Valve is the valve down part (disc) moving along the vertical direction of the channel centerline. Gate valve in the pipeline can only be fully open and fully closed off, can not be adjusted and the throttle. The gate valve is a valve, use a wide range of general caliber DN ≥ 50mm cut-off device to have chosen it, sometimes caliber small cut-off device selection gate valve,

Gate two sealing surface, the most commonly used wedge gate valve sealing surface formed two wedge-shaped wedge angle with the valve parameters, usually 50, 52 medium temperature is not high. Wedge gate valve can be made ??into a whole, called the rigid damper; trace deformation of the gate can also be made ??to improve their craft, to make up for the sealing surface angle deviation in the process, this The gate is called the elastic damper.

Valve closed, the sealing surface can only rely on media pressure to seal, that is, the medium pressure to the sealing surface of the ram pressure to the other side of the seat to ensure the sealing surface of the seal, which is self-sealing. Most of the valve is sealed by force, the valve is closed, we have to rely on external force to the ram pressure to the valve seat to ensure that the sealing surface of the seal.

Gate valve with the valve stem with a straight-line movement, called the lift rod valve (also called clear shot valve). Usually lift rod with trapezoidal thread, the rotary motion into linear motion through the valve at the top of the nut and the guide groove on the body, that is, the operating torque thrust into action.

Open the valve, gate valve lift height equal to the valve diameter of 1:1, the fluid channel is completely smooth, but at run time, this location can not be monitored. Actual use, is the culmination of the stem as a symbol, which means that the fixed position, as its fully open position. Temperature appears to consider locking phenomenon, usually open to the vertex position, then back 1/2-1 circle, as the fully open valve position. Therefore, the valve fully open position, according to gate position (ie, travel> to determine.

The gate valve of the advantages:

Fluid resistance is small because (1) The internal media channel of the valve body is straight, the media flows through the valve does not change its flow direction, so fluid resistance.
(2) opening and closing moments, opening and closing more effort because the ram direction of movement and direction of media flow perpendicular to the gate valve, globe valve, gate valve opening and closing more effort.
(3) the direction of media flow unrestricted, non-spoiler, do not reduce the pressure medium can flow from any direction of the gate valve on both sides of the can reach the purpose of use. More suitable for the pipeline medium flow direction may change.
(4) The structure length is shorter because of the gate valve is vertically on the valve body, and closing the valve disc is level in the valve body, and thus the length of the structure is shorter than globe valves.
(5) The sealing performance of a good full sealing surface by erosion.
(6) erosion than globe valves fully open, the sealing surface of the working medium.
(7) The body is relatively simple, good casting process for a wide range.

Valve defects:

Between (1) easy to damage the sealing surface of the opening and closing the gate contact with the valve seat seal while the relative friction, easy to damage, the impact of seals and service life, maintenance more difficult.
(2) opening and closing time length, height and gate valve shall be fully open or fully closed, the ram stroke, open space to be certain, high dimensions, the larger space required for installation.
Gate valve (3) the complex structure generally have two sealing surface, to the processing, polishing and maintenance of some additional, more difficult parts, manufacturing and maintenance more difficult, the cost is higher than the cut-off valve.

Gate valve diameter contraction:
If a channel diameter of the valve body is not the same (and often are the valve seat diameter less than the flange joint diameter), known as the diameter contraction.
Diameter shrink parts sizes shrink, opening and closing force required to be reduced accordingly, at the same time expand the scope of application components. But the path contraction. Fluid resistance loss increases.
Certain conditions in certain sectors (such as the petroleum sector, oil pipelines), the diameter contraction of the valve are not allowed. This regard in order to reduce the pipeline pressure losses, on the other hand, in order to avoid the path an obstacle to the mechanical cleaning pipeline contraction.

palabras clave: Gate valves, linear motion, lift rod, valves, valve seats,