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The pipeline has become the main method of energy transportation nowadays. The pipes and valves that emerged at the right moment have developed rapidly, which has greatly promoted the process of the pipeline. How is the valve used for line pipe defined? What is the difference between their structure, characteristics and performance? Let's learn more about the distinctive valves used for pipelines.
 
The pipeline has become the main method of energy transportation nowadays, and the use of long-distance pipelines to transport oil, gas, coal, and other resources has become the most important means for energy transportation in the world today.
 
Major oil and gas producing countries and consuming countries in the world use a large number of long-distance pipelines to solve the transportation problem of oil and gas resources, and more than 95% of transportation of natural gas adopt pipelines.
1. The development history
In 1914, the first oil pipeline with a length of 9 kilometers was built in Central America, which was the beginning of the development of the pipeline industry. The cost of using pipelines to transport liquids or gases is one third of railway transportation and two third of maritime transportation, so it has achieved rapid development in the past 100 years.
 
The valves used for long-distance pipelines are 
ball valves, gate valves, check valves, and plug valves, which meet the special requirements for pipeline transportation and have special functions.
 
2. Structure and characteristics of valves used for pipelines 
Slab gate valves
Structure of slab gate valves

The slab gate valve is a sliding valve whose closing member is a parallel wedge. The closing part can be a single wedge or a double wedge with a spreading mechanism in between. The pressing force of the wedge to the valve seat is controlled by the medium pressure acting on the floating wedge or floating valve seat. If it is a double wedge slab gate valve, the expansion mechanism between the two wedges can supplement this pressing force.
 
Features of slab gate valves
Slab gate valves have features of short structure length, good sealing performance, small operating torque, close opening and closing operating force, small flow resistance, and they don't need to be equipped with abnormal pressure boosting devices. The slab gate valve with diversion holes can be cleaned by the cleaner. The structure of the slab gate valve is high, about 3 to 4 times the diameter of the pipe.
 
Ball valves
Structures of ball valves

Ball valves refer to valves that use a sphere with a circular through hole as an opening and closing part, and the sphere rotates with the valve stem to realize the opening and closing. The opening and closing part (the sphere) is driven by the valve stem and rotates around the axis of the ball valve.
 
Features of ball valves
Ball valves have the main features of compact structure, good sealing performance, quick opening and closing at an angle of 90°, short operation time. Injecting sealing grease can form a secondary auxiliary seal, and the valve seat of the fireproof structure can ensure the sealing of the valve when there is a fire. The quick cut-off device can realize the emergency opening and closing of the valve.
 
Spherical regulating valves
Structure of spherical regulating valves

The spherical regulating valve is composed of a left valve body, a valve seat, a ball, a stem shaft, and a right valve seat. It is characterized by a circular hole passage through the center of the sphere being perpendicular to the original flow passage hole. A disc is placed in the channel; the bead at one end of the disc is matched with the groove at one end of the valve stem shaft, and the other end is restricted by a limit ring.
 
Features of spherical regulating valves
The spherical regulating valve has great flow, simple structure, good stability, convenient operation and maintenance, small flow resistance at the fully opened state, great allowable pressure difference, low noise, and good cavitation resistance.
 
Check valves
Structure of check valves

The check valve has an opening pressure. When the pressure of the working medium is greater than the opening pressure of the check valve, the spring is compressed and the check valve's plate is pushed; the medium flows smoothly. When the working medium flows backwards, the medium will press the plate on the body of the check valve. The higher the pressure of the medium is, the tighter the valve body will be pressed by the plate. At this time, the plate completely separates the entire system and eliminates the possibility of the medium flowing backwards. You can visually understand the operation of check valves by the structure of the valve.
 
Feature of check valves
The 
check valve has multiple damping structures, which can effectively eliminate pipeline vibration and reduce flow resistance. It adopts double seals, that is elastic seals for low pressure, and metal to metal seals for high pressure, which has a good sealing effect. A cleaner can be used.
 
Pressure relief valves
Structure of pressure relief valves

There are two main types of pressure relief valves: the spring type and lever type. The spring type means that the sealing between the valve disc and valve seat relies on the acting force of the spring. The lever type relies on the acting force of the lever and heavy hammer. There is another impulse type pressure relief valve that is also called the pilot type pressure relief valve based on the need for large capacity, which consists of a main pressure relief valve and an auxiliary valve. When the pressure of the medium in the pipeline exceeds the specified pressure value, the auxiliary valve is opened first, and the medium enters the main pressure relief valve along the conduit; the main pressure relief valve is opened to reduce the increased pressure of the medium.
 
Feature of pressure relief valves
Because the opening and closing of the pump can cause changes in flow rates and pressure fluctuation of the medium in the pipeline, resulting in shock waves. In order to eliminate the impact of shock waves, pressure relief valves are used for long-distance pipelines to reduce shock waves.
 
Pressure reducing valves
Structure of pressure reducing valves

The pressure reducing valve is a 200X type pressure reducing valve which is adjustable and whose outlet pressure can be set through the valve spring. When the water enters the valve from the inlet end, the water flows through the needle valve to the main valve control room, and the outlet pressure acts on the pilot valve through the conduit. When the outlet pressure is higher than the setting value of the pilot valve's spring, the pilot valve is closed. The control room stops draining; at this time the pressure in the main valve control room rises and closes the main valve, and the outlet pressure no longer rises. When the outlet pressure of the valve drops to the set pressure of the pilot valve's spring, the pilot valve will be opened and the control room drains downstream.
 
Feature of pressure reducing valves
A pressure reducing valve is set on the branch pipeline to keep the medium pressure at the user's inlet end. Pilot type pressure reducing valves are mostly used, which are less affected by the cleanliness of the medium, have high-pressure control accuracy, and stable performance.

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