Application of Butterfly Valves in Piping Systems: Why are they needed in combination with other valves?
In various industrial and municipal piping systems, fluids frequently need to be opened, closed, and regulated. Butterfly valves account for a significant portion of the valve market due to their simple structure, light weight, low cost, and ease of operation.
Of course, one tree cannot make a forest; the existence of other valve types is also for a reason. In engineering applications, relying solely on butterfly valves often fails to meet the system’s requirements for safety, stability, and precise control. Therefore, butterfly valves typically need to be used in conjunction with other types of valves (such as filters, pressure reducing valves, check valves, etc.) to form a complete control system.
This article will systematically analyze the collaborative use of butterfly valves in pipelines from aspects such as application principles, typical combinations, installation sequence, selection recommendations, common problems, and troubleshooting.
1. Functions and Limitations of Butterfly Valves
A butterfly valve is a valve that controls the flow of fluid by rotating a valve plate from 0 to 90 degrees. It is suitable for controlling the opening and closing of water, air, oil, and some corrosive media, as well as for coarse flow regulation and pipeline isolation.
However, as mentioned above, butterfly valves also have limitations:
– Lack of filtration capability: Butterfly valves not only lack filtration functionality but are also sensitive to the media in the fluid, especially soft-seal butterfly valves. Impurities and rust can easily damage the sealing surface and even prevent the valve from opening and closing.
– Inability to manage pressure: Butterfly valves do not have automatic pressure stabilization capabilities. If the inlet pressure fluctuates too much, it may affect downstream equipment.
– Limited fine-tuning capability: As shown in the figure below, although the flow curve of a butterfly valve approaches a percentage,
Because of these limitations, butterfly valves are usually defined as “actuating valves” in engineering, and sometimes need to rely on other functional valves to work in conjunction.
2. Common Combined Uses of Butterfly Valves
2.1. Butterfly Valve + Y-type Filter Strainer
One of the most common combinations is the use of a butterfly valve in conjunction with a Y-type filter strainer. As the name suggests, a Y-type filter is a filtration device used to remove impurities from the medium, such as large particles of mud and sand, iron filings, welding slag, and other solid particles. Therefore, filters are typically installed upstream of butterfly valves to intercept impurities and protect the valve and downstream equipment. The filter has a built-in drain port, allowing for direct cleaning without disassembly. The filter’s precision is typically 80-200 mesh; however, it’s important to note that higher mesh numbers result in finer filtration, but also greater pressure drop. Therefore, choose an appropriate mesh number and avoid blindly pursuing high precision.
Application Scenarios:
*Water Supply and Drainage Systems: Most commonly used in waterworks and sewage treatment plants.
*Industrial Circulating Water Systems: Pipelines in chemical and other applications requiring clean media.
*HVAC Systems: Used in conjunction with filters in cooling water circulation systems to prevent impurities from clogging heat exchangers.
*Fire Protection Systems: Butterfly valves, as the most common fire water control valve, are combined with filters to protect terminal equipment such as sprinkler heads.
Function Analysis:
Butterfly valves (especially soft-seal butterfly valves) are highly sensitive to impurities. Particulate matter entering can lead to:
*Valve seat scratches
*Seal failure
*Increased torque
*Shortened service life
2.2. Butterfly Valve + Pressure Reducing Valve
In high-pressure or high-pressure fluctuating systems, butterfly valves are often used in conjunction with pressure reducing valves. The butterfly valve is responsible for rapid shut-off, while the pressure reducing valve is used to stabilize downstream pressure. The typical configuration is: upstream butterfly valve + Y-type filter + pressure reducing valve + downstream butterfly valve.
Typical scenarios:
*High-rise building water supply: Municipal high-pressure water is first reduced to a suitable pressure by a pressure reducing valve, and then controlled by butterfly valves for zone control.
*Steam system: Boiler pressure is unstable, so pressure reduction and stabilization are required at the boiler outlet before distribution by butterfly valves.
*Agricultural irrigation: High-flow, low-pressure water supply.
Functional division:
Pressure reducing valve: Automatically adjusts and stabilizes pressure
Butterfly valve: Used for opening/closing or auxiliary regulation.
