Detailed methods for correct operation of valves

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

Preparation before operation

Before operating the valve, read the operation 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 if the valve is affected with moisture. If it is affected with moisture, dry it; If any other problem is found, it should be dealt with in time and no fault operation is allowed. If the electric valve has been out of service for more than 3 months, the clutch should be checked before starting. After confirming that the handle is in the manual position, the insulation, steering and electrical circuit of the motor should be checked.

Correct operation of manual valve

Manual valve is the most widely used valve, its hand wheel or handle is designed according to ordinary manpower, taking into account the strength of the sealing surface And the necessary closing force. Therefore, it is not allowed to use long lever or long spanner to move the valve. Some people are used to using spanner, so they should pay attention to it strictly. When opening the valve, the force should be stable to avoid excessive force, resulting in the opening and closing of the valve. The force should be stable and can not be impacted. This impact force has been considered for all parts of some high-pressure valves with impact opening and closing, which is not equal to that of general valves.
When the valve is fully opened, the handwheel should be turned back a little to make the threads tight, so as to avoid loosening and damage. For rising stem valve, remember the position of the stem when it is fully opened and fully closed, so as to avoid hitting the top dead center when it is fully opened. It is also convenient to check whether it is normal when it is fully closed. If the valve does fall off, or there are large impurities embedded between the valve core seals, the position of the stem will change when it is fully closed. The sealing surface of the valve or valve handwheel damage.
Valve opening mark: when the groove on the top surface of the valve stem 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 stem rotates 90 to the left or right, 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 are opened when the wrench is parallel to the channel, and closed when the wrench is vertical. The operation of three-way and four-way valves should be carried out according to the marks of opening, closing and reversing. After the operation, the movable handle should be removed.

Correct operation of safety valve

The safety valve has undergone pressure test and constant pressure before installation. When the safety valve operates for a long time, the operator should pay attention to check the safety valve. When checking, the operator should 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, open it once at intervals, remove the dirt and verify the flexibility of the safety valve.

Correct operation of steam trap

The drain valve is easy to be blocked by water and other impurities. When it is used, first open the flushing valve and flushing pipe. If there is a bypass pipe, open the bypass valve for short flushing. If there is no flushing pipe and bypass pipe, remove the drain valve, open the shut-off valve after flushing, install the drain valve, and then open the shut-off valve to start the drain valve.

Correct operation of pressure reducing valve

Before the pressure reducing valve is put into operation, the bypass valve or flushing valve should be opened to clean the dirt in the pipeline. After the pipeline is washed clean, the bypass valve and flushing valve should be closed, and then the pressure reducing valve should be started. Some steam pressure reducing valves have steam traps in front of them, which need to be opened first, then the shut-off valve behind the pressure reducing valve should be slightly opened, and finally the shut-off valve in front of the pressure reducing valve should be opened. Watch the pressure gauges before and after the pressure reducing valve, and adjust the regulating screw of the pressure reducing valve After that, slowly open the shut-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.
If the pressure reducing valve fails or needs to be repaired, the bypass valve should be opened slowly first, and the shut-off valve in front of the valve should be closed at the same time. The bypass valve should be adjusted roughly by hand, so that the pressure behind the pressure reducing valve is basically stable at the predetermined value, and then the pressure reducing valve should be closed. After replacement or repair, it can return to normal.

Correct operation of check valve

In order to avoid the high impact force formed at the moment when the check valve is closed, the valve must be closed quickly, so as 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 in a large range, the minimum velocity is not enough to force the closing part to stop stably. In this case, the movement of the closing part can be restrained by a damper within a certain range of its action stroke. The rapid vibration of the closing part will make the moving part of the valve wear If the medium is pulsating flow, the rapid vibration of the closing part is also caused by the extreme medium disturbance. In this case, the check valve should be placed at the place with the minimum medium disturbance.

Source: China Valve Supplier: www.epowermetals.com

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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