Advantage and disadvantage of various kinds of valve
- Dec 23, 2017 -

1. Gate valve: Gate valve is a valve that valve closure along the channel axis of the vertical direction of movement, mainly used in the pipeline as a cut-off medium, that is, fully open or closed. In general, the gate valve can not be used for regulating flow. It can be applied to low temperature pressure can also be applied to high temperature and pressure, according to the valve of different materials. However, gate valve is not used for transporting medium such as mud in the pipeline.

Advantages: small fluid resistance; ② open/closing required torque is small; ③ can be used in the medium flow in both directions of the ring network pipeline, which means that the flow of media is not restricted; ④ fully open, the sealing surface by the work Medium erosion than the globe valve is small; ⑤ body structure is relatively simple, manufacturing technology is better; ⑥ shorter length of the structure.

Disadvantages: ① large size and opening height, the installation space is also larger; ② in the opening and closing process, the sealing surface of the relative friction, wear larger, even at high temperatures tend to cause scratches; ③ Gate valve has two general sealing surface, giving processing, grinding and maintenance increased some difficulties; ④ open and close a long time.

 

2. Butterfly valve: Butterfly valve is a circular opening and closing pieces reciprocating about 90 ° to open, close and regulate the fluid channel of a valve.

Advantages: ① simple structure, small size, light weight, consumables province, do not use in large-caliber valves; ② quick opening and closing, flow resistance is small; ③ can be used for medium with suspended solids, according to the strength of the sealing surface can also be used Powdered and granular media. It can be used for bidirectional opening and closing and adjustment of ventilation and dust removal pipeline. It is widely used in gas pipeline and waterway of metallurgy, light industry, electricity and petrochemical industry.

Disadvantages: ① flow adjustment range is not large, when the open up to 30%, the flow will be more than 95%. ② Due to the structure of the butterfly valve and the sealing material, it is not suitable for high temperature and high pressure piping system. General operating temperature below 300, PN40 below. ③ sealing performance relative to the ball valve, globe valve is poor, it is used for sealing the place is not very high.

 

3. Ball valve: is evolved by the plug valve, and its opening and closing pieces is a sphere, the use of the ball around the axis of the stem rotated 90 ° to achieve the purpose of opening and closing. The ball valve is mainly used to cut off, distribute and change the medium flow direction in the pipeline. The ball valve designed with V-shaped opening also has good flow regulation function.

Advantages: ① has the lowest flow resistance (in fact, 0); ② due to work will not get stuck (in the absence of lubricant), it can be reliably used in corrosive media and low boiling point liquid; ③ larger Of the pressure and temperature range, can achieve a complete seal; ④ can achieve fast opening and closing, opening and closing time of some structures only 0.05 ~ 0.1s, to ensure that the test bed can be used in automation systems. Quick opening and closing the valve, the operation without impact. ⑤ spherical closure can be automatically positioned in the border position; ⑥ working medium sealed on both sides of reliable; ⑦ in the fully open and fully closed, the sealing surface of the ball and the valve seat and media isolation, so the high-speed valve through the media will not Resulting in erosion of the sealing surface; ⑧ compact structure, light weight, it can be considered for low temperature medium system is the most reasonable valve structure; ⑨ valve body symmetry, especially welded body structure, can well withstand the stress from the pipe ; ⑩ closing pieces can withstand the high pressure drop off. ⑾ fully welded ball valve body can be buried directly in the ground, so that the valve parts from erosion, the highest life of up to 30 years, is the ideal oil and gas pipelines valves.

Disadvantages: ① because the ball valve seat ring is the most important material PTFE, which is almost all of the chemical substances are inert, and has a small friction coefficient, stable performance, easy to aging, wide temperature range and sealing Excellent performance of the comprehensive features. However, the physical properties of polytetrafluoroethylene, including its high coefficient of expansion, sensitivity to cold flow and poor thermal conductivity, require that seat seal design be centered around these characteristics. Therefore, when the sealing material is hardened, the reliability of the sealing is destroyed. Moreover, the low temperature grade of PTFE, can only be used in less than 180 ℃. Above this temperature, the sealing material will age. Considering the long-term use of the case, generally only 120 ℃ do not use. ② its regulating performance relative to the cut-off valve to be worse, especially pneumatic valve (or electric valve).

