Stainless steel gate valve

First, the characteristics of the gate valve

The gate valve refers to a valve in which the closing member (gate) moves in the vertical direction of the center line of the passage. The gate valve is mainly used for cutting in the pipeline.

The gate valve is a widely used valve. It is generally used for cutting devices with a diameter of DN ≥ 50 mm. Sometimes the cutting device with a small diameter also uses a gate valve. The gate valve has the following advantages:

1. The fluid resistance is small.

2. The external force required for opening and closing is small.

3. The flow direction of the medium is not limited.

4. When fully open, the sealing surface is less affected by the working medium than the shut-off valve.

5, the body shape is relatively simple, casting process is better.

Gate valves also have shortcomings:

1. The external dimensions and opening height are large. The space required for installation is large.

2. During the opening and closing process, there is relative friction between the sealing surfaces, which is likely to cause scratches.

3. Gate valves generally have two sealing faces, which add some difficulties to processing, grinding and maintenance.

Second, the type of gate valve

1, according to the structure of the gate can be divided

(1) Parallel gate valve: The sealing surface is parallel to the vertical center line, that is, the gate valves whose two sealing surfaces are parallel to each other.

In the parallel gate valve, the structure with thrust wedges is often common, and there are double-sided thrust wedges in the middle of the two gates. This gate valve is suitable for low-pressure medium and small diameter (DN40-300mm) gate valves. There is also a spring between the two shutters, and the spring can generate a pre-tightening force, which is beneficial to the sealing of the shutter.

(2) Wedge gate valve: the sealing surface is at an angle to the vertical center line, that is, the gate valve with two sealing surfaces forming a wedge shape.

The angle of inclination of the sealing surface is generally 2?52?, 3?30?, 5?, 8?, 10?, etc., the angle depends mainly on the temperature of the medium. Generally, the higher the working temperature, the larger the angle should be taken to reduce the possibility of wedges when the temperature changes.

In the wedge gate valve, there are also single gate, double gate and elastic gate. The single-gate wedge gate valve has a simple structure, but has high precision on the angle of the sealing surface, is difficult to process and repair, and is highly likely to be wedged when the temperature changes. Double gate wedge gate valves are used more often in water and vapor media lines. The utility model has the advantages that the precision of the angle of the sealing surface is low, the temperature change is not easy to cause the wedge phenomenon, and when the sealing surface is worn, the gasket can be compensated. However, there are many structural parts, which are easy to bond in a viscous medium and affect the sealing. More importantly, the upper and lower baffles are prone to rusting for a long time, and the ram is easy to fall off. The elastic gate wedge gate valve has the advantages of simple structure, simple use, and the ability to produce a slight amount of elastic deformation to compensate for the deviation caused by the sealing surface angle process and improve the processability. use.

2, according to the structure of the valve stem can be divided into

(1) Open gate valve: The stem nut is on the valve cover or bracket. When the shutter is opened and closed, the valve stem is lifted and lowered by the rotary stem nut. This structure is advantageous for the lubrication of the valve stem, and the degree of opening and closing is obvious, so it is widely used.

(2) Dark rod gate valve: The stem nut is in the valve body and is in direct contact with the medium. When opening and closing the shutter, use a rotary valve stem to achieve. The advantage of this structure is that the height of the gate valve remains the same, so the installation space is small, and it is suitable for large-diameter or gate valves with limited installation space. This structure is equipped with an opening and closing indicator to indicate the degree of opening and closing. The disadvantage of this type of construction is that the stem thread is not only lubricated, but also directly etched by the medium and is easily damaged.

Third, the structure of the gate valve

If the diameter of the passage in a valve body is different (often the diameter of the valve seat is smaller than the diameter of the flange joint), it is called the diameter contraction.

The shrinkage of the diameter can reduce the size of the parts, reduce the force required for opening and closing, and expand the application range of the parts. But after the path is contracted. The fluid resistance loss increases.

In certain operating conditions in certain sectors (such as oil pipelines in the oil sector), valves with reduced diameter are not permitted. This aspect is to reduce the resistance loss of the pipeline, and on the other hand to avoid obstacles to the mechanical cleaning pipeline after the diameter shrinkage.