Summary of Advantages and Disadvantages of Various Valves – Simplify Valve Selection and Layout
Advantages and Disadvantages of Various Valves
1. Gate Valve
A gate valve refers to a valve whose closing member (gate disc) moves perpendicularly to the channel axis. It is mainly installed on pipelines to cut off media, namely used under fully open or fully closed conditions. Generally, gate valves shall not be adopted for flow regulation. They can adapt to low-temperature low-pressure as well as high-temperature high-pressure working conditions depending on valve materials. Nevertheless, gate valves are generally not applied in pipelines conveying media such as slurry.
Advantages
Low fluid resistance;
Low torque required for opening and closing;
Applicable to loop pipelines where media flows in two directions, which means the flow direction of media is unrestricted;
When fully open, erosion of the sealing surface by working media is less severe than that of globe valves;
Relatively simple structure with favorable manufacturability;
Short structural length.
Disadvantages
Large overall dimension and opening height, requiring substantial installation space;
Relative friction occurs between sealing surfaces during opening and closing, leading to heavy wear, and scoring is likely to happen under high temperature;
Most gate valves are equipped with two sealing surfaces, bringing difficulties to machining, lapping and maintenance;
Long opening and closing time.
2. Butterfly Valve
A butterfly valve is a valve that opens, closes and regulates fluid passages via reciprocating rotation of approximately 90° of a disc-shaped closure member.
Advantages
Simple structure, small size, light weight and low material consumption, especially suitable for large-diameter valves;
Fast opening and closing, low flow resistance;
Can be used for media containing suspended solid particles. Subject to the strength of sealing surfaces, it is also applicable to powdery and granular media. It can realize bidirectional opening, closing and regulation for ventilation and dust removal pipelines, and is widely used in gas pipelines and water pipelines of metallurgy, light industry, power, petrochemical systems.
Disadvantages
Limited flow regulation range; when the opening reaches 30%, the flow rate exceeds 95%;
Restricted by structure and sealing materials, butterfly valves are not suitable for high-temperature and high-pressure pipeline systems. Normal operating temperature is below 300°C and nominal pressure PN40;
Sealing performance is inferior to ball valves and globe valves, so it is adopted in occasions without strict sealing requirements.
3. Ball Valve
Evolved from plug valves, a ball valve adopts a sphere as its closure member. The sphere rotates 90° around the axis of the valve stem to realize opening and closing. On pipelines, ball valves are mainly used for cutting off, distributing and changing the flow direction of media. Ball valves designed with V-shaped openings also deliver excellent flow regulation performance.
Advantages
The lowest flow resistance (nearly zero);
No jamming during operation (even without lubricant), so it can be reliably used for corrosive media and low-boiling liquids;
Complete sealing can be achieved within a wide range of pressure and temperature;
Fast opening and closing; certain structures realize opening/closing within only 0.05~0.1s, suitable for automatic systems of test benches without impact during rapid operation;
The spherical closure member can be automatically positioned at limit positions;
Reliable bidirectional sealing of working media;
Under fully open and fully closed states, the sealing surfaces of the sphere and valve seat are isolated from media, so high-speed flowing media will not erode sealing surfaces;
Compact structure and light weight, regarded as the optimal valve structure for low-temperature medium systems;
Symmetrical valve body, especially welded valve body structure, can well withstand stress from pipelines;
The closure member can withstand high pressure difference during closing. Fully welded ball valves can be directly buried underground to protect internal components from corrosion, with a maximum service life of 30 years. They are the ideal choice for oil and natural gas pipelines.
Disadvantages
PTFE (Polytetrafluoroethylene) is the primary sealing material for valve seats. It is chemically inert to almost all substances, featuring low friction coefficient, stable performance, anti-aging property, wide applicable temperature range and excellent sealing performance. However, its physical properties including high expansion coefficient, sensitivity to cold flow and poor thermal conductivity demand targeted design of valve seat seals. Once the sealing material hardens, sealing reliability will be impaired. Moreover, PTFE has limited temperature resistance and can only be used below 180°C; the sealing material will age beyond this temperature. For long-term operation, the recommended continuous working temperature is generally below 120°C.
Its regulating performance is poorer than globe valves, especially pneumatic (or motorized) ball valves.
4. Globe Valve
A globe valve refers to a valve whose closure member (disc) moves along the centerline of the valve seat. Based on this movement mode of the disc, the variation of the valve seat flow passage is proportional to the disc stroke. This type of valve requires relatively short stem travel for opening and closing and provides reliable shut-off function. Since the flow passage opening varies proportionally with disc stroke, it is highly suitable for flow regulation. Therefore, globe valves are ideal for cut-off, regulation and throttling applications.
