Butterfly Gate

Butterfly gates serve as primary isolation and flow control devices in municipal water and wastewater treatment systems, utilizing a circular disc that rotates 90 degrees within the pipe bore to regulate flow. The gate operates through a quarter-turn actuator mechanism, with the disc positioned perpendicular to flow when closed and parallel when fully open. Typical installations achieve 99%+ shutoff capability with pressure drops under 5 psi at design flows. The primary trade-off is limited throttling control compared to globe valves, as butterfly gates are most effective in fully open or closed positions rather than intermediate flow modulation.

• Primary Clarifier Isolation: Butterfly gates serve as isolation valves on 12-48" influent and effluent lines, allowing operators to take individual clarifiers offline for maintenance without disrupting plant operations. Selected for tight shutoff and minimal headloss (0.1-0.3 feet) compared to gate valves.
• Secondary Process Control: Used on 8-36" RAS and WAS lines in activated sludge systems, providing flow isolation during pump maintenance or process adjustments. Operators prefer butterfly gates for their quick quarter-turn operation and visual position indication.
• Disinfection System Isolation: Common on 6-24" chlorine contact tank inlet/outlet piping, enabling individual basin isolation for cleaning or repair. The wafer design fits between flanged connections with minimal space requirements.
• Effluent Structure Control: Installed on 12-60" final effluent lines before discharge structures, providing emergency shutoff capability and routine isolation for outfall maintenance or sampling equipment servicing.

Daily Operations: Operators visually verify valve position using handwheel indicators or actuator position feedback. Manual valves require 90-degree rotation from full-open to full-closed. Electric actuators typically complete stroke in 30-120 seconds. Position verification critical before equipment maintenance or process changes.

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Maintenance: Quarterly lubrication of stem bearings and actuator components using marine-grade grease. Annual seat inspection requires valve cycling and leak testing at operating pressure. Maintenance requires confined space entry procedures when accessing below-grade installations. Basic mechanical skills sufficient for routine tasks; actuator repairs may require electrical technician support.

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Troubleshooting: Seat leakage appears as visible flow past closed disc, often caused by debris lodged in seat or worn elastomer coating. Excessive operating torque indicates stem binding or actuator malfunction. Typical service life 15-20 years for body components, 5-10 years for seats and actuators depending on duty cycle and water quality.

• Disc Assembly: Cast iron or ductile iron disc (6-60" diameter) with EPDM or Buna-N seat coating. Disc thickness typically 0.25-0.75" depending on size and pressure rating. Selection based on chemical compatibility and expected pressure differential.
• Body/Housing: Wafer-style cast iron or ductile iron body rated for 150-250 PSI working pressure. Lug-style bodies common for 6-24" applications; flanged bodies preferred for larger sizes requiring frequent removal.
• Stem and Bearing System: 316 stainless steel stem with bronze or stainless steel bushings. Upper and lower stem bearings handle operational torque. Stem diameter ranges from 0.75-2" based on valve size and torque requirements.
• Actuator Interface: Manual handwheel, electric motor operator, or pneumatic cylinder mounting capability. Torque requirements range from 50 ft-lbs (6" valve) to 2000+ ft-lbs (48" valve), determining actuator sizing.

• Flow Velocity Control: Maximum velocity: 8-10 fps for potable water, 6-8 fps for raw water applications; Minimum velocity: 2-3 fps to prevent settlement in 12-48" diameter lines; Pressure drop at full open: typically 0.5-2.0 psi for municipal applications
• Pressure Parameters: Working pressure: 150-250 PSI for distribution systems, up to 350 PSI for transmission mains; Pressure rating must exceed maximum system pressure by 25% minimum; Surge pressure consideration: add 50-100 PSI to static pressure for water hammer protection
• Physical Sizing: Valve diameter: 4"-48" typical for municipal plants (0.5-50 MGD capacity); Face-to-face dimensions per AWWA C504 standard; Actuator sizing based on breakaway torque: typically 1.5-2.0 safety factor
• Performance Requirements: Seat leakage: Class VI per ANSI/FCI 70-2 (maximum 0.1% of Cv); Operating temperature range: 32°F to 180°F for municipal water applications; Cycle life: minimum 10,000 full cycles for critical service applications

• Resilient vs. Metal Seat Selection: Resilient seats (EPDM/Buna-N) handle pressures up to 250 PSI with tight shutoff but degrade with chlorine >2 ppm or temperatures >180°F. Metal seats withstand higher pressures (350+ PSI) and chemical exposure but allow 2-5% leakage. Wrong choice leads to premature failure or inadequate shutoff capability.
• Actuator Type and Sizing: Manual operation suitable for <12" valves with <150 PSI. Electric actuators for remote operation require 120/480V power availability. Pneumatic actuators need 80-100 PSI instrument air. Undersized actuators cause incomplete closure; oversized units increase capital costs by 30-50%. Spring-return fail-safe adds 40% to actuator cost.
• End Connection Configuration: Wafer-style saves 60% in installation length but requires perfect flange alignment. Lug-style allows single-flange removal but costs 20% more. Flanged ends provide maximum flexibility but require 18-24" additional pipeline length. Wrong selection complicates maintenance access and increases installation costs.

• Primary: Division 40 22 13 - Gate Valves
• Secondary: Division 40 22 16 - Butterfly Valves
• Note: Butterfly gates combine characteristics of both valve types, with Division 40 22 16 being most applicable for disc-type closure mechanisms in water distribution systems.

• Material/Equipment Verification: Verify actuator torque ratings match valve requirements; Confirm seat material compatibility (EPDM vs Buna-N); Check flange drilling patterns and pressure ratings
• Installation Requirements: Minimum 5D upstream, 2D downstream clearance for accurate flow measurement; Access space for actuator maintenance (typically 24" minimum); Concrete thrust blocks for larger valves (>24")
• Field Challenges: Alignment issues with existing piping; Actuator mounting interference with adjacent equipment
• Coordination Issues: Electrical rough-in timing with actuator installation; Lead times: 12-16 weeks for larger valves with actuators

• DeZURIK - Eccentric plug valves (EPV Series) dominate municipal markets, 4"-120" sizes
• APCO - Model 700 butterfly valves with pneumatic actuators, strong in water treatment
• Bray - Series 30/31 resilient seated valves, popular for smaller plants
• AVK - Series 878 butterfly valves with proven municipal track record in distribution systems

• Gate valves - Better shutoff but slower operation, 20-30% higher cost. Preferred for isolation service.
• Ball valves - Excellent for throttling control, 40-60% higher cost than butterfly valves.
• Plug valves - Superior for slurry applications, similar cost to butterfly valves but higher maintenance. Butterfly valves offer best cost/performance balance for most municipal water applications.

Specify valve position indication early - many projects add limit switches as change orders. Build relationships with local manufacturer reps for faster technical support and competitive pricing on future projects. Consider standardizing on one manufacturer across facilities to reduce spare parts inventory. Request factory acceptance testing for critical applications; it's often included at no cost for larger valves.