2.3. Butterfly valve + check valve
When water pumps or multi-branch systems are involved, a check valve is required. Installing a check valve at the pump outlet or on a ramped pipeline prevents backflow of the medium, avoids pump reversal and damage, and is also useful in water hammer systems.
Application Scenarios:
Pump Outlet
Parallel Piping
Elevation Difference Systems
2.4. Butterfly Valve + Control Valve
In automated control systems, butterfly valves are typically used in conjunction with control valves for precise flow control. The butterfly valve provides coarse regulation or isolation, while the dedicated control valve provides fine control of flow or pressure. This combination ensures control accuracy while facilitating equipment maintenance.
2.5. Butterfly Valve + Safety Valve
In high-pressure or high-temperature systems, a safety valve is also required for system protection.
Function: Automatically relieves pressure when system pressure abnormally increases, preventing equipment damage or accidents.
Butterfly valves cannot perform safety protection functions; therefore, this combination is essential in critical systems.
3. Typical System Diagrams and Installation Logic
To better understand the application of butterfly valves, the following are several typical system configurations:
3.1 Water Pump System
Water Source → Water Pump → Check Valve → Butterfly Valve → System
Features:
Check valve prevents backflow.
Butterfly valve is used for maintenance isolation.
3.2 Pressure-Reducing Water Supply System
Main Main Network → Butterfly Valve → Filter → Pressure-Reducing Valve → Butterfly Valve → User End
Features:
Embedded butterfly valves facilitate maintenance.
Filter protects pressure-reducing valve.
3.3 Industrial Control System
Media Source → Butterfly Valve → Control Valve → Butterfly Valve → Equipment
Features:
Control valve is responsible for precise control.
Butterfly valve achieves isolation.
4. Standard Installation Sequence Principles
In actual engineering, the installation sequence of valves is crucial and usually follows these principles. These principles not only affect system performance but also directly relate to equipment lifespan.
4.1 Basic Theory
Upstream → Filtration → Control → Protection → Downstream
4.2 Typical Installation Sequence
Y-type filter → Regulating/Pressure-reducing valve → Check valve → Butterfly valve
4.3 Key Rules
* Filter priority: Must be installed before precision valves
* Check valve near pump: Prevents backflow impact
* Butterfly valve for isolation: Usually placed before or after equipment
* Pressure-reducing valve on both sides: Facilitates maintenance
4.4 Other Considerations
* Valve spacing: At least 5 times the pipe diameter to avoid turbulence.
* Pressure drop: Pressure drop occurs at each valve, the amount is just a matter of degree. The total pressure drop is approximately equal to the sum of the pressure drops of each valve.
5. Butterfly Valve Selection Recommendations
Depending on the operating conditions, the selection of butterfly valves should vary depending on the medium and operating conditions:
5.1. Water Supply and Drainage System
Valve body: Ductile iron
Valve seat: EPDM Features: Low cost, good water resistance
Suggested combination: Filter + Check valve + Butterfly valve
5.2. Oils and Gases
Valve seat: NBR (oil resistant)
Valve plate: Stainless steel
Note: Avoid using EPDM valve seats
5.3. Chemical Media
Valve seat: PTFE
Valve plate: Fluorine-lined or stainless steel
Key: A high-efficiency filter must be configured.
5.4. High Temperature or Steam Systems
Type: Metal hard-seal butterfly valve
Suggested combination: Pressure reducing valve + Safety valve
6. Common Problems and Troubleshooting
*Filter clogging: Differential pressure alarm, regular draining.
*Butterfly valve leakage: Check sealing surface, butterfly plate deformation, or actuator limit.
*Unstable pressure: Check pressure reducing valve pilot valve and filter screen.
*Vibration and noise: Optimize opening, add a silencer, or change installation location.
*Improper installation: Flange misalignment and uneven bolt torque lead to leakage.
7. Summary
While butterfly valves are excellent, they are not a panacea. In practical engineering, only through proper combination with filtration, pressure stabilization, backflow prevention, and safety protection valves can an efficient, stable, and safe piping system be constructed.