Is there a practice for operating valves that involves turning them all the way open and then turning them back a little?

I’ve heard that claim before. My understanding is that it takes into account the thermal expansion and contraction of metals due to temperature changes, in order to prevent the transmission mechanism from \"locking up\" and affecting valve closure. For reference only!

There is a theory that, in addition to the issues mentioned above, another reason is that if the valve is closed so tightly every time, over time this can cause the seal of the valve or the metal components inside it to become deformed, leading to internal leakage of the valve. This kind of situation happens frequently in factories.

It can’t be generalized; only in the case of electric doors where such a requirement exists. Using manual valves in this situation can easily lead to leaks at the sealing surfaces. We have encountered many such problems on site; the operators are not familiar with the proper procedures for operation, which leads to the premature failure of the valves and results in a significant waste of resources.

Indeed, this is what is said on site; manual operation is the most widely used method. Its handwheel or handle is designed based on human strength, taking into account the strength of the sealing surface and the necessary closing force. Therefore, it cannot be turned using a long lever or long wrench. Some people are used to using wrenches; it is essential to be careful not to apply too much force, as this can easily damage the sealing surfaces or even break the wrench. After fully opening it, the handle should be turned slightly in the opposite direction to ensure a tight fit between the threads, thereby preventing loosening and damage. For straight-stem valves, remember the position of the stem when the valve is fully open and fully closed, to avoid hitting the dead center when it is fully open.

This post was last edited by New designer on 2010-3-19 at 13:27. If the operations prove to be too difficult, the reasons should be analyzed. If the packing is too tight, it can be loosened slightly; if the valve stem is skewed, personnel should be notified for repair. In some valves, when they are closed, the closing element expands due to heat, making it difficult to open them ； If it must be opened at this time, loosen the valve cover threads by half a turn to one full turn to relieve stress on the valve stem, and then turn the handwheel.

There indeed is such a saying. The main reason is that if the valve is closed all the way every time, it will cause damage to the valve’s sealing surfaces over time, leading to internal leakage of the valve. In factories, experienced workers or machine operators often encounter this problem.

There is indeed such a saying; it stems from hands-on experience in the field and is generally not emphasized. This applies to the valves in thermal systems when operating them.

I heard that it is necessary to turn it all the way and then reverse the rotation once; otherwise, when the workers on the next shift check this valve, they will assume it is closed (since the valve locks itself when turned to the point where it can no longer be moved, which may lead them to think it is closed), resulting in incorrect operations. I’m not sure if this claim is valid.

This statement applies only to gate valves; globe valves cannot be operated in this way. The sealing of a gate valve is achieved through radial contact between the gate and the sealing surface of the valve seat. When the gate valve is closed, the handwheel drives the valve stem to lower the gate until it makes contact with the valve seat sealing surface; once full contact is established, sealing is achieved. \"Turning it back a notch\" takes advantage of the gap at the connection between the valve stem and the gate – too much rotation should be avoided, as this could lift the gate again and disrupt the seal. In the case of wedge-shaped elastic gate valves, when there is slight wear or clearance on the sealing surface, \"adjusting it back by one notch\" can affect the sealing performance. The sealing of a globe valve is achieved through the axial contact between the valve stem and the sealing surface of the valve seat; the degree of this contact affects the sealing performance. The valve stem must continuously apply force to the valve stem, and if there is a \"backlash,\" this force will be reduced, thereby affecting the sealing effect.

How do I reset an electric door? Furthermore, turning a manual valve to the full open position and then turning it back slightly can cause leakage at the sealing surface – why is that?