The valve is a device used to control the direction, pressure and flow of fluid in the fluid system, which can make the medium (liquid, gas, powder) in the piping and equipment flow or stop and control its flow. The valve is an important control part in the fluid transportation system.



Preparation before operation


Before operating the valve, read the operating instructions carefully. Before operation, be sure to know the flow direction of the gas, and pay attention to check the opening and closing signs of the valve. Check the appearance of the valve to see whether it is damped. If it is damped, dry it; if it is found that there are other problems, handle them in time and do not operate with faults. If the electric valve has been out of service for more than 3 months, check the clutch before starting. After confirming that the handle is in the manual position, check the insulation, steering and electrical circuit of the motor.

Correct operation of manual valve



Manual valve is the most widely used valve. Its handwheel or handle is designed according to common manpower, considering the strength of sealing surface and necessary closing force. Therefore, it is not allowed to move with long lever or long wrench. Some people are used to using the wrench, so they should pay strict attention to it. When opening the valve, they should use steady force to avoid excessive force, which will cause the opening and closing of the valve. The force should be stable and not be impacted. Some parts of high-pressure valves with impact opening and closing have considered the impact force and general valve can not be equal to each other.


When the valve is fully opened, turn the hand wheel back a little, so that the threads are tight to avoid looseness and damage. For open stem valves, remember the valve stem position when fully open and fully closed to avoid hitting the top dead center when fully open. It is convenient to check whether it is normal when it is fully closed. If the valve office falls off, or a large sundry is embedded between the valve core seals, the valve stem position will change when the valve is fully closed. Damage to valve sealing surface or valve handwheel.



Valve opening mark: when the groove on the top surface of the valve rod of ball valve, butterfly valve and plug valve is parallel to the channel, it indicates that the valve is in the full open position; when the valve rod rotates 90 to the left or right. When, the groove is perpendicular to the channel, indicating that the valve is in the fully closed position. Some ball valves, butterfly valves and plug valves open when the wrench is parallel to the channel, and close when the wrench is vertical. The three-way and four-way valves shall be operated according to the marks of opening, closing and reversing. Remove the movable handle after operation.



Correct operation of safety valve


The safety valve has undergone pressure test and constant pressure before installation. When the safety valve runs for a long time, the operator shall pay attention to the inspection of the safety valve. During the inspection, the operator shall avoid the outlet of the safety valve, check the lead seal of the safety valve, pull up the safety valve with a wrench by hand, and open it once in a period of time to discharge the dirt and check the flexibility of the safety valve.



Correct operation method of drain valve


Drain valve is easy to be blocked by water pollution and other sundries. When it is used, first open the flushing valve and flush the pipeline. If there is a bypass pipe, the bypass valve can be opened for short flushing. For the drain valve without flushing pipe and bypass pipe, the drain valve can be removed. After opening the shut-off flushing, close the shut-off valve, install the drain valve, and then open the shut-off valve to enable the drain valve.



Correct operation of pressure reducing valve


Before the pressure reducing valve is opened, the bypass valve or flushing valve shall be opened to clean the dirt in the pipeline. After the pipeline is cleaned, the bypass valve and flushing valve shall be closed, and then the pressure reducing valve shall be opened. Some steam pressure reducing valves have drain valves in front of them, which need to be opened first, then slightly open the cut-off valve behind the pressure reducing valve, finally open the cut-off valve in front of the pressure reducing valve, watch the pressure gauge in front of and behind the pressure reducing valve, adjust the regulating screw of the pressure reducing valve to make the pressure behind the valve reach the predetermined value, then slowly open the cut-off valve behind the pressure reducing valve, and correct the pressure behind the valve until it is satisfied. Fix the adjusting screw and cover the protective cap.

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If the pressure reducing valve fails or needs to be repaired, the bypass valve shall be opened slowly, and the front shut-off valve shall be closed at the same time. The bypass valve shall be adjusted roughly by hand, so that the pressure behind the pressure reducing valve is basically stable above and below the predetermined value, and then the pressure reducing valve shall be closed for replacement or repair before it returns to normal.


Correct operation of check valve


In order to avoid the high impact force at the moment when the check valve is closed, the valve must be closed quickly to prevent the formation of a great backflow speed, which is the reason for the formation of impact pressure when the valve is suddenly closed. Therefore, the closing speed of the valve should be correctly matched with the attenuation speed of the downstream medium.


If the velocity of the downstream medium varies widely, the minimum velocity is not enough to force the closure to stop stably. In this case, the motion of the closing member can be restrained by a damper within a certain range of its action stroke. The fast vibration of the closing parts will cause the valve moving parts to wear too fast, leading to premature failure of the valve. If the medium is pulsating flow, the fast vibration of the closing part is also caused by extreme medium disturbance. In any case, the check valve should be placed at the place with the least medium disturbance.