The valves have many types. Its structure, material, driving mode and the connection are all different. It is widely used in the daily industrial and agricultural production activity and people’s daily life. As the control element of the fluid pipeline, its main function is to isolate the equipment and the pipe system, regulate the flow, prevent the backflow and adjust the pressure. Its basic function is to change the flow direction and media flow in the pipeline. Thus it can guarantee the safe operation and the smooth connection or cutting down of media circulation in the pipeline.
1.The main technical properties of the valve
A. Rigidity Property
The rigidity property of the valve refers to the ability of valve to bear the stress from media. The valve is the mechanical product to bear the inner pressure. Thus it should possess enough stiffness and strength to guarantee the long time service without breaking and deformation.
B. Sealing Property
The sealing property of valve
refers to the ability of all parts of valve to prevent the leakage of media. It is the most important technical performance index of valve. Following are three sealing place of valve:
1) The contacting place between disc and valve seat.
2) The cooperating place of padding and valve rod and stuffing box
3) The connection of valve body and valve deck
The first leakage is called inner leakage, which is not shut tightly. It will affect the ability of the valve to cut off the truncating media. For the block valve
, the inner leakage is forbidden. The latter two types are called outer leakage, which means the media is outflow from inside to the outside of the valve. The outside leakage will cause the lose of the material and pollute the surrounding. Further more it will cause accident. For the flammable and combustible, toxic or radioactive media, the outsider leakage are even not permitted. Thus the valve should have reliable sealing property.
When we choose valve, we should emphasize on the sealing performance of valve. During the operation, the sealing surface should not be suffered from any erosion. The abrasion should be very little and endurable. The advantageous sealing property may realize the zero leakage, energy saving, environment protection and high working efficiency from the inner to outer of valve sealing.
C. the flowing media
The pressure loss will be caused through media flows over the valve(it is the pressure difference around valve), which means the valve has some resistance for the valve flowing. The media in order to overcome the resistance from the valve need to consume some energy. Taking the energy saving into consideration, try to reduce the valve resistance as much as possible.
D. hoisting capacity and open and close torque
The hoisting capacity and the open and close torque are referred to the force and torque which is used to open or close the valve. When close the valve, we need to produce a certain sealing specific pressure between the two sealing surface: hoisting capacity and valve seat. And at the same time it should overcome the abrasion between valve rod and the stuffing, valve rod and the thread of the nut, of the supporting of the telos of the valve rod and other part. Thus some definite close power and close torque should be added. During the open and close of the valve process, the required hoisting capacity and open and close torque are changable. The maximum value is on the final instant of the shutting down or on the initial instant of the opening. The valve should be lowered its stopping force and stopping torque.
E. The opening and closing speed
The start and stop speed refers to the time to finish the open or close of the valve for one time. Usually there are no strict requests for the open and close of the valve. But some working condition has special request to it. For example, some requires rapid open and close to prevent the accident. Some require to close down slowly to prevent water attack. When choosing valves, please take these into consideration.
F. The flexibility and reliability of action
This refers to the sensitivity of the reaction of the valve to the media index variation. For the valve used for regulating the media index such as the throttle valve, reducing valve, regulating valve and so on, and the valve
such as the safe valve and the drain valve and other special functional valve, the flexibility and the reliability are the very important technical performance index.
G. Service life
It indicates valve durability. It is the important performance index of the valve and has very great economic meaning. Usually it is shown by the open or close times of the valve ensuring the sealing request. It also can be shown by the using time.
2. Direction and Position
Many valves has direction, such as stop valve, throttle valve, reducing valve, check valve and so on. If you install conversely, then the using effect and the shelf life will be influenced like throttle valve, or it doesn’t work like reducing valve, or even cause the danger like check valve). For the usual valve there are directional signal on the body. If not, please distinguish according to the working principle of the valve. The stop valve pocket is asymmetry in the left and right. The fluid will flow from the down to the up through the valve mouth and this makes the fluid resistance small(decided by the shape). The stop valve saves power when open it and the media won’t press the stuffing when it closes. This is convenient for repairing. This is why the stop valve can not equip conversely. The other kind of the valves should have their own characteristic. The installing position of the valve should be convenient for operation. Even though The installation is difficult, the operator’s long time working should be considered.
3. The installation and construction
Installation should be careful. Do not hit on the valve made of the fragile material.
Before installation, check the valve first, inspect on the specification, if being damaged or not, especially for the valve rod, turning several times to see if it is oblique because during transportation the rod is the most easily damaged thing. Get rid of the sundries in the valve. When lift the valve, do not tie the rope on the hand wheel or valve rod so as not to hurt these parts. The rope should be tied on the flange. All the pipelines which the valve connects should be cleaned well. Use the air compressing way to eliminate the iron oxide, mud, welding slag and other sundries. These things not only easily scratch on the sealing surface, but also the big particle among it (such as welding slag) can block the small valve and make it invalid. When equipping the nut valve, please stuff the sealing(Chinese grass with lead oil or teflon raw material). Pack on the pipe thread. Do not put it in the valve so as to avoid inner storage and affect the media circulation.
Some valves need the outer protection which is heat prevention and coldness insulation. In the insulating layer it needs the heating steam pipeline. What kind valve need to be insulated? It is according to the production request. In principle, if the media temperature in the valve reduce too much, the valve will be broken and the production efficiency will be lower. Thus it needs to be insulated or heat tracing. If the valve is exposed, it will do harms to the production or cause frosting and so on, so it needs coldness insulation. The heating preventing material includes: asbestos, slag cotton, glass cotton, perlite, diatomite, vermiculite. The coldness insulating material includes: soft wood, perlite, foam, plastic and so on. The water or steam, do not use for a long time, should be given up.
For the storing valve
, some stuffing are out of use, some are not fit for the media. It is necessary to replace those stuff. The valve factory can not take all the thousands of the media into consideration. The stuffing box should always be put in the common packing. But when using it, the packing should be fit for the media. When replacing the stuffing, press the stuff into the box one lap by one lap. The joint seam of each lap should be 45 degree. The joint seam between laps should be departed with 180 degree. The stuffing height should consider the leeway for the cover to compact. And also make stuffing box proper deep. The depth is usually 10-20% of the total depth of the stuffing box.
For the high request valve, the joint seam angle should be 30 degree. The joint seam between the laps should be divided by 120 degree. Besides the above stuffing place, we can use the following stuffing according to the actual situation: rubber O ring (the natural rubber can resist the weak base below 60 degree, the nitrile rubber resists oil below 80 degree, the fluororubber resists the multiple corrosive media under 150 degree), the three fold type teflon ring(resists strong corrosive media below 200 degree), the nylon bowl ring(resists the ammonia, alkali below 120 degree) and so on.