Types of gate valves and working principles

The opening and closing parts of the gate valve are the gate plate, the direction of movement of the gate plate is perpendicular to the fluid direction, and the gate valve can only be fully opened and closed, and can not be adjusted and throttled. The ram has two sealing faces, and the most commonly used mode gate valve has two sealing surfaces forming a wedge, and the wedge angle varies with the valve parameters, usually 50, and 2°52' when the medium temperature is not high. The gate plate of the wedge gate valve can be made into a whole, which is called a rigid gate; It can also be made into a ram that can produce a slight amount of deformation to improve its manufacturability and make up for the deviation of the sealing surface angle in the processing process, which is called an elastic ram

 

The types of gate valves can be divided into wedge gate valve and parallel gate valve according to the sealing surface configuration, and the wedge gate valve can be divided into: single gate type, double gate type and elastic gate type; Parallel ram type gate valves can be divided into single ram type and double ram type. According to the thread position of the stem, it can be divided into two types: open rod gate valve and dark rod gate valve. When the gate valve is closed, the sealing surface can only rely on the medium pressure to seal, that is, the sealing surface of the ram plate is pressed to the valve seat on the other side by relying on the medium pressure to ensure the sealing of the sealing surface, which is self-sealing. Most gate valves are forcibly sealed, that is, when the valve is closed, the ram should be forcibly pressed against the valve seat by external force to ensure the tightness of the sealing surface.

 

If the gate plate of the gate valve moves in a straight line with the valve stem, it is called the lifting rod gate valve (also called the open rod gate valve). Usually there is a trapezoidal thread on the lifting rod, which changes the rotary motion into a linear motion through the nut at the top of the valve and the guide groove on the valve body, that is, the operating torque into the operating thrust.

 

When the valve is opened, when the ram lift height is equal to 1:1 times the valve diameter, the flow of the fluid is completely unobstructed, but this position cannot be monitored during operation. In actual use, it is marked by the vertex of the stem, that is, the position that cannot be opened, as its fully open position. In order to account for the lock-up phenomenon due to temperature changes, it is usually rewound 1/2-1 turn back to the apex position as the position of the fully open valve. Therefore, the fully open position of the valve is determined by the position of the ram (i.e. stroke). Some gate valves, the stem nut is located on the gate, and the handwheel rotates to drive the valve stem to rotate, and the gate plate is lifted, and this valve is called the rotary rod gate valve or the dark rod gate valve.

 

Gate valves have the following advantages

 

1. The fluid resistance is small, and the sealing surface is less brushed and eroded by the medium.

 

2. It is more labor-saving to open and close.

 

3. The flow direction of the medium is not restricted, and the flow is not disturbed and the pressure is not reduced.

 

4. The shape is simple, the structure length is short, the manufacturing process is good, and the application range is wide.

 

The disadvantages of gate valves are as follows:

 

1. It is easy to cause erosion and abrasion between the sealing surfaces, and it is difficult to maintain.

 

2. The overall size is large, and a certain space is required for opening, and the opening and closing time is long.

 

3. The structure is more complex.

 

Attention should be paid to the following matters in the installation and maintenance of gate valves: 1. Handwheels, handles and transmission mechanisms are not allowed to be used for lifting, and collisions are strictly prohibited. 2. The double gate gate valve should be installed vertically (i.e., the stem is in a vertical position and the handwheel is at the top). 3. The gate valve with bypass valve should be opened before opening (to balance the pressure difference between the inlet and outlet and reduce the opening force). 4. The gate valve with transmission mechanism shall be installed according to the provisions of the product instruction manual. 5. If the valve is used frequently, lubricate it at least once a month.

 

Characteristics of elastic seat seal gate valve: for a long time, the general gate valve used in the market generally has water leakage or rust, the company introduced European high-tech rubber and valve manufacturing technology to produce the elastic seat seal gate valve, to overcome the general gate valve poor sealing, rust and other defects, elastic seat seal gate valve uses the elastic gate plate to produce a small amount of elastic deformation compensation effect to achieve a good sealing effect, the valve has the significant advantages of light switch, reliable sealing, good elastic memory and service life.