Issues to pay attention to when using manual valves

Manual valves are control components in fluid transport systems, used to change the cross-section of the passage and the flow direction of the medium. They have functions such as guiding flow, shutting off, regulating, throttling, preventing backflow, diverting, or relieving pressure. Valves used for fluid control have nominal diameters ranging from very small instrument valves to industrial pipeline valves with diameters up to 10m.

I. Opening and closing of manual valves:

1. Manual valves are the most widely used valves. Their handwheels or handles are designed for ordinary human strength, taking into account the strength of the sealing surface and the necessary closing force. Therefore, long levers or wrenches should not be used to operate them. Some people are accustomed to using wrenches; it is important to be careful not to apply excessive force, as this can easily damage the sealing surface or break the handwheel or handle.

2. When opening and closing the valve, the force should be steady and not abrupt. Some high-pressure valves designed for impact opening and closing have components that consider this impact force, which cannot be equated with general valves.

3. For steam valves, preheat before opening and eliminate condensate. When opening, do so gently to avoid water hammer.

4. After the valve is fully open, slightly turn the handwheel in reverse to tighten the threads to prevent loosening and damage. For rising stem valves, remember the stem position when fully open and fully closed to avoid hitting the dead point when fully open. This also facilitates checking whether it is normal when fully closed. If the valve falls off or if large debris is embedded between the valve core seals, the stem position when fully closed will change.

5. When the pipeline is first used, there may be a lot of dirt inside. The valve can be slightly opened to use the high-speed flow of the medium to flush it out, then gently close it (do not close quickly or forcefully to prevent residual impurities from damaging the sealing surface), and open it again. Repeat this several times to flush out the dirt before putting it into normal operation.

6. For normally open valves, dirt may stick to the sealing surface. When closing, use the above method to flush it clean before officially sealing it.

7. If the handwheel or handle is damaged or lost, it should be replaced immediately. Do not use adjustable wrenches as substitutes to avoid damaging the square of the valve stem, which can lead to operational difficulties and accidents during production.

8. For certain media, after the manual valve is closed and cools, the valve components may contract. The operator should close it again at an appropriate time to ensure that there are no small gaps in the sealing surface; otherwise, the medium flowing through the small gap at high speed can easily erode the sealing surface.

9. During operation, if it is found that the operation is too strenuous, the cause should be analyzed. If the packing is too tight, it can be appropriately loosened. If the valve stem is misaligned, personnel should be notified for repair. Some valves, when in the closed state, have the closing components expand due to heat, making it difficult to open. If it must be opened at this time, the valve cover threads can be loosened half a turn to a full turn to relieve the stem stress, and then the handwheel can be operated.

II. Precautions:

1. For high-temperature valves above 200℃, since they are installed at room temperature and the temperature rises during normal use, the bolts expand due to heat, increasing the gap. Therefore, they must be tightened again, known as "thermal tightening." Operators should pay attention to this work; otherwise, leaks may easily occur.

2. In cold weather, if water valves are closed for a long time, the water behind the valve should be drained. After steam valves stop steaming, condensate should also be drained. If there is a drain plug at the bottom of the valve, it can be opened to drain water.

3. Non-metallic valves may be hard and brittle or have lower strength. When operating, the opening and closing force should not be too great, especially not with excessive force. Care should also be taken to avoid collisions with objects.

4. When using new manual valves, the packing should not be compressed too tightly, just enough to prevent leakage, to avoid excessive pressure on the valve stem, which can accelerate wear and make opening and closing difficult.