Ultimate Guide of Commonly Used Valves

Considering the working principle, function, and valve structure, valves can be divided into gate valve; butterfly valve; stop valve; check valve; plug valve; ball valve; pinch valve; diaphragm valve; plunger valve, etc.

 

Gate valve

A gate valve refers to a valve whose closing part (gate) moves along the vertical direction of the channel axis. It is mainly used for cutting off the medium in the pipeline, that is, fully open or fully closed. Generally, the gate valve cannot be used for regulating flow. It can be suitable for low-temperature pressure or high temperature and high pressure, and according to different materials of the valve. However, gate valves are generally not used in pipelines that transport mud and other media.

 

Gate valve advantage

① Small fluid resistance;

② The torque required for opening and closing is small;

③ It can be used on the ring network pipeline where the medium flows in both directions, which means that the flow direction of the medium is not restricted;

④ When fully open, the erosion of the sealing surface by the working medium is smaller than that of the stop valve;

⑤ The body structure is relatively simple, and the manufacturing process is better;

⑥ The structure length is relatively short.

 

Gate valve disadvantages

① The external dimensions and opening height are large, and the space required for installation is also large;

② In the process of opening and closing, the sealing surface is relatively rubbed by people, and the abrasion is large, and it is easy to cause scratches even at high temperatures;

③ Generally, gate valves have two sealing surfaces, which adds some difficulties in processing, grinding, and maintenance;

④ Long opening and closing time.

 

Butterfly valve

A butterfly valve is a valve that uses a disc-type opening and closing member to reciprocate about 90° to open, close, and adjust the fluid channel.

 

Butterfly valve advantage

① Simple structure, small size, lightweight, saving consumables, do not use in large-diameter valves;

② Rapid opening and closing, small flow resistance;

③ It can be used for media with suspended solid particles, and it can also be used for powder and granular media depending on the strength of the sealing surface. It can be applied to the two-way opening and closing and adjustment of ventilation and dust removal pipelines and is widely used in gas pipelines and waterways in metallurgy, light industry, electric power, and petrochemical systems.  

   

Butterfly valve disadvantages

① The flow rate adjustment range is not large. When the opening reaches 30%, the flow rate will enter more than 95%.

② Due to the limitation of the structure of the butterfly valve and the sealing material, it is not suitable to be used in the high temperature and high-pressure pipeline system. The general working temperature is below 300℃ and below PN40.

③ The sealing performance is poorer than that of ball valves and globe valves, so it is used in places where the sealing requirements are not very high.

 

Ball valve

It is evolved from the plug valve. The opening and closing part is a sphere, which uses the sphere to rotate 90° around the axis of the valve stem to achieve the purpose of opening and closing. The ball valve is mainly used for cutting off, distributing, and changing the flow direction of the medium in the pipeline. The ball valve designed as a V-shaped opening also has a good flow adjustment function.      

 

Ball valve advantage

①Have the lowest flow resistance (actually 0);

②Because it will not get stuck during work (when there is no lubricant), it can be reliably used in corrosive media and low boiling point liquids;

③Complete sealing can be achieved in a larger pressure and temperature range;

④ Fast opening and closing can be realized. The opening and closing time of some structures is only 0.05~0.1s to ensure that it can be used in the automation system of the test bench. When opening and closing the valve quickly, there is no shock in operation.

⑤The spherical closure can be automatically positioned at the boundary position;

⑥The working medium is reliably sealed on both sides;

⑦When fully open and fully closed, the sealing surface of the ball and the valve seat is isolated from the medium, so the medium passing through the valve at high speed will not cause erosion of the sealing surface;

⑧Compact structure and lightweight, it can be considered as the most reasonable valve structure for the cryogenic medium system;

⑨The valve body is symmetrical, especially the welded valve body structure, which can withstand the stress from the pipeline well;

⑩The closing piece can withstand the high-pressure difference when closing.

⑪The ball valve with a fully welded body can be directly buried in the ground so that the internal parts of the valve are not corroded, and the maximum service life can reach 30 years. It is the most ideal valve for oil and natural gas pipelines.

 

Ball valve disadvantages

① Because the main seat sealing ring material of the ball valve is polytetrafluoroethylene, it is inert to almost all chemical substances and has a small friction coefficient, stable performance, not easy to age, wide temperature application range, and sealing comprehensive features with excellent performance. However, the physical properties of PTFE, including high expansion coefficient, sensitivity to cold flow, and poor thermal conductivity, require the design of valve seat seals to focus on these characteristics. Therefore, when the sealing material becomes hard, the reliability of the seal is impaired. Moreover, PTFE has a low-temperature resistance grade and can only be used at less than 180°C. Above this temperature, the sealing material will deteriorate. When considering long-term use, it will generally only be used at 120°C. 

