Globe valves, gate valves, butterfly valves, check valves and ball valves, etc. These valves are now indispensable control components in various piping systems. Each valve is different in appearance, structure and even functional use. However, there are some similarities between the cut-off valve and the gate valve in appearance, and both have the function of cutting off in the pipeline. Therefore, there will be many friends who have little contact with the valve to confuse the two. In fact, if you look closely, the difference between the globe valve and the gate valve is quite large.
01 Structure
In the case of limited installation space selection should pay attention. The gate valve can rely on the medium pressure tightly and the sealing surface closed, so as to achieve the effect of no leakage. When the opening and closing of the valve core and valve seat sealing surface always contact and friction, so the sealing surface is easy to wear, the gate valve is close to close, the pipeline before and after the pressure difference is very large, so that the sealing surface wear is more serious.
The structure of the gate valve will be more complex than the globe valve, from the appearance point of view, the same caliber, the gate valve is higher than the globe valve, the globe valve is longer than the gate valve. In addition, the gate valve has bright and dark rod. The shutoff valve does not.
Gate Valve Structure VS Globe Valve
02 Working principle
When the cut-off valve is opened and closed, it is a rising stem type, that is to say, when the handwheel is turned, the handwheel will rotate and lift together with the stem. The gate valve is to rotate the hand wheel, so that the valve stem to do the lifting movement, the hand wheel itself position unchanged. The flow rate is different, the gate valve is required to be fully open or fully closed, and the stop valve is not required. Globe valves have specified import and export directions; gate valves have no import and export direction requirements.
In addition, the gate valve is only fully open or fully closed two states, the gate opening and closing of the stroke is very large, opening and closing time is long. The movement of the valve plate of the cut-off valve is much smaller, and the valve plate of the cut-off valve can be stopped in a certain place during the movement and used for flow regulation. And the gate valve is only do cut off use, no other function.
03 Performance differences
The cut-off valve can be used as a cut-off valve and can be used as a flow regulator. The fluid resistance of the cut-off valve is relatively large, and it is more laborious when opening and closing, but because the valve plate is short from the sealing surface, the opening and closing stroke is short.
Because the gate valve can only be fully opened and fully closed, when it is fully opened, the flow resistance of the medium in the valve body channel is almost 0, so the opening and closing of the gate valve will be very labor-saving, but the gate is far away from the sealing surface, and the opening and closing time is long.
04 INSTALLATION AND FLOW
The effect of the gate valve flowing in both directions is the same. There is no requirement for the installation of the import and export direction, and the medium can flow in both directions. The cut-off valve needs to be installed in strict accordance with the direction marked by the arrow of the valve body. There is also a clear stipulation on the import and export direction of the cut-off valve. The flow direction of the cut-off valve in our country is from top to bottom.
The cut-off valve is low and high, and it is obvious from the appearance that the pipeline is not on the horizontal line of the first phase. The flow path of the gate valve is on a horizontal line. The stroke of the gate valve is larger than that of the stop valve.
From the perspective of flow resistance, the flow resistance of the gate valve is small when it is fully open, and the flow resistance of the load valve is large. The flow resistance coefficient of ordinary gate valve is about 0.08~0.12, the opening and closing force is small, and the medium can flow in two directions. The flow resistance of ordinary stop valve is 3-5 times that of gate valve (public number: pump housekeeper). When opening and closing, forced closing is required to achieve sealing. The valve core of the globe valve is completely closed before contacting the sealing surface, so the wear of the sealing surface is very small. Due to the large flow force, the globe valve of the actuator should pay attention to the adjustment of the torque control mechanism.
There are two ways to install the stop valve. One is that the medium can enter from below the valve core. The advantage is that the packing is not under pressure when the valve is closed, which can prolong the service life of the packing and replace the packing when the pipeline in front of the valve is under pressure. The disadvantage is that the driving torque of the valve is relatively large, which is about twice that of the upper flow. The axial force of the valve stem is large and the valve stem is easy to bend. Therefore, this method is generally only applicable to small diameter valve (DN50 below),DN200 above the valve are selected from the top of the flow of media. (Electric globe valve is generally the use of media from above to enter the way.) The disadvantage of the medium entering from above is exactly the opposite of the entering from below.
Gate valve (gate valve) is an opening and closing parts of the gate, the direction of movement of the gate and the direction of the fluid perpendicular to the gate valve can only be fully open and fully closed, can not be adjusted and throttling.
Raming stem valve
Turn the hand wheel, through the hand wheel and the stem of the thread of the advance, retreat, lifting or lowering the valve plate connected with the stem, to achieve the role of opening and closing.
the advantages of bright stem gate valve:
The fluid resistance is small, and the sealing surface is washed and eroded by the medium.
Opening and closing is labor-saving.
Medium flow is not restricted, not spoiler flow, do not reduce the pressure.
The structure is simple, the structure length is short, the manufacturing process is good, and the application range is wide.
the shortcomings of the stem gate valve:
Erosion and abrasion are easily caused between the sealing surfaces, and maintenance is difficult.
The size is large, the opening needs a certain space, and the opening and closing time is long.
The structure is more complex.
Dark rod valve
Dark rod gate valve is also called rotating rod gate valve (also called dark rod wedge gate valve). The valve stem nut is located on the gate, and the hand wheel rotates to drive the valve stem to rotate, and the gate is lifted. Usually, there is a trapezoidal thread at the bottom of the valve stem. Through the thread at the bottom of the valve and the guide groove on the valve clack, the rotary motion is changed into Linear motion, that is, the operating torque is changed into operating thrust.
When the valve is opened, when the gate lift height is equal to 1:1 times the diameter of the valve, the fluid channel is completely unobstructed, but during operation, this position cannot be monitored. In actual use, the apex of the valve stem is used as a sign, that is, the position that does not move, as its fully open position. In order to consider the locking phenomenon of temperature change, it is usually opened to the top position and then returned to 1/2~1 circle as the position of the fully open valve. Therefore, the full open position of the valve, according to the position of the gate (I. e. stroke) to determine.
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 diameter or limited installation space of the gate valve. This structure is equipped with an opening and closing indicator to indicate the degree of opening and closing.
The disadvantage of this structure is that the valve stem thread not only cannot be lubricated, but also directly accepts the erosion of the medium and is easily damaged.
Bright pole VS dark pole
1. The dark rod valve cannot see the lead screw, while the bright rod can see the lead screw.
2. The lifting screw of the dark rod flange gate valve only rotates without moving up and down. What is exposed is only a rod, and its nut is fixed on the gate. The gate is lifted by the rotation of the screw, and there is no visible gantry. The lifting screw of the open rod flange gate valve is exposed, and the nut is tightly attached to the handwheel and is fixed (does not rotate or move axially). The gate is lifted by rotating the screw, the screw and the gate only have relative rotational movement without relative axial displacement, and the appearance is a gate-shaped bracket.
3. When the dark rod valve is switched, the steering wheel and the valve stem are connected together and relatively immobile. It is opened and closed by the valve stem rotating at a fixed point to drive the valve flap up and down. The open stem valve raises or lower the disc through the threaded drive between the stem and the steering wheel. To put it simply, the open stem valve is a valve disc that moves up and down together with the valve stem, and the steering wheel is always at a fixed point.