**Manual Valve Operation Instructions**
After installing a manual valve, the operator must thoroughly understand its structure and functionality. It is essential to be able to clearly identify which direction corresponds to opening and which to closing. Proper operation of the manual valve directly affects the valve’s service life and the performance of the equipment it is installed in.
The most common type of manual valve is operated using a handle. Typically, rotating the handle clockwise closes the valve, while counterclockwise opens it. However, some valves may have the opposite action, so it's crucial to check the valve's markings before operation to avoid mistakes.
The handle is designed for normal human force, so using a lever or excessive force is strictly prohibited. For handwheels with a diameter less than 320mm, one person can operate the valve. If the diameter is larger than 320mm, two people should work together. Diaphragm valves, pinch valves, and other non-metallic valves must not be operated with a lever, and they should not be forced shut, as this could cause damage.
Gate and globe valves require careful operation. When fully opened or closed, these valves should be returned by half a turn or one full revolution. This helps maintain thread integrity and makes future inspections easier, preventing over-tightening that might damage the valve.
For larger butterfly, gate, and globe valves—especially those without bypass valves—it is important to preheat the pipeline and balance the pressure difference between the inlet and outlet. This reduces the force needed to open the valve. When opening, first open the bypass valve to equalize the pressure, then proceed with opening the main valve. When closing, close the bypass valve first, then the main valve.
When operating steam valves, the pipeline must be preheated to remove condensate. Closing the valve too quickly can cause water hammer, which may damage both the valve and the equipment. Always close the valve slowly.
For brake valves and throttle valves, it is important to check the fully open or fully closed positions. This prevents the valve from hitting the dead point when fully open. When closing, use the scale or markings on the valve to detect if the closure mechanism has become detached or is obstructed by foreign objects. If this occurs, it should be addressed immediately to prevent malfunctions.
When opening ball, butterfly, or plug valves, the groove on the top of the stem should align with the channel to indicate a fully open position. Rotating the stem 90 degrees to the left or right will align the groove perpendicular to the channel, indicating a fully closed position. Some valves use color-coded or marked indicators to show the open and closed positions.
Throttle and stop valves should never be used for throttling. Doing so can erode the sealing surfaces and lead to premature failure of the valve.
Newly installed pipelines, equipment, and valves often contain debris such as slag or welding residue. These particles can get stuck on the sealing surfaces of normally open valves. To clean them, use a micro-closing method: briefly open the valve to allow the high-speed medium to flush out the debris, then slowly open it fully. Repeat this process several times until the valve is clean.
In some cases, when a valve is closed, temperature drops can cause parts to contract, creating small gaps in the sealing surface and leading to leaks. To prevent this, after closing the valve, it is recommended to re-close it slightly at an appropriate time. This ensures a tighter seal and avoids potential leakage issues.
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