The reasons for the internal leakage of the valve during the construction period: improper transportation and hoisting caused overall damage to the valve and then constituted the internal leakage of the valve; when leaving the factory, the valve was not dried and anti-corrosive after the water pressure was pressed, which constitutes the rust of the sealing surface and constitutes the internal leakage; The protection of the construction site is not in place, and the two ends of the valve are not equipped with blind plates, and impurities such as rainwater and sand enter the valve seat, which constitutes leakage; during the installation, no grease is injected into the valve seat, causing impurities to enter the rear of the valve seat, or burns during welding Internal leakage.
The valve is not installed in the fully open position, causing damage to the ball. During welding, if the valve is not in the fully open position, welding spatter will cause damage to the ball. When the ball with welding spatter is switched on and off, it will further cause damage to the valve seat. Then lead to internal leakage; welding slag and other construction leftovers constitute a scratch on the sealing surface; inaccurate limit during delivery or installation constitutes leakage. If the valve stem drive sleeve or other accessories are misplaced with the installation viewpoint, the valve will leak.
Reasons for internal leakage of valves during operation: The most common reason is that the operators do not protect the valves in consideration of the relatively expensive protection costs, or the lack of scientific valve management and protection methods does not provide preventive protection to the valves, which constitutes equipment early There is a fault; improper operation or failure to protect in accordance with the protection procedures constitutes internal leakage; during normal operation, construction leftovers scratch the sealing surface and constitute internal leakage; improper pigging constitutes damage to the sealing surface and constitutes internal leakage.
If the valve is not maintained or moved for a long time, the valve seat and the ball will be locked, which will cause seal damage and internal leakage when the valve is switched on and off; the valve will not be switched in place to cause internal leakage. Any ball valve will generally be skewed by 2°~3 regardless of the open or closed position. °It may cause leakage; many large-caliber ball valves mostly have stem stop blocks. If they are used for a long time, rust, dust, paint and other debris will accumulate between the stem and stem stop blocks due to rust and other reasons.
These debris will make the valve unable to rotate in place and cause leakage - if the valve is buried, lengthening the stem will cause more rust and impurities to prevent the valve ball from rotating in place, causing the valve to leak, and general actuators are also limited If there is corrosion for a long time, the hardening of the grease or the loosening of the limit bolts will make the limit inaccurate and constitute an internal leakage; the valve position of the electric actuator is set forward, and the internal leakage is not closed in place.
Lack of periodic protection and maintenance will cause the sealing grease to dry and harden. After the dried sealing grease accumulates on the elastic valve seat, the valve seat is prevented from moving and the seal fails. Fixed shaft ball valves are commonly used in natural gas pipelines. The general inspection method is: turn the valve to the fully open or fully closed position, and check whether there is leakage through the discharge of the valve body's drain nozzle. If it can be cleaned, the sealing is excellent. If the pressure has been discharged, it can be considered that the valve is leaking, and the valve must be treated accordingly.