Manual valve is a kind of valve commonly used in equipment and devices, which is operated by handle and handwheel. Under normal circumstances, the clockwise rotation of the handle and handwheel is specified as the closing direction, and the counterclockwise rotation is specified as the opening direction. However, the opening and closing direction of some valves is opposite to the above, so you should pay attention to checking the opening and closing signs before operating.
Manual valve, the size of its handle and hand wheel is designed according to normal manpower. Therefore, it is stipulated in the use of the valve that the operator is not allowed to open and close the valve with the help of a lever and a long wrench. At the same time, if the length of the handle and the diameter of the handwheel are less than 320mm, only one person is allowed to operate; Handwheels with a diameter equal to or exceeding 320mm allow two people to operate together, or allow one person to operate with an appropriate lever (generally the length does not exceed 0.5m). However, diaphragm valves and non-metallic valves are strictly prohibited from using levers or long wrenches to operate, and it is also not allowed to use excessive force to close the valve.
Some operators are accustomed to using levers and long wrenches to operate manual valves, thinking that the greater the closing force, the better. In fact, this is not the case. This can cause premature valve damage and even lead to accidents. Practice has proved that, except for the impact handwheel, operating the valve with excessive force will easily damage the handwheel, handle, scratch the valve stem and sealing surface, and even crush the sealing surface. Secondly, when the handwheel and handle are damaged or lost, they should be assembled in time, and it is not allowed to use a live wrench instead.
Valves such as gate valves and globe valves should be turned 1/4 to 1/2 turn when they are closed or opened to the end (ie, bottom dead center or top dead center), so that the threads can be better sealed, which is convenient for inspection during operation, so as not to damage the valve by over-tightening.
Larger diameter butterfly valves, gate valves and globe valves, and some are equipped with bypass valves. The function of the bypass valve is to balance the pressure difference between the inlet and outlet and reduce the opening torque. When opening, the bypass valve should be opened first, and then the large valve should be opened.
Before opening the steam valve, the pipeline must be preheated to drain the condensed water. Open slowly to avoid water hammer and damage to valves and equipment.
When opening and closing ball valves, butterfly valves and plug valves, when the groove on the top surface of the valve stem is parallel to the channel, it indicates that the valve is in the fully open position; when the valve stem is rotated 90 degrees to the left or right, and the groove is perpendicular to the channel, it indicates that the valve is in the fully closed position. Some ball valves, butterfly valves and plug valves are opened when the wrench is parallel to the channel, and closed when they are vertical. The operation of the three-way and four-way valves should be carried out according to the marks of opening, closing and reversing, and the movable handle should be removed after the operation.
For gate valves and throttle valves with scales, check and adjust the fully open or fully closed indicating position. For the rising stem gate valve and globe valve should also remember their fully open and fully closed positions, so as to avoid hitting the dead point when fully open. When the valve is fully closed, with the help of the scale and mark it can be found that the closing piece falls off or resists foreign objects, so as to troubleshoot.
There are a lot of dirt, welding slag, etc. on the inner surface of the newly installed pipes and equipment. The sealing surface of the normally open manual valve is easy to stick to dirt, and the slightly open method should be used to allow the high-speed medium to wash away these foreign objects, and then gently close.
After some manual valves are closed, the temperature drops and the valve parts shrink, causing small gaps on the sealing surface and leakage. This should be closed again at an appropriate time after closing.
Whether the valve is operated correctly or not directly affects the service life of the valve.