As we all know, a gate is the opening and closing part of the cast steel gate valve. The movement direction of the gate is perpendicular to the direction of the fluid. The gate valve can only be fully opened and closed, but cannot be adjusted or throttled.
1. Gate of cast steel gate valve
The gate has two sealing surfaces. The most common model gate valves have two sealing surfaces that form a wedge. The wedge angle varies with the valve parameters, which is usually 50° and 2°52′ under moderate medium temperatures. At the same time, the valve is often opened and closed during the use of a cast steel gate valve. Also, there is internal wear over time. Therefore, connection failures between the valve stem and the valve core will sometimes cause the valve core to fall off.
Cast steel valves cannot be opened after they are closed since they can only be replaced after cut out of the system. If they cannot be cut out of the system, you should use alternative processes or devices to stop them.
2. Valve core of the cast steel gate valve
When the valve core of the cast steel gate valve falls off and cannot be cut out, you can change the assembly method of the valve cover, valve stem, copper sleeve, coil and gland while keeping the valve body, valve core and valve seat under the condition that the valve core has been sealed by the airtight medium to expose the valve core. Then, you can connect the valve stem and the valve core in a common way so that cast steel valves remain sealed in three places and reopen.
After the valve cover of the cast steel gate valve is removed, the wedge angle of the valve core is within the friction angle range except for special cast steel valves. No matter how the pressure on the two ends of the valve core changes, the valve core will not be extruded from the valve seat by itself under the self-locking condition, and there is no extrusion for the flat valve core.
If the connection between the valve stem and the valve core of the cast steel gate valve fails, the handwheel can still be rotated. You can push the valve core back into the valve seat by the handwheel to ensure a tight sealing between the two sealing surfaces, which is a premise for applying this repair method. Then, you need to loosen the packing set by unscrewing the gland nut, and loosening the nuts on all bolts on the valve cover in turn.
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