Differences and uses of globe and gate valves
Valves and shut-off valves are used as the two most commonly used valves for shut-off purposes, the main differences between them being:
1、Different sealing surfaces
Gate valve in the opening and closing spool and seat sealing surface always contact and mutual friction, so the sealing surface is easy to wear, especially in the valve is close to the closed state, the spool before and after the pressure difference is very large, the sealing surface wear is more serious; and the valve flap once in the open condition, it is between the valve seat and the valve flap sealing surface, no longer in contact, so its sealing surface mechanical wear is smaller, but the medium if it contains solid particles, easy to damage the sealing surface. Gate valve sealing surface has a certain self-sealing ability, its spool by the media pressure tightly in contact with the sealing surface of the valve seat, to achieve a tight seal does not leak. Wedge gate valve spool slope is generally 3 ~ 6 degrees, when forced to close the excessive or temperature changes in the spool is easy to jam. Therefore, high temperature, high pressure wedge gate valve, in the structure are taken certain measures to prevent the spool jamming.
Globe valve sealing surface, must be applied to force the closure of the valve to achieve sealing, in the same caliber, working pressure and the same driving device, the driving torque of the globe valve for the gate valve 2.5 ~ 3.5 times. This should be noted when making adjustments to the torque control mechanism of the electric valve. Globe valve sealing surface, only when completely closed to contact each other, forced to close the spool and the sealing surface of the relative slip is very small, and therefore the sealing surface of the wear and tear is also very small. The wear and tear of the sealing surface of the globe valve is mostly due to debris before the spool and the sealing surface, or due to the tight closing state, caused by the high-speed scouring of the medium.
2. Different structures
Gate valve is more complex than the globe valve structure, the height of the larger size, from the shape of the gate valve than the globe valve short and high, especially the bright stem gate valve requires a higher height space, which is limited in the installation space selection to pay attention to the case.
3、Different flow resistance
Gate valve in full open the entire flow channel straight, at this time the pressure loss of the operation of the medium is minimal, compared with the shut-off valve, its main advantage is the fluid flow resistance is small, ordinary gate valve flow resistance coefficient of about 0.08 ~ 0.12, while the ordinary shut-off valve resistance coefficient of about 3.5 ~ 4.5. open and close force is small. Gate valve is usually suitable for, do not need to often open and close, and keep the gate fully open or fully closed working conditions, not suitable for regulation, throttling use.
Whereas the flow resistance of the globe valve is large throughout its stroke, the unbalanced force is large and the required driving force or torque is correspondingly much larger. But it is very suitable for use as fluid regulation, throttling. For high-speed flow of media, the gate in the partial opening condition, can cause vibration of the valve, and vibration, and may damage the gate and seat sealing surface, and throttling, will make the gate suffer from media erosion.
4. Different itineraries
Gate valves have a larger stroke than globe valves.
5. Different flow directions
When the shut-off valve is installed, the medium can enter from below the spool and from above in two ways. The advantage of entering from below the spool is that the packing is not under pressure when the valve is closed, which extends the service life of the packing and allows for the replacement of the packing when the pipe is under pressure in front of the valve. The disadvantage of entering from below the spool is that the driving torque of the valve is large, about 1.05 to 1.08 times that of entering from above, the axial force on the stem is large and the stem is easily bent. For this reason, the media from below into the way, generally only for small diameter globe valve (DN50 below), DN200 above the globe valve are selected media from above into the way. Electric globe valve is generally used to enter the media from above. The disadvantages of the medium entering from above are exactly the opposite of the way entering from below.
And the flow of the gate valve, from both sides into the effect are the same. Stop valve compared with the gate valve, the advantages are simple structure, good sealing performance, manufacturing and maintenance is convenient; disadvantage is the liquid resistance, open and close the force is large.
6、Maintenance process is different
Gate valves are not suitable for maintenance on site in the pipeline, whereas the seats and flaps of most globe valves can be replaced in-line without the need to remove the entire valve from the pipeline, which is ideal for applications where the valve and pipeline are welded together.Of course, there are more than a few differences between gate and globe valves, and we have to distinguish well between their similarities and differences in selection and use to avoid mistakes. The range of application of globe and gate valves is determined by their characteristics. In smaller channels, when a better shut-off sealing is required, more use of globe valves; in steam pipelines and large diameter water supply pipelines, due to the general requirements of fluid resistance is small, the use of gate valves.
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