Gate Valve Sealing Performance And Service Life
Nov 6, 2017
1. Gate valve definition
Is used in the pipeline is a wide range of valves, mainly play a role in closing and cutting off the media. It is not suitable for regulating the flow of the medium, but can judge the size of the flow according to the level of the stem lift (such as the elastic seat of the fire with the opening and closing scale). Gate valve compared to other valves, the pressure, temperature, caliber and other requirements to a wider range of applications.
2. The valve structure
Gate valve according to the different internal structure can be divided into: wedge single gate type, flexible gate type, double gate plate, parallel gate type.
According to the different stem stent can be divided into: gate valve and dark bar gate valve.
3. Valve body
The structure of the valve body is determined by the connection of the valve body and the pipe, the valve body and the valve cover. For the manufacturing method, there are several kinds of casting, forging, forging, casting and tube plate welding. Forged valve body has been to the direction of large diameter development, and casting body gradually to the small caliber development. Any kind of gate valve body can be forged, but also casting, should be based on user requirements and manufacturing facilities owned by the manufacturer may be.
Gate valve body of the flow channel can be divided into full diameter and reduced diameter two. Flow path and the valve through the nominal, basically the same for the full diameter; flow through the valve nominal diameter through the small known as the reduced diameter. Shrinkage shape with uniform shrinkage and cost uniform reduction of two. The flow path is tapered, which is a non-uniform diameter, which is essentially the same diameter as the nominal diameter and then shrinks to a minimum at the valve seat.
The use of reduced diameter flow channel (whether it is tapered non-uniform shrinkage or uniform diameter reduction), the advantage of the same specifications of the valve, can reduce the size of the gate, opening and closing force and torque; drawback is increased flow resistance, pressure And energy consumption increases, so shrinkage should not be too big. For the conical diameter reduction, the ratio of the inner diameter of the seat to the nominal diameter is usually 0.8 to 0.95. Nominal diameter of less than 250mm diameter of the valve, the seat diameter is generally lower than the nominal diameter of a file; nominal diameter equal to or greater than 300mm diameter reduction valve, the seat diameter is generally lower than the nominal diameter of the second gear.
5. The movement of the gate valve
When the valve is closed, the sealing surface can only rely on the media pressure to seal, that is, relying on the media pressure to press the sealing surface of the gate to the other side of the valve seat to ensure that the sealing surface of the seal, which is self-sealing. Most of the gate valve is forced to seal, that is, when the valve is closed, to rely on external force forced to the gate pressure to the valve seat to ensure that the sealing surface of the seal.
Movement mode: gate valve with the stem with a straight line movement, also called the gate valve. Usually in the lift bar with trapezoidal thread, through the top of the valve nut and the valve body on the guide groove, the rotary motion into a linear motion, that is, the operating torque into the operating thrust. When the valve is opened, when the height of the gate is equal to 1: 1 times the diameter of the valve, the fluid channel is completely open, but this position can not be monitored during operation. The actual use of the stem is the vertex as a sign, that is, the location of the open, as its full open position. In order to consider the temperature changes appear locking phenomenon, usually in the open to the vertex position, and then back 1 / 2-1 circle, as the full valve position. Therefore, the valve fully open position, according to the position of the gate (ie stroke to determine. Some gate valve stem nut is located on the gate, the hand wheel rotation to drive the stem rotation, leaving the gate lift, this valve called Rotary lever or valve stem valve.
6. Gate valve performance advantages
1. Valve fluid resistance is small, because the gate valve body is through type, the media flow does not change direction, so compared to other valve flow resistance is small;
2. Sealing performance is better than the cut-off valve, opening and closing than the cut-off valve effort;
3. Wide range of applications, in addition to steam, oil and other media, but also for the granular solid and viscosity of the larger media, but also for venting valve and low vacuum valve to use;
4. The gate valve is a double flow valve that is not limited by the flow of the medium and is therefore suitable for piping that may change the flow direction of the medium and is also easy to install.