Structure of Elastic Seat Sealed Gate Valves
1. The Sealing Structure of the Valve Stem
The valve stem seal adopts three O-ring knots. The third O-ring can reduce the pressure at the gland and also enable the replacement of the upper two sealing rings in the pipeline under medium pressure (replacing the valve stem seal and packing under pressure is very dangerous, so this practice is not recommended). Compared with using a stuffing box, the O-ring sealing structure can effectively reduce the opening and closing torque of the valve. The O-ring sealing structure requires higher machining accuracy and surface roughness accuracy of the valve stem than those of the packing structure, otherwise, it may cause the cutting of the O-ring.
2. The Structure of the Wedge
There are mainly two types of gate seals: cut-off and wedge. The cut-off type is commonly used in specifications above DN250, with the characteristic that the side rubber does not play a sealing role. In the closing process, the rubber on the side of the wedge does not compress and deform with the inner wall of the valve body, and only seals when the rubber deforms during the final closing. The wedge type is commonly used in sizes below DN250, characterized by the sealing effect of the side rubber. In the closing process, the inner wall of the rubber valve body on the side of the wedge is squeezed and deformed, forming a sealing surface. In the opening and closing process, the torque is greater than that of valves with the same type and specification, and the casting requirements for the valve body are relatively less. There is no significant difference between the two structures in use.
3. Common Valve Stem Nut Connection Forms
The connection between the wedge and the valve stem nut of the elastic seat sealed gate valve has two structures: T-nut type and integral embedded type. The T-shaped nut type structure is simple, and there is an adjustment gap between the nut and the gate, which can simplify the manufacturing process of the gate and reduce requirements. However, long-term use may cause the T-shaped nut to wear the rubber layer of the gate, exposing the iron core and causing rust. The overall embedded structure is complex, with no adjustment gap between the nut and the wedge. The manufacturing process of the gate is complex, and high precision requirements are required for the processing and assembly of various parts. However, the structure is reliable and there will be no rubber layer wear.
Whether it is a rising stem or a non-rising stem elastic seat sealed gate valve, the gate is subjected to the static pressure of the medium in the sealing process. The gate moves towards the direction of medium flow due to the presence of assembly gaps between valve stems and other parts, further compressing the outlet sealing surface. At the same time, the compression of the imported wedge surface is also reduced by an equal amount, weakening or even losing the sealing conditions, forming a mandatory sealing of the unilateral wedge surface.
The valve stem seal adopts three O-ring knots. The third O-ring can reduce the pressure at the gland and also enable the replacement of the upper two sealing rings in the pipeline under medium pressure (replacing the valve stem seal and packing under pressure is very dangerous, so this practice is not recommended). Compared with using a stuffing box, the O-ring sealing structure can effectively reduce the opening and closing torque of the valve. The O-ring sealing structure requires higher machining accuracy and surface roughness accuracy of the valve stem than those of the packing structure, otherwise, it may cause the cutting of the O-ring.
2. The Structure of the Wedge
There are mainly two types of gate seals: cut-off and wedge. The cut-off type is commonly used in specifications above DN250, with the characteristic that the side rubber does not play a sealing role. In the closing process, the rubber on the side of the wedge does not compress and deform with the inner wall of the valve body, and only seals when the rubber deforms during the final closing. The wedge type is commonly used in sizes below DN250, characterized by the sealing effect of the side rubber. In the closing process, the inner wall of the rubber valve body on the side of the wedge is squeezed and deformed, forming a sealing surface. In the opening and closing process, the torque is greater than that of valves with the same type and specification, and the casting requirements for the valve body are relatively less. There is no significant difference between the two structures in use.
3. Common Valve Stem Nut Connection Forms
The connection between the wedge and the valve stem nut of the elastic seat sealed gate valve has two structures: T-nut type and integral embedded type. The T-shaped nut type structure is simple, and there is an adjustment gap between the nut and the gate, which can simplify the manufacturing process of the gate and reduce requirements. However, long-term use may cause the T-shaped nut to wear the rubber layer of the gate, exposing the iron core and causing rust. The overall embedded structure is complex, with no adjustment gap between the nut and the wedge. The manufacturing process of the gate is complex, and high precision requirements are required for the processing and assembly of various parts. However, the structure is reliable and there will be no rubber layer wear.
Whether it is a rising stem or a non-rising stem elastic seat sealed gate valve, the gate is subjected to the static pressure of the medium in the sealing process. The gate moves towards the direction of medium flow due to the presence of assembly gaps between valve stems and other parts, further compressing the outlet sealing surface. At the same time, the compression of the imported wedge surface is also reduced by an equal amount, weakening or even losing the sealing conditions, forming a mandatory sealing of the unilateral wedge surface.
