Valve air pressure

In valve testing, \"forward testing\" and \"reverse testing\" refer to the methods or directions of pneumatic testing for valves, with the aim of checking whether the valve’s sealing performance meets the required standards. The main difference between the two testing methods lies in the way and sequence in which the medium (air in this case) is applied under pressure to the valve, as well as the direction of the pressure acting inside the valve body. Below are the specific explanations and differences between these two methods. 1. Direct testing: This method is carried out with the valve in a partially open or fully open position. First, inject gas or liquid at a certain pressure into the valve, then slowly close the valve. The key point of the test is that, during the closing process, the internal medium exerts pressure on the valve seat and sealing surfaces; thereafter, it is checked whether there are any leaks on the outside of the valve once it is fully closed. If there is severe leakage during the closing process, it indicates that the valve does not provide an adequate seal when in contact with the sealing surface. 2. Reverse test: The reverse test is carried out with the valve fully closed. After the valve is fully closed, water or another fluid should be poured into it to ensure that the sealing surfaces are covered by the liquid, and only then should a pressure test be conducted on the valve. The advantage of this approach is that when the valve is closed, the sealing surface is already tightly enclosed by the medium; as a result, it is easier to detect minor leaks when pressure is applied later. In your description, the first scenario is \"direct operation\"; since the valve is not completely closed when pressure is applied, the sealing surfaces may not make full contact, or there may be issues with the valve’s sealing performance itself, which results in severe air leakage. The second scenario is \"counter-pressure testing\"; since the valve is fully closed and the sealing surface is in tight contact with the valve seat, applying pressure at this point tests the sealing quality after closure, so basically no leakage occurs. In actual valve testing, different testing methods are selected based on various standards and the type of valve, in order to ensure the reliability and sealing performance of the valves in real-world use. These two different testing methods can help identify potential issues with valves under various operating conditions. .

The pressure testing method should be determined based on the type and structure of the valve

Valves come in various structures, and it is best to conduct pressure testing based on the principles of those valve structures. The common method for pressure testing valves involves pressurizing them while they are closed, in the direction of fluid flow, and using a foaming technique to check the sealing condition between the valve core and the valve seat. Use a blind flange on the outlet side of the valve and open it fully to test for leaks in the packing at the valve stem. This requires a leak test with the packing seal tightened. Because during use, in order to easily operate the valves, some people loosen the packing compression bolts and tighten them again after operation. This requires a normal fluid; this method cannot be used if the fluid is toxic or harmful. Regardless of the name given to it, pressure testing based on the principle of operation is the most appropriate approach. Based on this pressure testing method you mentioned, I’m not sure what the results will be. For reference. The master’s words aren’t always absolutely correct; they can serve as a reference, but it’s still necessary to follow the principles.

So, is this related to the operating conditions or to the valve structure? These are globe valves