What are the methods for testing the sealing performance of control valve castings

As an important means of testing the sealing performance of control valve castings, water pressure test is widely used in valve quality control and verification. The operation process of this method is relatively simple and low-cost. Usually, the valve is closed, one end is connected to the test water source, and the other end is sealed. The pressure is gradually increased to the specified test pressure, which is usually 1.5 times or higher than the nominal pressure of the valve, and this pressure is maintained for 15 to 30 minutes. During this process, technicians need to carefully observe whether there is leakage in various parts of the valve, such as whether there is water droplets seeping out of the surface of the valve body, whether there is water dripping on the valve stem, etc. If the pressure does not drop significantly after the test and there is no sign of leakage, it can be determined that the sealing performance of the valve is good. However, the test pressure must be carefully controlled during the water pressure test to avoid potential damage to the valve.

Air pressure test is another commonly used sealing performance test method, which is particularly suitable for valves that are not suitable for water pressure test or application scenarios with extremely strict leakage requirements. This method is to place the valve in a sealed test container, fill it with a certain pressure of gas (such as nitrogen), and use soapy water or professional leak detection equipment to check the sealing part of the valve. If no bubbles are observed or the detection equipment shows no leakage, it indicates that the valve sealing performance is good. The advantages of air pressure test are that it has high detection sensitivity, no corrosion to the device and the working environment is kept clean, but because it involves gas pressure, the safety requirements are high and strict explosion-proof measures need to be implemented.

As a high-precision leak detection method, helium mass spectrometer leak detector detection is particularly suitable for high vacuum systems and nuclear industries that are sensitive to tiny leaks. This method uses the high permeability of helium and the high sensitivity of helium mass spectrometer leak detector for high-precision leak detection. The detection process first injects helium into one side of the valve to be tested, and then uses a helium mass spectrometer leak detector to scan and detect on the other side. When there is a leak in the valve, helium will penetrate through the leak point to the other side, and the helium mass spectrometer leak detector will capture and analyze these gases to determine the location and extent of the leak. The advantages of helium mass spectrometer leak detector are that it has high detection accuracy, accurate positioning and fast response speed, but its equipment cost is relatively high.

Ultrasonic detection technology is also an effective means to evaluate the sealing performance of control valve castings. This method relies on the propagation characteristics of ultrasonic waves in the medium to detect whether there is a leak inside the valve. During operation, place the ultrasonic probe on the sealing part of the valve to emit ultrasonic signals. When there is a leak in the valve, the ultrasonic signal at the leak point will change, such as reflection, scattering, etc. These signals will be captured and analyzed by the ultrasonic detection equipment to locate the specific location and extent of the leak. The advantages of ultrasonic detection are its non-contact, non-destructive and fast detection speed, but it requires high skills of the detection personnel.