Gate Valve: A gate valve is a valve that uses a gate (gate plate) to move vertically along the axis of the passage. It is primarily used in pipelines for isolating the medium, i.e., fully open or fully closed. Generally, gate valves are not suitable for flow regulation. They can be used for both low temperature and high temperature and pressure applications, depending on the valve material.
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However, gate valves are generally not used in pipelines that transport slurry or similar media.
Advantages:
Low fluid resistance.
Requires a smaller torque for opening and closing.
Can be used in bidirectional flow systems, allowing the medium to flow in both directions.
When fully open, the sealing surface is less prone to erosion from the working medium compared to globe valves.
Simple structure with good manufacturing process.
Compact structure length.
Disadvantages:
Larger overall dimensions and installation space required.
Relatively higher friction and wear between sealing surfaces during opening and closing, especially at high temperatures.
Gate valves typically have two sealing surfaces, which can increase difficulties in processing, grinding, and maintenance.
Longer opening and closing time.
Butterfly Valve: A butterfly valve is a valve that uses a disc-shaped closure element to rotate about 90 degrees to open, close, and regulate fluid flow.
Advantages:
Simple structure, compact size, lightweight, and low material consumption, making it suitable for large-diameter valves.
Quick opening and closing with low flow resistance.
Can handle media with suspended solid particles and can be used for powdery and granular media depending on the strength of the sealing surface.
Suitable for bidirectional opening, closing, and regulation in ventilation and dust removal pipelines. Widely used in metallurgy, light industry, power, and petrochemical systems for gas pipelines and waterways.
Disadvantages:
Limited flow regulation range; when the valve is open by 30%, the flow rate will exceed 95%.
Unsuitable for high-temperature and high-pressure pipeline systems due to limitations in structure and sealing materials. Generally, it works at temperatures below 300°C and PN40 or below.
Relatively poorer sealing performance compared to ball valves and globe valves, hence not ideal for applications with high sealing requirements.
Ball Valve: A ball valve is derived from a plug valve, and its closure element is a sphere that rotates 90 degrees around the axis of the valve stem to achieve opening and closing. A ball valve is primarily used in pipelines for shut-off, distribution, and change of flow direction. Ball valves with V-shaped openings also have good flow regulation capabilities.
Advantages:
Minimal flow resistance (practically zero).
Reliable application in corrosive media and low boiling point liquids as it does not stick during operation (without lubrication).
Achieves complete sealing within a wide range of pressure and temperature.
Fast opening and closing, with certain structures having opening/closing times as short as 0.05 to 0.1 seconds, suitable for automation systems in testing benches without impact during operation.
Automatic positioning at boundary positions with the ball closure element.
Reliable sealing on both sides of the working medium.
No erosion of sealing surfaces from high-speed media when fully open or closed.
Compact and lightweight structure, making it the most suitable valve structure for low-temperature media systems.
Symmetrical valve body, especially in welded valve body structures, can withstand stress from pipelines.
The closure element can withstand high pressure differences during closing. Fully welded ball valves can be buried underground, ensuring the internal components are not eroded, with a maximum service life of 30 years, making them ideal for oil and gas pipelines.
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Disadvantages:
The main sealing ring material of a ball valve is polytetrafluoroethylene (PTFE), which is inert to almost all chemicals and has comprehensive characteristics such as low friction coefficient, stable performance, resistance to aging, wide temperature range suitability, and excellent sealing performance.
However, the physical properties of PTFE, including its higher expansion coefficient, sensitivity to cold flow, and poor thermal conductivity, require the design of seat seals to be based on these characteristics. Therefore, when the sealing material becomes hard, the reliability of the seal is compromised.
Moreover, PTFE has a low temperature resistance rating and can only be used below 180°C. Beyond this temperature, the sealing material will age. Considering long-term use, it is generally not used above 120°C.
Its regulating performance is relatively inferior to that of a globe valve, especially pneumatic valves (or electric valves).
