Internal leakage of the gate valve

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This post was last edited by Sammy_Wang on 2015-7-23 at 14:38. I mainly deal in valve business. A recent customer’s gate valve was experiencing internal leakage, but it wasn’t severe. I went to the site, removed the gate valve, and found numerous scratches on the cemented carbide; however, they weren’t very deep. In one area, the cemented carbide had been compressed resulting in a dent. Later, I found that there was a lot of welding slag inside the gate valve, both large and small pieces; among them was also a very large piece that resembled a metal gasket, measuring 1cm*2cm*3mm. What’s worse, I found many pieces of the metal winding used in those graphite-metal gaskets, each piece being about 7cm long. I suspect that someone deliberately cut those metal strips and put them into the gate valve, so as to replace them with ones that benefited that person or their suppliers. Their explanation was that those pieces fell in during the disassembly process, but that doesn’t make sense – they wouldn’t break into separate pieces during disassembly. Moreover, the valves used gaskets of DN300 size, and the thickness of those broken pieces was clearly different from that of the gaskets meant for DN300 valves. Additionally, when I checked the gaskets they removed on site, none of them were broken. Now I’m at an impasse with the client; he has his reasons, and I have my own assessments. What I’d like to ask is whether it is this welding slag and the individual metal winding sheets that cause scratches on the cemented carbide of the gate valve, thereby leading to internal leakage? The valves I sold in the past never had any problems with internal or external leakage; please help me figure this out. By the way, I’d like to do some advertising: the valves that I mainly sell are used in power plants, the chemical industry, and the metallurgy sector. I can’t reveal the brand names here; if you’re interested, feel free to contact me