Must-see valve knowledge


For the newly designed and installed control system, in order to ensure that the regulating valve can work normally when starting up and make the system operate safely, before installing the new valve, check whether the nameplate on the valve conforms to the design requirements. The following items should also be debugged. Basic error limit; full stroke deviation; hysteresis; dead zone; leakage (in the case of strict requirements). If the control valve in the original system is overhauled, in addition to checking the above items, the packing box and joints of the old valve should also be checked for tightness.

1. Flange sealing and leakage sealing treatment method

There are many factors that affect flange sealing. Mainly include: bolt preload; sealing surface type; gasket performance; flange stiffness; operating conditions. For decades, ANSI flanges designed by the American National Standards Institute have provided the oil and gas industry with a suitable sealing technology, with great success. But as the needs of the oil and gas industry have changed, the deficiencies of ANSI flanges continue to be exposed.Cost-benefit principles, environmental protection and better health and safety assurance are what operators and contractors face in the 21st century

2. Causes of corrosion of stainless steel butterfly valve

The stainless steel butterfly valve is rusted during use. After metallographic structure analysis, dyeing test face, heat treatment test face, SEM and other test analysis, it is found that the key factor of material corrosion is that the carbide along the grain boundary in the material is precipitated to form a chromium-poor zone, which causes stainless steel butterfly valve corrosion. The stainless steel butterfly valve made of CF8M is rusted during use. After normal heat treatment of austenitic stainless steel, the structure should be austenite at room temperature, and the corrosion resistance is very good. In order to analyze the cause of corrosion of the butterfly valve, samples were taken on it for analysis.

Pneumatic control valve is to use compressed air as the power source, the cylinder as the actuator, and with the help of electrical valve positioner, converter, solenoid valve, retaining valve and other accessories to drive the valve, to achieve switching or proportional adjustment, receiving industrial The control signal of the automatic control system is used to adjust the flow, pressure, temperature and other process parameters of the pipeline medium. Pneumatic control valve is characterized by simple control, fast response, and intrinsic safety, without the need for additional explosion-proof measures.

Valve sealing and performance

1. The valve must be tested for performance after the final assembly

In order to check whether the product meets the design requirements and whether it meets the quality standards stipulated by the state. Defects in valve material, blanks, heat treatment, machining, and assembly can generally be exposed during testing. Conventional tests include shell strength test, sealing test, low-pressure sealing test, action test, etc., and the next test is carried out after passing the test one by one as needed.

2. Strength test

The valve can be regarded as a pressurized container, so it needs to meet the requirements of medium pressure without leakage. Therefore, the blank of the valve body, valve cover and other parts should not have defects such as cracks, loose pores, and slag inclusions that affect the strength. In addition to the strict inspection of the appearance and internal quality of the blank, the valve manufacturer should also carry out a strength test one by one to ensure the performance of the valve.

3. Butterfly valve test and installation and troubleshooting methods

Whether the butterfly valve is manual, pneumatic, hydraulic or electric, all components are strictly debugged before leaving the factory. When the user re-checks the sealing performance, they should evenly fix both sides of the inlet and outlet, close the butterfly valve, apply pressure to the inlet side, and press the inlet side. Observe whether there is leakage from the side. Before the strength test of the pipeline, the plate should be opened to prevent damage to the sealing pair.

Although the products have been strictly inspected and tested before leaving the factory, there are some products that automatically displace the screws during transportation, and need to be re-adjusted, pneumatic, hydraulic, etc., please refer to the instruction manual of the supporting drive device.

When the electric drive butterfly valve leaves the factory, the opening and closing strokes of the control mechanism have been adjusted. In order to prevent the wrong direction when the power is turned on, after the user turns on the power for the first time, first open the manual to the half-open position, and press the electric switch to check that the direction of the indicator plate is consistent with the closing direction of the valve.

4. The reason for the leakage of the pressure reducing valve

As an important component in the hydraulic system, the main function of the pressure reducing valve is to keep the outlet pressure of the system at a level lower than the inlet pressure, keep the system outlet pressure stable, and the system outlet pressure is not affected by inlet pressure and flow fluctuations ; However, once the sealing surface of the pressure reducing valve leaks, it will not only affect the normal production, but also cause the loss of hydraulic oil and pollute the environment; in the marine hydraulic system, the pressure reducing valve is the main control component, and the importance of its sealing cannot be underestimated. of. After joint research and analysis with relevant experts, it was found that the sealing between the connecting sleeve and the valve body of the pressure reducing valve mainly relies on the O-ring between the connecting sleeve and the inner wall of the valve for circumferential sealing. Leaks are inevitable.

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