② Its adjustment performance is worse than that of the stop valve, especially the pneumatic valve (or electric valve).

 

Shut-off valve

The shut-off valve refers to the valve whose closing part (disc) moves along the centerline of the valve seat. According to this movement of the valve disc, the change of the valve seat port is proportional to the valve disc stroke. Because the opening or closing stroke of the valve stem of this type of valve is relatively short, and it has a very reliable shut-off function, and because the change of the valve seat port is in direct proportion to the stroke of the valve disc, it is very suitable for flow adjustment. Therefore, this type of valve is very suitable for cutting off or regulating and throttling.      

 

Shut-off valve advantage

① During the opening and closing process, the friction between the disc and the sealing surface of the valve body is smaller than that of the gate valve, so it is wear-resistant.

② The opening height is generally only 1/4 of the valve seat passage, so it is much smaller than the gate valve;

③ Usually there is only one sealing surface on the valve body and disc, so the manufacturing process is better and it is easy to maintain.

④ As the filler is generally a mixture of asbestos and graphite, the temperature resistance level is higher. Generally, steam valves use stop valves.

 

Shut-off valve disadvantages

① Since the flow direction of the medium through the valve has changed, the minimum flow resistance of the stop valve is also higher than that of most other types of valves;

② Due to the longer stroke, the opening speed is slower than that of the ball valve.

 

Plug valve

A plug valve refers to a rotary valve with a plunger-shaped closing member. The passage opening on the valve plug is communicated with or separated from the passage opening on the valve body through a 90° rotation to realize opening or closing. The shape of the valve plug can be cylindrical or conical. The principle is basically similar to that of the ball valve. The ball valve is developed on the basis of the plug valve. It is mainly used for oilfield exploitation, but also for the petrochemical industry.      

 

Diaphragm valve

Diaphragm valve refers to a flexible membrane or combined diaphragm installed in the valve body and bonnet, and the closing part is a compression device connected with the diaphragm. The valve acne can be weir-shaped, or it can be a pipe wall that passes through the flow channel.

 

Diaphragm valve advantage

① The control mechanism is separated from the medium passage, which not only ensures the purity of the working medium but also prevents the possibility of the medium in the pipeline from impacting the working parts of the control mechanism. There is no need to use any form of the separate seal at the valve stem unless it is controlling harmful media Used in this safety facility;

② Because the working medium is only in contact with the diaphragm and the valve body, both of which can use a variety of different materials, the valve can ideally control a variety of working media, especially suitable for media with chemical corrosion or suspended particles.

③ Simple structure, only composed of three parts: valve body, diaphragm, and valve cover assembly. The valve is easy to quickly disassemble and repair, and the replacement of the diaphragm can be completed on-site and in a short time.      

 

Diaphragm valve disadvantages

① Due to the valve body lining process and diaphragm manufacturing process and restrictions, larger valve body lining and larger diaphragm manufacturing process are difficult, so the diaphragm is not suitable for larger pipe diameters, generally used in DN≤200mm On the pipeline.

② Due to the limitation of diaphragm material, the diaphragm valve is suitable for low pressure and low-temperature occasions. Generally does not exceed 180°C;

③ The adjustment performance is relatively poor, and it is only adjusted in a small range (usually used for flow adjustment when closed to 2/3 opening).

 

Safety valve

Safety valve refers to the pressure vessel, equipment or pipeline, as an overpressure protection device. When the pressure in the equipment, container, or pipeline rises above the allowable value, the valve will automatically open, and then the full amount will be discharged to prevent the equipment, container, or pipeline and the pressure from continuing to rise; when the pressure drops to the specified value, the valve should automatically Close in time to protect the safe operation of equipment, containers or pipelines.    

 

Steam trap

Some condensed water will be formed in the conveying of steam, compressed air, and other media. In order to ensure the working efficiency and safe operation of the device, these useless and harmful media should be discharged in time to ensure the consumption and use of the device.

It has the following functions:

① Can quickly remove the condensed water produced;

②Prevent steam leakage;

③Exclude air and other non-condensable gases.      

 

Pressure reducing valve

The pressure reducing valve is a valve that reduces the inlet pressure to a certain required outlet pressure through adjustment and relies on the energy of the medium itself to automatically maintain a stable outlet pressure.      

 

Check valve

Check valves are also known as counterflow valves, check valves, back pressure valves, and check valves. These valves are automatically opened and closed by the force generated by the flow of the medium in the pipeline, and belong to an automatic valve. The check valve is used in the piping system. Its main function is to prevent the medium from flowing back, prevent the pump and the drive motor from reversing, and to discharge the container medium. The check valve can also be used to supply the auxiliary system whose pressure may rise above the system pressure. It can be divided into swing type (rotating according to the center of gravity) and lifting type (moving along the axis).