Butterfly Valves

Butterfly valves provide flow control and isolation in municipal water and wastewater systems through a rotating disc that pivots 90 degrees within the pipe bore. The disc, mounted on a central shaft, moves from fully closed (perpendicular to flow) to fully open (parallel to flow), offering quarter-turn operation with minimal pressure drop. Typical pressure drops range from 2-8 psi at full open position in 6-48 inch diameter applications. While butterfly valves excel in cost-effectiveness and compact installation footprint, they create turbulence downstream and cannot provide tight shutoff comparable to gate valves in critical isolation applications.

• Raw Water Intake Control: Butterfly valves regulate flow from intake structures to treatment facilities, typically 12-48 inches in diameter. Selected for low headloss (0.5-2 feet) and tight shutoff capability. Connected downstream to intake screens and upstream to raw water pumps.
• Clearwell Isolation: Used to isolate finished water storage compartments during maintenance, ranging 8-36 inches. Chosen for bubble-tight sealing and infrequent operation cycles. Positioned between clearwell sections and distribution pumps.
• Process Water Bypass: Control flow around treatment units like filters or clarifiers, typically 6-24 inches. Selected for throttling capability and quick operation during process upsets. Located on bypass piping around major treatment components.
• Effluent Discharge Control: Regulate treated effluent to receiving waters, commonly 12-60 inches. Chosen for reliable operation in outdoor environments and positive shutoff for regulatory compliance. Installed between final treatment and outfall structures.

Daily Operations: Operators monitor valve position indicators and verify proper seating through downstream pressure readings. Electric actuated valves require checking control signals and motor current draw. Manual valves need periodic position verification, especially on critical isolation applications where improper positioning affects process performance.

​

Maintenance: Quarterly lubrication of gear operators and annual packing adjustments maintain reliable operation. Seat replacement typically required every 5-10 years depending on cycling frequency. Confined space entry procedures apply for large buried valve maintenance. Maintenance staff need basic mechanical skills and standard hand tools.

​

Troubleshooting: Seat leakage appears as downstream flow when closed, indicating worn seals or debris interference. Excessive operating torque suggests bearing wear or stem binding. Actuator hunting indicates control system issues. Typical service life spans 15-25 years with proper maintenance, though seats and packing require more frequent replacement.

• Disc Assembly: Cast iron or stainless steel disc provides flow control, sized to match pipe diameter. Selection based on pressure rating (125-250 PSI typical) and corrosion resistance requirements for municipal water quality.
• Seat/Seal System: EPDM or Buna-N seats provide shutoff, with replaceable designs preferred. Material selection depends on chemical compatibility and temperature range (-20°F to 180°F typical municipal applications).
• Stem and Bearings: Stainless steel stems with bronze or polymer bearings handle operating torque. Sizing based on valve diameter and pressure differential, typically requiring 50-500 ft-lbs operating torque.
• Body Construction: Ductile iron or carbon steel bodies with epoxy coatings. Wafer, lug, or flanged end connections accommodate municipal piping systems from 3-72 inches.
• Actuator Interface: Manual gear operators or electric/pneumatic actuators. Selection based on operating frequency, remote control requirements, and available utilities at installation location.

• Flow Velocity Limits: Maximum: 8-10 ft/s for water service, 6 ft/s for wastewater to minimize erosion; Minimum: 2 ft/s to prevent settling in wastewater applications
• Pressure Parameters: Working pressure: 150-250 psi typical for municipal distribution; Pressure drop: 2-5 psi at full open position; Test pressure: 1.5x working pressure per AWWA C504
• Sizing Range: Diameter: 4" to 96" standard, with 6"-48" most common in municipal plants; Cv values: 24 (4") to 46,000 (48") for full-bore designs; Flow capacity: 100 GPM to 50,000 GPM typical range
• Performance Specifications: Seat leakage: Class IV (0.01% of Cv) minimum, Class VI preferred for critical isolation; Operating torque: 50-15,000 ft-lbs depending on size and pressure; Cycle life: 10,000-50,000 cycles for standard duty, 100,000+ for severe service; Temperature range: 32°F to 180°F for potable water, up to 200°F for process applications
• Actuator Requirements: Safety factor: 1.5-2.0x calculated torque for electric actuators; Fail position: Fail-safe closed for most isolation applications, fail-open for bypass services

