Working characteristics of pipeline ball valve: 1. Basi […]
Working characteristics of pipeline ball valve:
1. Basic structure
General ball valves for natural gas pipelines are mainly composed of valve body, valve seat, ball, valve stem and transmission device. The main function of the ball valve is to connect and cut off the fluid channel in the pipeline. The ball valve is used to rotate the ball 90 ° through the transmission device to achieve the opening and closing functions.
Commonly used natural gas pipeline ball valves mainly have two types of floating ball structure and fixed ball structure.
① The ball of the floating ball valve can float. Under the pressure of natural gas, the ball will be pressed tightly to the seal ring on the outlet side. This will form a single seal, and the sealing of the valve seat in front of the valve cannot be guaranteed. The ball valve of this structure is characterized by a simple structure and good one-side sealing performance, but its sealing surface bears a large pressure, so the opening and closing force is huge.
② The ball of the fixed structure ball valve has upper and lower rotating shafts, the lower rotating shaft is fixed on the bearing at the lower part of the valve body, and the upper part is connected to the valve stem. The ball can rotate along an axis perpendicular to the valve channel, and the ball cannot move sideways like a floating structure ball valve. Therefore, when the fixed ball valve is in operation, the pressure of the fluid in front of the valve is only transmitted to the bearing and the stem, and does not cause pressure on the valve seat. Therefore, the fixed ball valve has low torque, small deformation of the seat, stable sealing performance, and long service life. The valve seat of the fixed ball valve is floating, and the floating valve seat presses the ball body by the pressure of the spring behind the valve seat and the pressure of the natural gas, thereby achieving sealing.
2. Valve seat structure of ball valve
The most commonly used ball valves in domestic natural gas pipelines are CAMERON ball valves, GROVE ball valves, and the most commonly used valve seat structures have the following forms.
(1) Ordinary valve seat
Ordinary valve seats are generally used on ball valves with a diameter of less than 200mm floating valve seats. Ordinary valve seat is mainly under the preload force or the pressure of the fluid, the valve seat and the ball are compressed, and the valve seat material is plastically deformed to achieve the seal, the sealing effect depends on the valve seat under the action of the fluid or preload Under the action of force, it can compensate the degree of sphericity and microscopic unevenness of the surface. The valve seat has a simple structure, is easy to manufacture and manufacture, and is widely used.
(2) Elastic valve seat
There are relatively many forms of elastic seats, but commonly used in natural gas pipelines are coil spring seats and disc spring seats. These two seats are the elastic force of the spring and the pressure of the fluid to push the seat to the ball, so as to achieve seal. These two valve seats have good bidirectional sealing ability and good elasticity compensation ability, but for the coil spring group valve seat, it is difficult to achieve the same rigidity of each spring, so that the valve seat is unevenly affected The sealing performance of the valve. In contrast, the disc spring is simple, compact, easy to process, and evenly stressed. Therefore, it is widely used.
(3) Rotating valve seat
The crescent-shaped narrow channel is formed between the ball and the valve seat at the moment of opening or closing of the ball valve, so the natural gas is throttled to a high-speed surge turbulent state, which often causes the valve seat to be eroded and internal leakage occurs. The main feature of the rotary valve seat is that the valve seat can rotate along the axis of the channel during the opening and closing of the valve. By turning the valve on and off, the valve seat can be rotated to make the valve seat wear evenly in the circumferential direction, improve the working condition, and extend the service life.