Opening and closing the valve is something we encounter every day in our daily life. However, people who don't know the knowledge of such a small valve will operate dangerously in order to improve the knowledge of valve use. So we must pay attention to many details in our daily life
First, for the type of valve,
"Gate valve is used as cut-off medium. When it is fully open, the whole flow is straight through, and the pressure loss of medium operation is the smallest at this time. The gate valve is generally suitable for the condition that it does not need to be opened and closed frequently and keeps the gate fully open or closed. Not suitable for use as regulation or throttling. For the medium with high speed flow, the gate can vibrate when the gate is partially opened, and the vibration may damage the sealing surface of the gate and the valve seat, and the throttle will cause the gate to suffer the erosion of the medium. From the structural form, the main difference is the form of sealing elements used. According to the form of sealing elements, gate valves are often divided into several different types, such as wedge gate valve, parallel gate valve, parallel double gate valve, wedge double gate valve, etc. The most commonly used forms are wedge gate valve and parallel gate valve. "
The axis of the stop valve stem is perpendicular to the sealing surface of the valve seat. The valve stem has a relatively short opening or closing stroke and a very reliable cut-off action, which makes the valve very suitable for medium cut-off, adjustment and throttling. Once the disc of the stop valve is in the open state, there will be no contact between its seat and the sealing surface of the disc, and it has a very reliable cut-off action, so the valve is very suitable for medium cut-off, regulation and throttling.
Once the stop valve is in the open state, there will be no contact between the valve seat and the sealing surface of the disc, so the mechanical wear of the sealing surface is small. Because most of the stop valve seats and discs are easy to repair or replace the sealing elements, it is not necessary to remove the whole valve from the pipeline, which is very suitable for the occasions where the valve and the pipeline are welded together. The flow direction of medium passing through such valves has changed, so the flow resistance of stop valve is higher than that of other valves.
The commonly used stop valves are as follows: 1) angle stop valve; in the angle stop valve, the fluid only needs to change the direction once, so that the pressure drop through the valve is smaller than that of the conventional structure stop valve. 2) Direct current stop valve: in direct current or Y-shaped stop valve, the flow path of the valve body is inclined to the main flow path, so that the damage degree of the flow state is smaller than that of the conventional stop valve, so the pressure loss through the valve is correspondingly smaller. 3) Plunger type stop valve: this type of stop valve is a variation of conventional stop valve. In this valve, disc and seat are usually designed based on the principle of plunger. The valve disc is polished into a plunger plug and connected with the valve stem. The sealing is realized by two elastic sealing rings sleeved on the plunger. Two elastic sealing rings are separated by a lantern ring, and the sealing ring around the plunger is firmly pressed by the load applied on the bonnet by the bonnet nut. The elastic seal ring can be replaced and can be made of various materials. The valve is mainly used for "opening" or "closing", but it is equipped with a special plunger or a special collar, which can also be used for regulating the flow. butterfly valve
The butterfly plate of the butterfly valve is installed in the diameter direction of the pipeline. In the cylindrical channel of the butterfly valve body, the disc-shaped butterfly plate rotates around the axis, with the rotation angle between 0 ° and 90 °. When it rotates to 90 °, the valve will be fully open.
Butterfly valve is simple in structure, small in volume and light in weight, and only consists of a few parts. Moreover, the valve can be opened and closed quickly with only 90 ° rotation, and the operation is simple. At the same time, the valve has good fluid control characteristics. When the butterfly valve is in the fully open position, the butterfly plate thickness is the resistance when the medium flows through the valve body, so the pressure drop generated through the valve is very small, so it has better flow control characteristics. Butterfly valve has two types of seal: elastic seal and metal seal. Elastic sealing valve, sealing ring can be inlaid on the valve body or attached to the periphery of butterfly plate.
The service life of the valve with metal seal is generally longer than that of the valve with elastic seal, but it is difficult to achieve complete seal. The metal seal can adapt to the higher working temperature, while the elastic seal has the limitation of temperature.
If butterfly valve is required to be used as flow control, the main thing is to correctly select the size and type of valve. The structure and principle of butterfly valve is especially suitable for making large diameter valve. Butterfly valve is not only used in petroleum, gas, chemical industry, water treatment and other general industries, but also in the cooling water system of thermal power station.
There are two kinds of butterfly valves commonly used: wafer butterfly valve and flange butterfly valve. The double clip butterfly valve is connected between two pipe flanges with stud bolts. The flange butterfly valve has flange on the valve, and the flange on both ends of the valve is connected to the pipe flange with bolts.