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Gate valve according to the structure of the valve stem can be divided into: 1 Ming rod gate valve: stem nut in the valve cover or bracket, opening and closing the gate, the use of rotating stem nut to achieve stem lifting. This structure is beneficial to the lubrication of the valve stem, opening and closing a clear degree, it is widely used. 2 dark bar gate valve: stem nut in the valve body, and the media in direct contact. Open and close the gate, the rotary valve stem to achieve. The advantage of this structure is that the height of the gate valve always remains unchanged, so the installation space is small, suitable for large-caliber or gate valves with limited installation space. This structure should be equipped with an opening and closing indicator to indicate the degree of opening and closing. The disadvantage of this structure is that not only is the stem thread unlubricated, but it is also subject to direct media erosion and damage. The main difference: 1. Dark rod flange valve lifting screw is only rotating without moving up and down, exposing only a rod, the nut is fixed on the gate, through the screw rotation to improve the gate, there is no visible Of the gate; flange rod valve lifting rod is exposed, the nut close to the hand wheel and is fixed (no rotation nor axial movement), by rotating the screw to lift the gate, screw and gate only relative Rotation without relative axial displacement, the appearance of a gantry. 2 dark rod valve can not see the screw, and the rod is able to see the screw rod. 3. Dark rod valve in the steering wheel and the stem is connected together relatively immobile, it is through the valve stem at a fixed point to move the valve to promote upward and gate to complete the opening and closing. Ming rod valve is through the stem and steering wheel thread drive to raise or lower the valve. The simple point is to say that the valve rod is the valve stem together up and down movement, the steering wheel is always at a fixed point.