I. DEFINITION OF GATE VALVE
It is a kind of valve which is widely used in the pipeline, and mainly plays the role of connecting and truncating the medium. Not suitable for regulating the flow of media, but can be based on the height of the valve stem to determine the flow size (such as fire-fighting with the resilient seat seal valve with a hoist scale). Gate valves compared with other valves, the pressure, temperature, caliber and other requirements of the scope of application to be wide.
Two. GATE Valve structure
Gate Valve According to the internal structure of the different can be divided into: wedge-type single gate plate, elastic gate plate, double gate plate, parallel gate plate.
According to the different stem bracket can be divided into: Ming Rod gate valve and dark rod gate valve.
Three. Valve Body and runner
The structure of the gate valve body determines the connection between the valve body and the pipe, the valve body and the bonnet, and in terms of the manufacturing method, there are several kinds of casting, forging, forging welding, casting welding and tube plate welding. The forging valve body has developed to the large caliber direction, and the casting valve body gradually develops to the small caliber. Any kind of gate valve body can be forged, also can be cast, should be based on user requirements and manufacturing tools owned by the manufacturer.
Gate valve body Flow path can be divided into two types, full diameter type and shrink diameter. Flow channel aperture and valve nominal path, basically the same as the full diameter type, the circulation aperture than valve nominal flow small called shrink-diameter. The necking shape has two kinds of uniform shrink diameter and cost uniform shrink diameter. The flow path assumes the cone tube shape is one kind of non-uniform shrinkage diameter, this kind of valve inlet end aperture basically and the nominal pass diameter is same, then reduces gradually, to the seat place reduces to the smallest.
The use of shrink-type flow path (whether conical tube-shaped uneven or uniform shrinkage diameter), the advantages of the same specification of the valve, can reduce the size of the gate, the opening and closing force and torque; For tapered tubular necking, the diameter of the seat is usually 0.8 ~ 0.95. Nominal diameter less than 250mm of the reducer valve, the valve seat diameter is generally lower than the nominal diameter of one gear; nominal diameter is equal to or greater than 300mm of the reduction valve, the valve seat diameter is generally lower than the nominal diameter of two files.
Four. Gate Valve movement Mode
When the gate valve is closed, the sealing surface can only rely on the medium pressure to seal, that is to rely on the medium pressure to press the seal surface of the gate to the other side of the valve seat to ensure sealing surface, this is the self sealing. Most of the gate valves are forced seal, that is, when the valve is closed, it is necessary to force the gate to be pressed to the seat by external forces to ensure sealing of the seal surface.
Movement mode: Gate valve of the gate with the valve stem for a straight line movement, also known as the Ming rod gate valve. Usually, there is a trapezoidal thread on the lifter, through the nut on the top of the valve and the guide groove on the valve body, turning the rotation movement into a straight line motion, that is, turning the operation torque into operational thrust. When opening the valve, when the gate lifting height is equal to the valve diameter of 1:1 time times, the flow of the channel is fully unblocked, but at run time, this location is not monitored. In actual use, it is the vertex of the stem as a sign, that is, the position of the open, as its full opening position. In order to consider the phenomenon of temperature change deadlock, usually in the vertex position, and then pour back to the 1/2-1 circle, as the position of open valve. Therefore, the open position of the valve, according to the position of the gate (that is, stroke) to determine. Some gate valve stem nut is located on the brake board, the handwheel rotates to drive the stem to rotate, and make the gate ascend, this kind of valve is called the revolving rod gate valve or called the Dark Pole gate valve.
Five. Gate Valve Performance Advantages
1. The valve fluid resistance is small, because the gate valve body is the straight-through type, the medium flow does not change the direction, therefore compares other valve flow resistance to be small;
2. The sealing performance is better than the cut-off valve, and the closing valve is more labor-saving;
3. Wide range of application, in addition to steam, oil and other media, but also applicable to contain granular solids and viscosity of the medium, but also to do vent valve and low vacuum system valve to use;
4. The gate valve is a valve with double flow direction, and is not restricted by the medium flow, so it is suitable for the pipeline which the medium may change the flow orientation, but also facilitates the installation.
Six. Gate Valve performance Disadvantage
1. The shape design size is high, the closing time is long. On opening the valve plate to be elevated to the upper part of the valve, when the closure needs to be all the valve seat, so the valve plate opening and closing stroke large, long time;
2. As the valve plate and valve seat of the two sealing surface in the process of opening and closing friction, so the sealing surface easy to scrape, the sealing performance and service life have an impact, and difficult to repair.
Seven. Performance comparison of different structure gate valves
1. Wedge type single GATE gate valve
A, the structure is simpler than the elastic gate valve;
b, at a higher temperature, the sealing performance is not as good as the elastic gate valve or double gate valve;
C, suitable for easy coking high-temperature medium.
2. Flexible Gate Valve
A, it is a special form of wedge type single gate valve. Compared with the wedge-type gate valve, at high temperature, the sealing performance is good, the gate board is not easy to be jammed after heating;
b, applicable to steam, high-temperature oil and oil and gas medium, and is suitable for frequent switching parts;
c, not suitable for easy coking medium.
3. Double Gate Gate Valve
A, the sealing performance is better than the wedge-type gate valve, when the angle of the sealing surface and the valve seat match are not very accurate, still have good sealing performance;
B, the gate seal surface wear, the spherical top of the bottom of the metal pad can be replaced after the use, generally do not have to heap welding and grinding cover;
C, applicable to steam, high-temperature oil and oil and gas medium, and is suitable for frequent switch parts;
D, not suitable for easy coking medium.
4. Parallel Gate Valve
A, sealing performance is worse than other forms of gate valve;
b, suitable for the medium with low temperature and pressure;
c, gate and valve seat sealing surface processing and maintenance than other forms of gate simple.
Eight. Gate Valve installation Precautions
1. Before installation must check the valve cavity and the close cover and so on, does not permit the dirt or the sand grain to attach.
2. Each connecting part bolts, the request is evenly screwed tightly.
3. Check the filling site pressure, not only to ensure the sealing of fillers, but also to ensure the opening of the brake board flexible.
4. Before the installation of forged steel gate valve, users must proofread the valve model, connection size and attention to the media flow, to ensure consistency with the valve requirements.
5. When installing forged steel gate valves, the user must reserve the necessary space for valve actuation.
6. The wiring of the driving device shall be carried out according to the wiring diagram.
7. Forged STEEL gate valve must be maintained on a regular basis and shall not be randomly impacted and extruded to avoid affecting the seal.