Natural gas pipelines basically use fixed-shaft forged steel ball valves, which generally use flange connections or butt welding connections.

Since the natural gas transported by long-distance pipelines cannot be clean, the pipelines need to be cleaned regularly, and the reliability of the seal is required to be ensured during a long service period. Therefore, a combined seal seat was designed to meet this functional requirement.

At present, fixed shaft ball valves usually have two valve seat designs: one is a downstream valve seat self-relieving design; the other is a double-piston effect design. Both have a double cut-off sealing effect.

The ball adopts a fixed structure and a floating valve seat, which can achieve a smaller torque under operating pressure. It uses a metal bushing with self-lubricating PTFE, which cooperates with a high-strength, high-finish valve stem to minimize the friction coefficient. The sealing seat is spring-loaded and has excellent sealing performance within a wide range of temperature changes and pressure changes, ensuring a seal without bubble leakage under the closing pressure difference, and maintaining the minimum operating torque under the maximum pressure difference.

When the valve with downstream self-relief function is in the closed state, the pipeline pressure acts on the outer surface of the upstream valve seat ring, causing the valve seat ring to press against the ball. If the medium leaks from the upstream valve seat into the valve cavity, when the pressure in the valve cavity exceeds the downstream pipeline pressure, the downstream valve seat will break away from the ball and the pressure in the valve cavity will be released downstream of the valve. This is a ball valve with a self-protection mechanism that protects the valve itself from damage due to overpressure.

Under normal circumstances, for pipeline ball valves with double piston effect design (DPE), pressure acts on the outside of the end of the valve seat sealing ring. This force forces the valve seat sealing ring to be squeezed closer to the valve body, thereby causing a gap between the valve seat sealing ring and the valve. A seal is formed between the bodies.

If the valve seat leaks, the pressure will directly enter the inside of the valve body. This pressure will act on the inside of the upstream sealing surface of the valve seat sealing ring and tightly squeeze the upper part of the valve seat sealing ring. At the same time, this force will force the valve seat sealing ring to be squeezed closer to the valve body, thereby forming an effective seal between the valve seat sealing ring and the valve body.

In actual production, due to improper maintenance of DPE ball valves or improper design specifications or selected sealing ring materials of some DPE ball valves, the excellent sealing design of DPE has become one of the main reasons for ball valve locking. Therefore, pay attention to regular maintenance of ball valves. Injecting a certain amount of grease to soak the valve can effectively prevent the valve seat and ball from locking, and can also remove sand, garbage and dust in the pipeline.