Advantages
During opening and closing, friction between the disc and valve body sealing surface is smaller than that of gate valves, leading to better wear resistance;
The opening height is generally only 1/4 of the valve seat passage, far smaller than that of gate valves;
Usually only one sealing surface is arranged on the valve body and disc, offering favorable manufacturability and convenient maintenance;
Its packing is generally a mixture of asbestos and graphite, resulting in high temperature resistance. Globe valves are commonly adopted for steam service.
Disadvantages
The flow direction of media changes when passing through the valve, so the minimum flow resistance of globe valves is higher than most other valve types;
Long stroke leads to slower opening speed compared with ball valves.
5. Plug Valve
A plug valve is a rotary valve with a plunger-shaped closure member. Rotating 90° enables the passage opening on the plug to communicate with or separate from the passage opening on the valve body, so as to realize opening or closing. The plug can be cylindrical or conical. Its working principle is basically similar to ball valves, and ball valves are developed on the basis of plug valves. Plug valves are mainly used in oil exploitation as well as petrochemical industry.
6. Safety Valve
A safety valve serves as an overpressure protection device installed on pressure vessels, equipment or pipelines. When the pressure inside equipment, vessels or pipelines rises beyond the allowable value, the valve opens automatically and discharges media fully to prevent continuous pressure buildup. When the pressure drops to the specified value, the valve closes automatically and timely to guarantee safe operation of equipment, vessels and pipelines.
7. Steam Trap
Condensate will form during transportation of media such as steam and compressed air. To guarantee operating efficiency and safe operation of equipment, such useless and harmful condensate must be discharged timely. Its functions are as follows:
Rapidly discharge generated condensate;
Prevent steam leakage;
Vent air and other non-condensable gases.
8. Pressure Reducing Valve
A pressure reducing valve adjusts inlet pressure down to a required outlet pressure, and automatically maintains stable outlet pressure relying on the energy of media itself.
9. Check Valve
Also known as reflux valve, non-return valve, back-pressure valve or one-way valve. As automatic valves, they open and close automatically driven by the force generated by medium flow inside pipelines. Installed in pipeline systems, check valves are mainly used to prevent medium backflow, reverse rotation of pumps and driving motors, and medium discharge from vessels. Check valves can also be installed on supply pipelines of auxiliary systems where pressure may exceed system pressure. They are mainly classified into swing type (rotating around the center of gravity) and lift type (moving along the axis).
1. Gate Valve
A gate valve refers to a valve whose closing member (gate disc) moves perpendicularly to the channel axis. It is mainly installed on pipelines to cut off media, namely used under fully open or fully closed conditions. Generally, gate valves shall not be adopted for flow regulation. They can adapt to low-temperature low-pressure as well as high-temperature high-pressure working conditions depending on valve materials. Nevertheless, gate valves are generally not applied in pipelines conveying media such as slurry.
Advantages
Low fluid resistance;
Low torque required for opening and closing;
Applicable to loop pipelines where media flows in two directions, which means the flow direction of media is unrestricted;
When fully open, erosion of the sealing surface by working media is less severe than that of globe valves;
Relatively simple structure with favorable manufacturability;
Short structural length.
Disadvantages
Large overall dimension and opening height, requiring substantial installation space;
Relative friction occurs between sealing surfaces during opening and closing, leading to heavy wear, and scoring is likely to happen under high temperature;
Most gate valves are equipped with two sealing surfaces, bringing difficulties to machining, lapping and maintenance;
Long opening and closing time.
2. Butterfly Valve
A butterfly valve is a valve that opens, closes and regulates fluid passages via reciprocating rotation of approximately 90° of a disc-shaped closure member.
Advantages
Simple structure, small size, light weight and low material consumption, especially suitable for large-diameter valves;
Fast opening and closing, low flow resistance;
Can be used for media containing suspended solid particles. Subject to the strength of sealing surfaces, it is also applicable to powdery and granular media. It can realize bidirectional opening, closing and regulation for ventilation and dust removal pipelines, and is widely used in gas pipelines and water pipelines of metallurgy, light industry, power, petrochemical systems.
Disadvantages
Limited flow regulation range; when the opening reaches 30%, the flow rate exceeds 95%;
Restricted by structure and sealing materials, butterfly valves are not suitable for high-temperature and high-pressure pipeline systems. Normal operating temperature is below 300°C and nominal pressure PN40;
Sealing performance is inferior to ball valves and globe valves, so it is adopted in occasions without strict sealing requirements.
3. Ball Valve
Evolved from plug valves, a ball valve adopts a sphere as its closure member. The sphere rotates 90° around the axis of the valve stem to realize opening and closing. On pipelines, ball valves are mainly used for cutting off, distributing and changing the flow direction of media. Ball valves designed with V-shaped openings also deliver excellent flow regulation performance.
