When the gate valve is opened and closed, the sealing surfaces of the valve core and the valve seat are always in contact and rub with each other, so the sealing surfaces is easy to wear, especially when the valve is close to the closed state, the pressure difference between inside and outside the valve core is high enough that leads to serious abrasion on the sealing surface. Once the valve disc of the globe valve is in the open state, the sealing surfaces are no longer in contact between the valve seat and valve disc, so its mechanical wear is less. The sealing surface of the gate valve has a certain self-sealing ability, and its valve core is tightly contacted with the sealing surface of the valve seat by medium pressure, so as to achieve high tightness. But if the medium contains some solid particles, the sealing surface is easy to be damaged.
The inclination of the wedge gate valve core is generally 3-6°. When forced to close the vale that is excessive or has a large temperature difference, the valve core is easy to be stuck. Therefore, the high temperature and high pressure wedge gate valve has taken certain measures in its structure to prevent the core from being stuck. The sealing surface of the globe valve can be sealed only when the valve is forcibly closed. Under the same caliber, working pressure and driving device, the driving torque of globe valve is 2.5-3.5 times that of gate valve, which should be paid attention to when adjusting the torque control mechanism of the electric valve.
The sealing surfaces contact each other only when the globe valve is completely closed. The smaller the relative slip between the forced closed valve core and the sealing surface, the less the abrasion on the sealing surfaces. The sealing surface wear of the globe valve is mostly caused by the debris between the valve core and the sealing surface, or the high-speed erosion of the medium caused by the loose closing state.
The gate valve has a more complex structure than the globe valve. And its height and size are relatively larger as well. From the appearance, gate valve is shorter but higher than globe valve, especially the gate valve with rising stem that needs higher height space. So in the case of limited installation space, we need to pay attention to choosing the right model.
When the gate valve is fully open, the entire flow channel is unimpeded. At this time, the pressure loss of the medium operation is minimal. Compared with the globe valve, the main advantage of the gate valve is its small resistance of fluid flow. Generally, the flow resistance coefficient of ordinary gate valve is about 0.08~0.12, while the resistance coefficient of ordinary globe valve is about 3.5~4.5. So less force is required to turn it on or off. Gate valve is usually applied in when the gate board is kept fully open or closed without frequent opening or closing gate valve, but it is not suitable for adjusting or throttling use.
In the whole process, the flow resistance and unbalance force of globe valve are large, so the required driving force or torque is correspondingly much larger. However, it is well suited for adjusting and throttling fluids. For the high-speed flow medium, the partially opened gate can cause valve vibration, and the vibration may damage the gate and valve seat sealing surface. Besides, the throttling will cause erosion on the gate by the medium.
The gate valve has a longer route than the globe valve.
When the globe valve is installed, the medium can enter into the valve core in two ways: from the bottom and the top. The advantage of the bottom entry is that the base can be free of pressure when the valve is closed, which can extend the service life of its base, and it can be replaced when the pipeline in front of the valve is under pressure. However, the disadvantage is that the driving torque of the valve is large at this time, about 1.05~1.08 times of the upper entry. And the axial force to the valve stem becomes larger, leading to the stem bending. Therefore, the bottom entry is only applicable to small-caliber globe valve (below DN50). So globe valves that are over DN200 can choose the way of top entry.
Generally, top entry is often used in the electric gate valve. The disadvantage of the top entry is just the opposite of the bottom entry. While the flow direction of the gate valve from both sides of the entry effect is the same.
Compared with gate valve, globe valve has the advantages of simple structure, good sealing performance and convenient manufacturing and maintenance. Disadvantages are the high liquid resistance and forces of opening and closing.