Hand-operated valve is a widely used valve in equipment and devices, operated by handle or hand wheel. Generally, clockwise rotation of the handle or hand wheel is the designated closing direction, and counterclockwise rotation is the designated opening direction. However, some valves have opposite opening and closing directions, so it is necessary to check the opening and closing symbols before operation.
Therefore, it is stipulated that lever or long wrench cannot be used to open and close valves. Only one person is allowed to operate the handle with length of less than 320mm, while a hand wheel with a diameter equal to or greater than 320mm can be operated by two persons or one person with an appropriate lever (generally no longer than 0.5m). However, diaphragm valves and non-metallic valves are strictly prohibited from using levers or long wrenches, and it is not allowed to close the valve with excessive force.
Some operators are accustomed to using levers and long wrenches to operatehand-operated valves, thinking that the greater the closing force, the better. However, this will cause premature damage to the valve, or even accidents. Practice has proved that it is easy to damage the hand wheel, handle, scratch the valve stem and sealing surface, or even crush the sealing surface when the valve is closed with excessive force, except for the impact hand wheel. Furthermore, when the hand wheel or handle is damaged or lost, it should be replaced in time and cannot be replaced with an adjustable wrench.
When valves like gate valve and globe valve are closed or opened to the end (i.e., bottom dead point or top dead point), they should be turned back 1/4 to 1/2 circle to get better thread sealing, in order to facilitate operation and avoid damage to the valve from overtightening. For larger caliber butterfly valves, gate valves and globe valves, some are equipped with bypass valves. The function of the bypass valve is to balance the inlet and outlet pressure difference and reduce the opening torque. When opening, the bypass valve should be opened first and then the main valve. The pipeline must be preheated and the condensation water should be discharged before opening the steam valve. The opening process should be slow in order to avoid water hammer phenomenon and damage to the valve and equipment.
When opening and closing a ball valve, butterfly valve or plug valve, the valve is fully open when the groove on the top of the valve stem is parallel to the channel; the manual valve is fully closed when the groove on the top of the valve stem is vertical to the channel after rotating 90 degrees either to the left or right. Some ball valves, butterfly valves and plug valves are opened with the wrench parallel to the channel and closed with the wrench vertical to the channel. The operation of three-way and four-way valves should follow the markings for opening, closing or changing direction, and the operating handle should be removed after the operation is completed. For gate valves and throttle valves with markings, the indicated position for fully open or fully closed should be properly adjusted. The position of fully open and fully closed for rising stem gate valves and globe valves should also be remembered to avoid hitting the dead point when fully open. When the valve is fully closed, leakage or foreign objects can be found by using a ruler or marker, so as to troubleshoot problems.
The internal walls of newly installed pipelines and equipment often contain a lot of dirt and welding slag. It is easy for the sealing surface of the hand-operated valve that is often kept open to be contaminated with dirt, making it necessary to use the small opening method to allow the high-speed medium to flush away these impurities before gently closing. For some hand-operated valves, the valve element may shrink and cause minor gaps on the sealing surface, leading to leakage when the temperature drops after closing. Therefore, the valve should be closed again after an appropriate period of time after the first closing.
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