The opening and closing part of
gate valves is the gate plate. The movement direction of
gate valves is perpendicular to the flow direction.
Gate valves can only be fully opened and fully closed and can not be adjusted and throttled. There are two sealing surfaces in
gate valves. The wedge angle of the two sealing surfaces varies with the valve parameters, which is usually 50. When the medium temperature is not high, it is 2° 52. Wedge
gate valves can be made into a whole. The wedge
gate valve can also be made into a small amount of deformation of the gate in order to improve its process. And it also can make up for the deviation of sealing surface angle in the process of processing. This kind of gate plates are called elastic gate plates.
When the
gate valve is closed, the sealing surface can be sealed only by the medium pressure. That is, the sealing surface of the gate is pressed to the valve seat on the other side to ensure the sealing performance of the sealing surface, which is we called self sealing. Most
gate valves are forced to be sealed. They rely on external force to force the gate to the valve seat so as to ensure the sealing performance of the sealing surface. The gate plate of the
gate valve moves straightly with the valve stem, which is known as rising stem
gate valves.
Generally, there are trapezoidal threads on the lifting rod. Through the nut on the top of the valve and the guide groove on the valve body, the rotary motion is changed into linear motion, that is, the operating torque is changed into the operating thrust. When the valve is opened and the lifting height of the gate is equal to 1:1 of the valve diameter, the fluid passage is completely unblocked. However, this position cannot be monitored during the operation. When we use it, the top of the valve stem is used as a mark, that is, the position where it can not be opened is taken as its full open position. In order to consider the locking phenomenon of temperature changes, the valve is usually turned back 1/2-1 circle after fullly opening to the top position. Therefore, the full open position of the valve is determined by the position of the gate plate, that is, the travel distance. In some
gate valves, the stem nut is set on the gate, and the hand wheel is turned to drive the valve stem to rotate, and the gate is lifted. This kind of valve is called rotary rod
gate valve or non rising stem
gate valve.
The
gate valve owns the following advantages:
1. The flow resistance of
gate valves is small, and the sealing surface is subject to the heavy brush and erosion of the medium.
2. The opening and closing of
gate valves is labor-saving.
3. The medium flow direction of
gate valves is not limited, and it does not disturb flow and reduce pressure.
4. The
gate valve has the advantages of simple shape, short structure length, good manufacturing process and wide application range.
The disadvantages of
gate valves are as follows:
1. It is easy to cause erosion and abrasion between the sealing surfaces of
gate valves, so it is difficult to repair it.
2. The gate valve' dimension is large, and it requires a certain space for opening and closing. And it has a long opening and closing time.
3. The structure of
gate valves is complex. Gate valves can be classified into wedge gate valves and parallel gate valves according to the sealing surface configuration. Wedge gate valves can be divided into single gate pole types, double gate plate types and elastic gate types. Parallel gate valves can be divided into single gate plates and double gate plate types.
According to the thread position of the gate valve stem, it can be divided into two types: rising stem gate valves and non rising stem gate valves.
Installation and maintenance notes of gate valves:
1. The handwheel, handle and transmission mechanism of gate valves are not allowed to be used for lifting, and the collision is strictly prohibited.
2. The double gate valve of
gate valves should be installed vertically, that is, the valve rod is in the vertical position, and the hand wheel is at the top.
3. For gate valves with bypass valves, the bypass valves should be opened before opening to balance the pressure difference between inlet and outlet, which can reduce the opening force.
4. If the
gate valve is equipped with transmission mechanism, it should be installed according to the provisions of the product manual.
5. If the gate valve is used frequently, please lubricate it at least once a month.