• What disc configuration and seat material combination will provide required shutoff performance under system pressure? Eccentric designs with EPDM seats achieve Class VI shutoff to 150 psi, while concentric valves with nitrile seats typically limited to Class IV. Wrong choice results in excessive leakage, failed hydrostatic tests, and potential regulatory violations. Need: system pressure, shutoff class requirements, and media compatibility data.
• Should the valve be sized for line size or optimized for pressure drop and control characteristics? Full-bore sizing minimizes pressure drop (1-2 psi) but reduces control accuracy. Reduced-bore designs (one size smaller) improve control resolution by 15-25% but increase head loss to 3-5 psi. Incorrect sizing affects pump energy costs and control stability. Need: available head, control requirements, and energy cost analysis.
• What actuator torque and speed specifications are required for the application duty cycle? Standard duty actuators (10,000 cycles) cost 30-40% less than severe service units (100,000+ cycles). Under-specifying leads to premature failure and emergency replacement costs. Over-specifying wastes 20-30% of actuator budget. Need: expected cycle frequency, emergency closure time requirements, and maintenance budget constraints.
• Does the installation require fire-safe certification or special fugitive emission standards? Fire-safe valves meeting API 607 cost 15-25% more but mandatory for certain applications. Fugitive emission compliance per EPA Method 21 requires specific stem seal designs. Wrong specification creates regulatory compliance issues and retrofit costs. Need: local fire codes, EPA applicability, and environmental

• Verify NSF-61 certification for potable water contact
• Confirm AWWA C504 compliance for resilient seated types
• Check actuator torque ratings against valve requirements
• Minimum 5D upstream, 2D downstream clearance for accurate flow
• Proper pipe alignment critical - misalignment causes premature seat wear
• Actuator accessibility for maintenance

• Material/Equipment Verification: Verify NSF-61 certification for potable water contact; Confirm AWWA C504 compliance for resilient seated types; Check actuator torque ratings against valve requirements
• Installation Requirements: Minimum 5D upstream, 2D downstream clearance for accurate flow; Proper pipe alignment critical - misalignment causes premature seat wear; Actuator accessibility for maintenance
• Field Challenges: Disc interference with internal pipe debris during commissioning; Actuator mounting conflicts with adjacent piping/equipment
• Coordination Issues: SCADA integration requirements often overlooked until late; Lead times: 8-12 weeks standard, 16-20 weeks for large actuated valves

• Bray International - Series 31/41 resilient seated valves dominate municipal installations
• Keystone - Figure 990/991 high-performance series for critical shutoff applications
• Mueller Water Products - Centerline A-2360 series popular for distribution systems
• Emerson Fisher - 8560 series for process control applications
• All maintain strong municipal references with local rep support and standard AWWA compliance

• Gate valves preferred for infrequent operation (isolation duty) - 20% higher cost but better tight shutoff
• Ball valves chosen for slurry service or frequent cycling - 40% higher cost but superior durability
• Plug valves used for throttling applications requiring precise flow control - 60% higher cost
• Butterfly valves offer best cost/performance balance for frequent operation with moderate pressure drops in clean water service

Oversizing is common mistake - 6" valve in 8" pipe often performs better than 8" valve due to higher velocities keeping seats clean. Maintain manufacturer relationships - Bray and Keystone offer excellent field service for troubleshooting. Cost savings: Specify manual operators initially, add actuators later when budgets allow. Resilient seats: Replace every 15-20 years proactively rather than waiting for failure.