Gate Valves

Gate valves provide full-bore isolation in municipal water and wastewater systems by lifting a wedge-shaped gate perpendicular to flow direction. The gate seats against two parallel sealing surfaces, creating a straight-through flow path when fully open and complete shutoff when closed. Typical pressure drop across fully-open gate valves ranges from 0.1-0.5 psi in municipal applications. While offering minimal head loss and excellent shutoff capability, gate valves are unsuitable for throttling service due to gate vibration and accelerated wear at partial openings.

• Raw Water Intake Isolation: Gate valves isolate intake pumps and transmission mains during maintenance. Selected for tight shutoff and minimal pressure drop when fully open. Typically 12"-48" flanged connections upstream of raw water pumps, downstream to transmission mains.
• Clearwell Isolation: Gate valves isolate finished water storage tanks from distribution systems. Critical for maintaining system pressure during tank maintenance. Usually 8"-24" flanged connections between clearwell outlets and high-service pumps.
• Process Line Isolation: Gate valves isolate treatment unit processes like filters, clarifiers, and chemical feed systems. Selected for infrequent operation and tight shutoff capability. Common sizes 4"-16" with flanged or mechanical joint connections upstream/downstream of process equipment.
• Transmission Main Sectioning: Gate valves provide emergency isolation on large transmission mains. Selected for full-bore design minimizing head loss. Typically 16"-48" with mechanical joint connections, spaced 1000-2000 feet along transmission routes.

Daily Operations: Gate valves require minimal daily monitoring since they operate in fully-open or fully-closed positions. Operators verify position indicators match system requirements and check for external leakage at packing glands. Valve position changes are infrequent, typically during planned maintenance or emergency response procedures.

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Maintenance: Annual exercising prevents seizure, requiring 2-person crews for large valves due to high operating torques. Packing gland adjustment every 2-3 years using standard wrenches. Confined space entry procedures required for vault-mounted valves. Internal inspection intervals of 10-15 years depending on water quality and valve cycling frequency.

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Troubleshooting: Common failures include seized stems from infrequent operation and gate binding from debris accumulation. Warning signs include increasing operating torque, external leakage at stem packing, and incomplete closure indicated by downstream flow. Typical service life ranges 25-40 years for buried installations, with stem packing replacement extending operational life significantly.

• Gate/Wedge: Solid or flexible wedge seals against valve seats. Bronze or stainless steel construction for 4"-12" valves, ductile iron with bronze facing for larger sizes. Flexible wedges accommodate thermal expansion in 8"+ applications.
• Stem: Non-rising stems standard for buried applications, rising stems for above-ground installations. Stainless steel 316 material, sized per AWWA C500/C509 standards. Typical thread pitches: 4-6 TPI for 4"-12", 3-4 TPI for 14"+ valves.
• Actuator: Manual gear operators standard for 8"+ valves, handwheels for smaller sizes. Electric actuators for remote operation require 480V/3-phase power. Sizing based on breakaway torque: typically 150-300% of operating torque.
• Body/Bonnet: Ductile iron per AWWA C509, epoxy-coated interior/exterior. Flanged ends for 4"-12", mechanical joint for 14"+. Working pressure ratings: 200-250 PSI standard, 300+ PSI available for high-pressure applications.

• Flow Velocity: 3-8 fps for water service, 2-5 fps for wastewater to minimize erosion and hydraulic shock. Maximum 10 fps in emergency conditions.
• Pressure Rating: Class 125-250 for distribution (50-200 psi), Class 150-300 for transmission mains (150-300 psi). High-pressure applications may require Class 600 (600 psi).
• Size Range: 4"-48" typical for municipal applications. Distribution: 6"-24" most common. Transmission: 16"-48" standard. Smaller than 4" generally use ball or butterfly valves.
• Head Loss: Fully open gate valves: 0.1-0.3 feet at design flow. Critical for pump system curves and energy calculations.
• Operating Torque: Hand-operated to 12" typically. Motor operators required above 16" or high-pressure service. Torque ranges: 8" = 200-400 ft-lbs, 24" = 2,000-5,000 ft-lbs.
• Seat Leakage: AWWA C515 allows 0.5% of Cv flow rate. Critical for isolation service.
• Burial Depth: Standard 4-6 feet. Deep burial (>8 feet) requires extended stems and special boxes.
• Temperature Range: -20°F to 180°F for potable water, up to 200°F for process applications.

• 1. Resilient vs. Metal Seated? Resilient wedge for pressures <200 psi and clean water service. Metal seated for high pressure (>200 psi), elevated temperature (>100°F), or abrasive service. Wrong choice: premature seat failure in 2-5 years vs. 20-year design life. Need: water quality analysis, operating pressure/temperature data.
• 2. Rising vs. Non-Rising Stem? Rising stem for above-ground installation and frequent operation (>50 cycles/year). Non-rising for buried service and infrequent operation. Wrong choice: stem damage from traffic loads or inability to determine valve position. Need: installation location, operating frequency, traffic loading.
• 3. Manual vs. Motor Operation? Manual operation acceptable to 12" diameter and <150 psi. Motor operators required for larger sizes, high pressure, or remote locations. Emergency power backup needed for critical isolation valves. Wrong choice: inability to operate during emergencies or excessive operator fatigue. Need: valve size, pressure, criticality assessment, power availability.
• 4. Ductile Iron vs. Cast Iron Body? Ductile iron for buried service, water hammer conditions, or seismic zones. Cast iron acceptable for above-ground, low-shock applications only. Wrong choice: catastrophic failure under stress. Need: installation conditions, seismic data, system hydraulics.

• Primary: 40 05 23 - Gate Valves
• Secondary: 33 11 00 - Water Utility Distribution Piping (for distribution system applications)
• Gate valves fall under Process Interconnections (Division 40) as control devices, with utility

• Material/Equipment Verification: Verify NSF-61 certification for potable water service, Confirm AWWA C515 compliance for resilient wedge valves, Check bolt torque specifications and gasket materials
• Installation Requirements: Minimum 6-inch clearance above valve for operation, Proper thrust blocking for buried installations, Valve box sizing coordination with utilities
• Field Challenges: Frozen valve boxes in northern climates, Interference with existing utilities during replacement, Access limitations in congested valve vaults
• Coordination Issues: Early coordination with paving contractors for valve box elevation, 12-16 week lead times for large diameter (>24") valves

• American Flow Control (AFC) - Series 2500 resilient wedge gate valves, dominant in western US municipal markets
• Clow Valve Company - F-6100 series iron body gates, strong Midwest presence with 150+ year municipal heritage
• Kennedy Valve - K-81 resilient seated gates, established southeastern municipal supplier
• Mueller Water Products - A-2360 series, broad national distribution through municipal dealer network

• Ball Valves - Better for frequent operation, 20-30% higher cost but superior sealing. Preferred for pump station isolation.
• Butterfly Valves - 40-50% lower cost for larger sizes (>12"), suitable for low-pressure applications but limited shutoff capability.
• Plug Valves - Excellent for slurry service, 50% higher cost, common in sludge handling applications. Gate valves remain standard for buried water main isolation due to proven reliability and lowest lifecycle cost.

Establish relationships with local valve service contractors early - they're invaluable for emergency repairs and know which manufacturers' parts are readily available. Specify valve position indicators on critical isolation valves to avoid costly "valve hunting" during emergencies. Consider stocking common repair parts (stems, wedges) for your predominant valve manufacturer. Group valve replacements by manufacturer to leverage bulk pricing - savings of 15-20% are typical on orders over $50K.