Greasing issues for ball valve and gate valve seats
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The grease injection hole of a ball valve is located inside the seal ring, whereas that of a gate valve is outside the seal ring. This is why.
Since the design of fixed ball valves features sealing in front of the valve, that is, sealing at the inlet end valve seat, the location of the grease injection hole is within the valve seat sealing surface, which allows for effective sealing of the pressure ahead of the valve. Many manufacturers of flat gate valves are unable to implement sealing at the front of the valve; instead, they use a sealing structure at the back of the valve, that is, at the outlet end. As a result, the hole for injecting grease into the valve seat is located outside the sealing surface of the valve seat. When pressure is applied, it pushes the gate toward the valve seat at the outlet end, and the grease outside the valve seat seal helps to prevent pressure from leaking out of the valve body’s interior chamber. You can imagine it for yourself.
I agree with what was said on the second floor. Additionally, flat valve models also come with seals inside
Plate gate valves can also achieve sealing in front of the valve, as their seat structure is identical to that of fixed ball valves. As for the external grease injection you mentioned, I’ve seen flat gate valves with double gates; during the opening and closing process, the valve seat becomes separated from the gate, and solid particles may enter the valve. Over time, this can affect the proper functioning of the valve. Therefore, greasing the interior helps to prevent such particles from entering.