Advantages
The lowest flow resistance (nearly zero);
No jamming during operation (even without lubricant), so it can be reliably used for corrosive media and low-boiling liquids;
Complete sealing can be achieved within a wide range of pressure and temperature;
Fast opening and closing; certain structures realize opening/closing within only 0.05~0.1s, suitable for automatic systems of test benches without impact during rapid operation;
The spherical closure member can be automatically positioned at limit positions;
Reliable bidirectional sealing of working media;
Under fully open and fully closed states, the sealing surfaces of the sphere and valve seat are isolated from media, so high-speed flowing media will not erode sealing surfaces;
Compact structure and light weight, regarded as the optimal valve structure for low-temperature medium systems;
Symmetrical valve body, especially welded valve body structure, can well withstand stress from pipelines;
The closure member can withstand high pressure difference during closing. Fully welded ball valves can be directly buried underground to protect internal components from corrosion, with a maximum service life of 30 years. They are the ideal choice for oil and natural gas pipelines.
Disadvantages
PTFE (Polytetrafluoroethylene) is the primary sealing material for valve seats. It is chemically inert to almost all substances, featuring low friction coefficient, stable performance, anti-aging property, wide applicable temperature range and excellent sealing performance. However, its physical properties including high expansion coefficient, sensitivity to cold flow and poor thermal conductivity demand targeted design of valve seat seals. Once the sealing material hardens, sealing reliability will be impaired. Moreover, PTFE has limited temperature resistance and can only be used below 180°C; the sealing material will age beyond this temperature. For long-term operation, the recommended continuous working temperature is generally below 120°C.
Its regulating performance is poorer than globe valves, especially pneumatic (or motorized) ball valves.
4. Globe Valve
A globe valve refers to a valve whose closure member (disc) moves along the centerline of the valve seat. Based on this movement mode of the disc, the variation of the valve seat flow passage is proportional to the disc stroke. This type of valve requires relatively short stem travel for opening and closing and provides reliable shut-off function. Since the flow passage opening varies proportionally with disc stroke, it is highly suitable for flow regulation. Therefore, globe valves are ideal for cut-off, regulation and throttling applications.
Advantages
During opening and closing, friction between the disc and valve body sealing surface is smaller than that of gate valves, leading to better wear resistance;
The opening height is generally only 1/4 of the valve seat passage, far smaller than that of gate valves;
Usually only one sealing surface is arranged on the valve body and disc, offering favorable manufacturability and convenient maintenance;
Its packing is generally a mixture of asbestos and graphite, resulting in high temperature resistance. Globe valves are commonly adopted for steam service.
Disadvantages
The flow direction of media changes when passing through the valve, so the minimum flow resistance of globe valves is higher than most other valve types;
Long stroke leads to slower opening speed compared with ball valves.
5. Plug Valve
A plug valve is a rotary valve with a plunger-shaped closure member. Rotating 90° enables the passage opening on the plug to communicate with or separate from the passage opening on the valve body, so as to realize opening or closing. The plug can be cylindrical or conical. Its working principle is basically similar to ball valves, and ball valves are developed on the basis of plug valves. Plug valves are mainly used in oil exploitation as well as petrochemical industry.
6. Safety Valve
A safety valve serves as an overpressure protection device installed on pressure vessels, equipment or pipelines. When the pressure inside equipment, vessels or pipelines rises beyond the allowable value, the valve opens automatically and discharges media fully to prevent continuous pressure buildup. When the pressure drops to the specified value, the valve closes automatically and timely to guarantee safe operation of equipment, vessels and pipelines.
7. Steam Trap
Condensate will form during transportation of media such as steam and compressed air. To guarantee operating efficiency and safe operation of equipment, such useless and harmful condensate must be discharged timely. Its functions are as follows:
Rapidly discharge generated condensate;
Prevent steam leakage;
Vent air and other non-condensable gases.
8. Pressure Reducing Valve
A pressure reducing valve adjusts inlet pressure down to a required outlet pressure, and automatically maintains stable outlet pressure relying on the energy of media itself.
9. Check Valve
Also known as reflux valve, non-return valve, back-pressure valve or one-way valve. As automatic valves, they open and close automatically driven by the force generated by medium flow inside pipelines. Installed in pipeline systems, check valves are mainly used to prevent medium backflow, reverse rotation of pumps and driving motors, and medium discharge from vessels. Check valves can also be installed on supply pipelines of auxiliary systems where pressure may exceed system pressure. They are mainly classified into swing type (rotating around the center of gravity) and lift type (moving along the axis).
