Manual valves are a type of valve commonly used on equipment and devices that are operated by handles and handwheels. Under normal circumstances, the handle and the handwheel are rotated in the direction of the closing direction, and the counterclockwise rotation is defined as the opening direction. However, some valves open and close in the opposite direction to the above, and should focus on checking the opening and closing signs before operation.
For manual valves, the handle and handwheel are designed to be normal. Therefore, it is stipulated in the use of the valve that the operator is not allowed to open and close the valve by means of a lever and a long wrench. At the same time, the length of the handle and the diameter of the hand wheel are less than 320mm, and only one person is allowed to operate; the hand wheel with a diameter equal to or exceeding 320mm allows the two to operate together, or allows one person to operate with the appropriate lever (the general length does not exceed 0.5m). However, diaphragm valves and non-metallic valves are strictly prohibited to operate with levers or long wrenches, and they do not require excessive and excessive force to close the valve.
Some operators are accustomed to using a lever and a long wrench to operate the manual valve. It is considered that the greater the closing force, the better. This can cause premature failure of the valve and even cause an accident. Practice has confirmed that in addition to the impact type handwheel, excessively large and excessively operating the valve easily damages the hand wheel, the handle, scratches the valve stem and the sealing surface, and even crushes the sealing surface. Secondly, after the handwheel and handle are damaged or lost, they should be timely provided and the utility model should not be used.
Valves such as gate valves and globe valves should be turned 1/4~1/2 turn when closing or opening to the head (ie, bottom dead center or top dead center), so that the threads are better tightly closed to facilitate inspection during operation to avoid screwing. It is too tight to damage the valve. Larger diameter butterfly valves, gate valves and globe valves, and some with bypass valves. The function of the bypass valve is to balance the differential pressure between the inlet and outlet and reduce the opening torque. When opening, open the bypass valve before opening the large valve.
Before opening the steam valve, the pipe must be preheated to discharge the condensed water. Be slow when opening to avoid water hammer and damage to valves and equipment. When the ball valve, butterfly valve or plug valve is opened and closed, when the groove on the top surface of the valve stem is parallel to the passage, it indicates the full open position of the valve; when the valve stem is rotated 90 degrees to the left or right, when the groove is perpendicular to the passage, Indicates that the valve is in the fully closed position. Some ball valves, butterfly valves, and plug valves are opened in parallel with the wrench and closed vertically. The operation of the three-way and four-way valves shall be carried out according to the markings of opening, closing and reversing. After the operation, the movable handle shall be removed.
For the gate valve and throttle valve with the mark, check the position of the fully open or fully closed indicator. The open gate valve and the shut-off valve should also be used in their fully open and fully closed positions, so as to avoid the top dead center when fully open. When the valve is fully closed, the ruler and the mark can be used to find that the closing piece is detached or against the foreign object, so as to eliminate the malfunction. Newly installed pipes and equipment, there are many dirt, soldering, etc. inside. The normally open manual valve sealing surface is easily stuck with dirt, and the micro-opening method is applied to allow the high-speed medium to wash away the foreign matter, and then gently close. Some manual valves are closed, the temperature drops, and the valve member contracts, causing small gaps in the sealing surface and leakage. This should be turned off again at the appropriate time after shutdown. Whether the valve is operated correctly or not directly affects the service life of the valve.