Globe Valve: It refers to a valve where the closure element (valve disc) moves along the center line of the seat. The variation of the seat orifice is directly proportional to the travel of the valve disc. Due to the short opening and closing travel of this type of valve and its reliable shut-off function, as well as the proportional relationship between the variation of the seat orifice and the travel of the valve disc, it is very suitable for flow regulation. Therefore, this type of valve is commonly used for shut-off, regulation, and throttling purposes.
Advantages:
During the opening and closing process, the friction force between the valve disc and the sealing surface of the valve body is smaller than that of a gate valve, making it more wear-resistant.
The opening height is generally only 1/4 of the seat channel, making it much smaller than a gate valve.
Usually, there is only one sealing surface on the valve body and the valve disc, making it easier to manufacture and repair.
It has a higher temperature resistance rating because the packing is usually a mixture of asbestos and graphite. Globe valves are commonly used for steam valves.
Disadvantages:
Due to the change in the flow direction of the medium through the valve, the minimum flow resistance of a globe valve is higher than that of most other types of valves.
Due to the longer stroke, the opening speed is slower compared to a ball valve.
Plug Valve: It refers to a rotary valve with a closure element in the form of a cylinder or cone plug. The valve plug on the plug valve is rotated 90 degrees to connect or separate the passage on the valve body, achieving the opening or closing of the valve. The shape of the valve plug can be cylindrical or conical. Its principle is similar to that of a ball valve, which was developed based on the plug valve and is mainly used in oilfield exploitation as well as petrochemical industries.
Safety Valve: It serves as an overpressure protection device on pressurized vessels, equipment, or pipelines. When the pressure inside the equipment, vessel, or pipeline exceeds the allowable value, the valve automatically opens to release the full capacity, preventing further increase in pressure. When the pressure drops to the specified value, the valve should automatically close promptly to protect the safe operation of the equipment, vessel, or pipeline.
Steam Trap: In the transportation of steam, compressed air, and other media, condensate water is formed. To ensure the efficiency and safe operation of the device, it is necessary to timely discharge these useless and harmful media to maintain the consumption and use of the device. It has the following functions: (1) It can quickly discharge condensate water that is generated. (2) It prevents steam leakage. (3) It removes.
Pressure Reducing Valve: It is a valve that reduces the inlet pressure to a desired outlet pressure through adjustment and relies on the energy of the medium itself to automatically maintain a stable outlet pressure.
Check Valve: Also known as a non-return valve, backflow preventer, back pressure valve, or one-way valve. These valves are automatically opened and closed by the force generated by the flow of the medium in the pipeline, making them a type of automatic valve. Check valves are used in pipeline systems and their main functions are to prevent medium backflow, prevent the reversal of pumps and driving motors, and release container media. Check valves can also be used on pipelines supplying auxiliary systems where the pressure may rise above the system pressure. They can be mainly categorized into rotary type (rotates based on the center of gravity) and lift type (moves along the axis).
Post time: Jun-03-2023The starting current can be reduced by closing the discharge valve.
The current will be very high when any motor starts. When the pump is started with an open discharge valve, the discharge head will have greater resistance to the pump. Therefore, the motor must give the pump a larger starting torque, which means that the motor needs to draw more current.
If the discharge valves are closed when the pump is started, it means that there is no discharge head and minimum resistance to the pump, and therefore the output current is the smallest. Although the current is greater than the normal value when the motor starts, closing the discharge valve of the centrifugal pump can avoid additional load on the pump.
The discharge valves can be opened when there is a check valve. If there is pressure on the discharge side of the centrifugal pump without a check valve when starting, the discharge valve should be closed. With a transparent plastic pipe, leakage can be easily found. It should be used with clear PVC fittings to perform well. It's good to work with clear PVC pipe manufacturer to solve problems together.
Thinking from another aspect, if there are pressures at the discharge end of the pump, it may flow back into the pump before starting. And it will cause backward rotation, which can attract more current and cause damage to the pump. Therefore, it can be prevented by closing the discharge valve of the centrifugal pump when it starts.
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