model, the size for connection and the flow direction of the media are supposed to be examined carefully before the gate valve is installed.
5. The gate valve must be maintained regularly and can not be collided with and squeezed, or the sealing performance of the gate valve will be influenced.
Source: China Gate Valves Manufacturer – Yaang Pipe Industry (www.ugsteelmill.com)