 

4. Cut-off valve: refers to the closing piece (valve) moves along the valve seat center line. Depending on the type of movement of the valve disc, the change in valve seat opening is in direct proportion to the valve disc stroke. Due to the valve stem of this type of valve opening or closing stroke is relatively short, but also has a very reliable cut-off function, but also because the valve seat opening changes in proportion with the valve stroke is proportional to the flow rate is very suitable for regulation. Therefore, this type of valve is very moving together as cut off or adjust and throttle.

Advantages: ① in the process of opening and closing, due to the friction between valve disc and valve sealing surface is smaller than the gate valve, which wear. ② opening height is generally only 1/4 of the valve seat passage, so much smaller than the gate valve; ③ usually there is only one sealing surface on the valve body and valve disc, so manufacturing technology is better, easy maintenance. ④ Because of its filler is generally a mixture of asbestos and graphite, so the higher temperature grade. General steam valve with stop valve.

Disadvantages: ① due to the flow of medium through the valve has changed, so the minimum flow resistance of the globe valve is also higher than most other types of valves; ② due to longer stroke, the opening speed slower than the ball valve.

 

5. Plug valve: refers to the closure into a plunger-shaped rotary valve, through the 90 ° rotation of the valve plug on the port and the valve port on the mouth connected or disconnected, to achieve a valve on or off. The shape of the plug can be cylindrical or conical. Its principle and the ball valve is basically similar to the ball valve is developed on the basis of the plug valve, which is mainly used for oil field mining, but also for the petrochemical industry.

 

6. Diaphragm valve: refers to the valve body and bonnet with a flexible membrane or a combination of diaphragm, the closure is a diaphragm connected to a compression device. Valve acne can be weir-shaped, it can be through the wall of the runner.

Advantages: ① control mechanism separated from the media access, not only to ensure the purity of the working medium, but also to prevent pipeline medium impact on the working parts of the possibility of operating agencies, the valve stem does not require any form of separate seals, unless the control Harmful media for the use of this safety device; ② As the working medium is only contact with the diaphragm and the valve body, both can use a variety of different materials, so the valve can ideally control a variety of working media, especially for with chemical corrosion Or suspended particles. ③ simple structure, only by the valve body, diaphragm and valve cover assembly of three components. The valve is easy to disassemble and repair quickly, replacing the diaphragm can be done on site and in a short time.

Disadvantages: ① due to the valve body lining technology and diaphragm manufacturing process and the limitations of a larger valve liner and larger diaphragm manufacturing process are difficult, so the diaphragm should not be used for larger diameter, the general application of DN ≤ 200mm The following pipe. ② due to the diaphragm material restrictions, diaphragm valve for low pressure and temperature is not high occasions. Generally not more than 180 ℃; ③ adjust the performance is relatively poor, only in a small range of adjustment (usually closed to 2/3 opening, can be used for flow control).

 

7. Safety valve: refers to the pressure vessel, equipment or piping, as overpressure protection device. When the pressure in the equipment, container or pipeline exceeds the allowable value, the valve will be automatically opened and then fully discharged to prevent the equipment, container or piping and pressure from rising continuously. When the pressure drops to the specified value, the valve shall automatically Close in time to protect the safe operation of equipment, vessels or lines.

 

8. Steam traps: in the delivery of steam, compressed air and other media, there will be some condensation water formed, in order to ensure the work efficiency and safe operation of the device, it should promptly discharge these useless and harmful media to ensure that the device consumption and use. It has the following effects: ① can quickly rule out the resulting condensate; ② prevent steam leakage; ③ exclude air and other non-condensable gases.

 

9. Pressure reducing valve: through regulation, the import pressure will be reduced to a certain outlet pressure, and rely on the energy of the medium itself, so that the outlet pressure automatically maintain a stable valve.

 

10. Check valve: also known as counter-flow valve, check valve, back pressure valve and check valve. These valves are automatically opened and closed by the force generated by the flow of the medium itself in the pipeline, which belongs to an automatic valve. Check valve for piping systems, its main role is to prevent media backflow, to prevent the pump and drive motor reversal, and the release of container media. Check valves can also be used on lines where the pressure may rise above the system pressure on the auxiliary system. The main can be divided into swing-type (according to the center of gravity rotation) and the lift (along the axis of movement).