Basic Introduction of Gate Valve
Gate valve refers to the closed parts (wedge) moves along the
central line of the vertical direction. Gate valves are mainly used for cutting
in the pipeline. Gate valve is used widely, especially most of DN≥50mm cutting
devices, sometimes small diameter cutting devices also adopt gate valves.
I. Advantages of Gate Valves
1. Fluid resistance is very low.
2. It is small that the external
force for opening and closing.
3. The flow direction is unrestricted.
4. When fully opened, the erosion of gate valves’
sealing surface is much less than globe valves’.
5. The shape is relatively simple, and the casting procedure is better.
II. Disadvantages
of Gate Valves
1. Both the dimension and the opening height are large. The space required for
installation is also large.
2. In the process of opening and closing, there is relative friction between
the sealing surfaces, which is liable to cause scuffing.
3. Gate valve generally has two sealing surface,
processing, grinding and maintenance to increase some difficulties.
III. Category
of Gate Valves
1. Wedge Structure
1） Parallel gate valve: the sealing surface is
parallel to the vertical central line, that is, the two sealing surfaces are
parallel to each other. Thrust
wedge structures are most common in parallel gate valves, that is, double-sided
thrust voussoir is located between the two gates. Also, the spring could be located between the
two gates, the spring can produce the tightening force which is useful to the
sealing of gates. This kind of gate valves is usually used in low pressure and
small size（DN40—300mm）
condition.
2） Wedge
gate valve: the sealing surface is in a certain angle from the vertical
centreline, i.e., the two sealing surfaces are wedge shaped gate valves. The inclined angle of the sealing
surface generally includes 2°52´, 3°30´, 5°, 8°, 10°etc., and the size
of the angle mainly depends on the temperature of the medium. In general, the
temperature is higher, the angle should be taken greater to reduce the
possibility of wedging when the temperature is changed.
In the wedge gate valve, there are
single wedge gate valve, double wedge gate valve and flexible wedge gate valve.
Single wedge gate valve is characterised by simple structure and reliable use,
but the precision of sealing surface angle is higher, and processing and
maintenance are more difficult, it is very easily wedged when the temperature changed. Double
wedge gate valves are usually used in water and steam medium lines. Its
advantages are the precision of sealing surface angle is low, and it is not
easy to wedge when the temperature
changed. Also, if the sealing
surface weared, the gaskets can be added to apply the compensation. But this
kind of structure has too many assemblings, it is easy to bond in the viscous
medium and influence the sealing performance. It is much more important that
the upper and lower baffles are easy to rust when used for a long time, and the
wedge is easy to fall off. Flexible wedge gate valve, it has the advantages of
simple structure and reliable operation same as the single wedge gate valve,
and also it can produce deviation micro elastic deformation of the cover
sealing surface angle in the process, which improves the process and now widely
adopted.
2. Stem
Structure
1）O S&Y Gate Valve：Stem
nuts are located on the valve bonnet or yoke. When opening and closing the
wedge, rotates the stem nut to achieve the lifting of the stem. This structure
is beneficial to the lubrication of the valve stem, and the degree of opening
is obvious, so it is widely used.
2）Inside Screw Gate Valve： The
stem nut is in the valve body and also directly contacts with the medium. When
opening and closing the wedge, rotates the stem nut to achieve. The advantages
of this structure include that the height of the gate valve is not changed, so
the installation space is small, and also suitable for large size or limited
installation space. The structure shall be equipped with an opening and closing
indicator to indicate the degree of opening and closing. The disadvantage of
this structure is that stem threads are not only lubricated, but also subject
to erosion by media and are easily damaged. The disadvantage of this structure
is that stem screws are not easily lubricated and damaged, also subject to
erosion by media.
IV. Path
Shrinkage of Gate Valve
The internal diameter of a gate valve
is different (usually the diameter of valve seat is smaller than the flange
joint), it is called path contraction. The path contraction can reduce the size
of parts and the force of opening and closing, and also enlarge the
application scope of parts. But the fluid resistance loss is increased
when the path is contraction. In some departments under certain operating
conditions (such as the petroleum pipeline), the valves with the path
contraction are not allowed. This is to reduce the resistance loss of the
pipeline, on the other hand, in order to avoid the obstacles for the mechanical
cleaning pipeline after the path is contracted.
DBV VALVE GROUP
is committed to continuous innovation, strict control of production, and
provide the best industrial valves, such as gate valve, ball valve, butterfly
valve, globe valve, check valve, etc. for
you.
